PLANCK2025 - The 27th International Conference From the Planck Scale to the Electroweak Scale

26 May 2025, 08:00 → 30 May 2025, 16:40 Europe/Rome

PLANCK2025 is the 27th  in the series of Conferences "From the Planck scale to the electroweak scale". The Conference is intended to bring together researchers working in high energy physics, covering a wide variety of formal, phenomenological and cosmological theoretical topics related to the present experimental programmes. 

Within the Conference, the talks of Thursday morning listed below are devoted to the MasieroFest, in celebration of Antonio' Masiero's many contributions and accomplishments.

 

Plenary speakers include: 

Riccardo Barbieri (MasieroFest) Laura Baudis Paolo Benincasa Chiara Caprini Michele Cicoli Gilberto Colangelo Joseph Conlon Laura Covi (MasieroFest) Valerie Domcke  Emilian Dudas Ferruccio Feruglio Nicolao Fornengo Shiu Gary Gian Francesco Giudice  (MasieroFest) Marco Gorghetto Christophe Grojean Arthur Hebecker Carlo Heissenberg Gino Isidori Seth Koren

Laurent Lellouch Yann Mambrini Silvia Manconi Guido Martinelli (MasieroFest) Matthew McCullough Angela Papa Silvia Pascoli Massimo Pietroni Maxim Pospelov Riccardo Rattazzi Nicole Righi Antonio Riotto Bemjamin Safdi Roberto Salerno Yael Shadmi Lorenzo Sorbo Yotam Soreq Andrea Wulzer Giulia Zanderighi

Important Notice: Conference Housing Information

We have been alerted by a participant who received an e-mail asking for personal informations for making a hotel arrangement. Please note that the conference organizers are not affiliated with any third-party agencies offering housing or accommodation services. We strongly advise participants to exercise caution and avoid sharing personal or financial information with third parties claiming to represent the conference.

 

Planck2025.pdf

Monday 26 May

08:00 Registration

08:45 Opening greetings

Plenary session: Monday morning

1 La Grande Bouffe: Flavor, Compositeness & Supersymmetry

Speaker: Riccardo Rattazzi (Lousanne)

2 Modular Invariance and the Strong CP Problem

Speaker: Ferruccio Feruglio (INFN Padova)

10:00 Coffee and registration

3 Flavor Physics: open problems & recent developments

Speaker: Gino Isidori (Zürich)

4 LHC Results: Review & Prospects

Speaker: Roberto Salerno (CNRS / Ecole Polytech.)

12:00 Buffet lunch

Plenary session: Monday afternoon

5 Fundamental physics with low energy muons

Speaker: Angela Papa (Pisa & PSI Villigen)

6 Physics highlights of the Future Circular Collider feasibility study

Speaker: Christophe Grojean (DESY)

7 The art of being precise

Speaker: Giulia Zanderighi (Munich)

8 Towards a Muon Collider

Speaker: Andrea Wulzer (Barcelona)

16:00 Coffee

9 Neutron stars as probes of dark sector

Speaker: Maxim Pospelov (Minnesota)

10 Stochastic gravitational wave background from axion inflation, and its phenomenology

Speaker: Lorenzo Sorbo (UMass Amherst)

11 Rich dark sectors: from the neutrino portal to gravitational waves

Speaker: Silvia Pascoli (Bologna)

12 Flavour Fusion

Speaker: Matthew McCullough (CERN)

Tuesday 27 May

Plenary session: Tuesday morning

13 Swampland, Stringy de Sitter, and the Measure Problem

Speaker: Arthur Hebecker (Heidelberg)

14 Black Holes and Quantum Gravity

Speaker: Gary Shiu (Wisconsin)

15 Recent Progress in String Inflation

Speaker: Michele Cicoli (Bologna)

16 String axions and associated relics

Speaker: Nicole Righi (King’s College)

11:00 Coffee

17 Beyond the Higgs with amplitude methods

Speaker: Yael Shadmi (Technion)

18 The timeless primordial universe and its combinatoric origin

Speaker: Paolo Benincasa (Munich)

12:30 Break for lunch

Collider Higgs Physics

Convener: Ramona Gröber (Università di padova)

19 Vector boson fusion & associated production of Higgs bosons as an LHC signature of CP violation

Many well-motivated extensions of the Standard Model predict new, entirely bosonic sources of CP violation (CPV). In these scenarios, the simultaneous observation of carefully selected bosonic processes emerges as a simple yet powerful method to unambiguously reveal the presence of CPV. The present study, which establishes a promising framework of CPV searches for the upcoming HL-LHC era, showcases this method by exploring the detectability of such generic CPV signatures within the economical Complex Two-Higgs Doublet Model (C2HDM). Specifically, we asses the observation prospects for viable combinations of gluon fusion, vector boson fusion and $V$-associated production processes which unequivocally signal the existence of CP-violating couplings within the bosonic spectrum of the model.

Speaker: Álvaro Lozano Onrubia (IFT UAM-CSIC & Universidad Autónoma de Madrid)

20 Refining Two-Loop Corrections to Trilinear Higgs Couplings

The precise determination of the Higgs self-couplings is an essential task for understanding electroweak symmetry breaking and probing physics beyond the Standard Model (SM). The calculation of two-loop corrections is important to provide a critical test of the perturbative stability, especially in the case of large one-loop corrections that can occur in scenarios with extended scalar sectors. Morever, they need to be taken into account for the future perspective of precisely measuring the Higgs self-couplings. In this talk, we will present our work on the leading two-loop corrections to the trilinear Higgs couplings in the two-Higgs-doublet model (THDM) and other models beyond the SM. We focus in particular on the couplings hhh, hhH , which are the most important for di-Higgs production at the (HL-)LHC. In our calculation we adress the renormalization of the alignment limit in the Higgs basis. We give some insights into the technical details of the calculation and discuss the phenomenological impact of our results.

Speaker: Alain Verduras Schaeidt (DESY)

21 How large can the light Yukawa couplings be?

The couplings of the Higgs boson to the massive gauge bosons, the third-generation quarks, the tau and the muon leptons have been measured and found to be in agreement with the predictions of the Standard Model. In contrast, the couplings to the first and second quark generations and to the electron are beyond experimental reach: the combination of their smallness and, for the quarks, the difficulty of tagging the particles in the detectors make the measurement of the Yukawa couplings of the light fermions experimentally challenging.

In our study we identify simplified UV models involving pairs of vector-like quarks which can generate significant enhancements of the quark Yukawa couplings. These models generate operators of the Standard Model Effective Field Theory at the tree-level and one-loop which are constrained by electroweak precision observables, Higgs data, and flavor physics. Accounting for such bounds, as well as the results of direct searches for vector-like quarks, considerable deviations in the Yukawa couplings of the light quark generations can still be obtained: first-generation quark Yukawa couplings are found to be enhanced up to several hundred times their Standard Model value, while the Higgs couplings to charm (strange) quarks can be increased by factors of a few (few tens). Electroweak Physics is found to play a significant role and we therefore also discuss projections for future measurements at the FCC-ee machine. In a similar spirit, we also consider how large deviation in the electron Yukawa coupling can become in concrete models in the light of the possibility of probing it in a dedicated run at the Higgs pole mass at the FCC-ee.

Speaker: Barbara Anna Erdelyi (Università degli Studi di Padova and INFN Sezione di Padova)

22 Walking in the Hidden Valley: Exploring dark parton showers in the "conformal window"

Dark-showers offer a compelling collider signature for Hidden Valley models featuring a confining dark sector. Our work extends these investigations to models with many more dark quark flavours where such theories enter the “conformal window''. Here, existing running coupling approximations in current event generators break down and so we must implement the exact two-loop RGE solution. This, alongside the two-loop Sudakov factor that employs this coupling, allows us to present the first phenomenological results of the parton showers of such near-conformal dark sectors.

Speaker: Joshua Lockyer (University of Graz)

23 Z-Portal Dark Pion Dark Matter and Dark Showers

A dark sector containing a confining non-abelian gauge group with multiple flavors of light dark quarks is expected to have dark pions being the lightest dark hadrons. The lightest dark pion, if stable, can be a dark matter candidate. The heavier dark pions can decay through the Z boson portal to the Standard Model (SM) particles if the light dark quarks mix with heavy electroweak doublets or from the dark Z’-Z mixing. The dark pion relic density is determined by the forbidden channel of light dark pions annihilating to heavier dark pions, or the heavy dark pion decay rate. The decay lengths of the heavy dark pions are typically macroscopic, and hence give distinctive collider signals. The usual direct or indirect searches of dark matter are not effective for this model. The dark showers generated by the Z decays into the dark sector and the FCNC decays of the SM mesons may provide the best probes.

Speaker: Hsin-Chia Cheng (University of California, Davis)

Dark Matter theory

Convener: Francesco D'Eramo (University of Padua)

24 Singlet-Doublet Fermionic Dark Matter in Gauge Theory of Baryons

We are considering a minimal $U(1)_B$ extension of the Standard Model (SM)
by promoting the baryon number as a local gauge symmetry to accommodate a
stable dark matter (DM) candidate. The gauge theory of baryons induces non-
trivial triangle gauge anomalies, and we provide a simple anomaly-free solution
by adding three exotic fermions. A scalar S spontaneously breaks the $U(1)_B$
symmetry, leaving behind a discrete $Z_2$ symmetry that ensures the stability of
the lightest exotic fermion originally introduced to cancel the triangle gauge
anomalies. Scenarios with weakly interacting DM candidates having non-zero
hypercharge usually face stringent constraints from experimental bounds on
the DM spin-independent direct-detection (SIDD) cross-section. In this work,
we consider a two-component singlet-doublet fermionic dark matter scenario,
which significantly relaxes the constraints from bounds on the DM SIDD cross-
section for suppressed single-doublet mixing. We show that the model offers
a viable parameter space for a cosmologically consistent DM candidate that
can be probed through direct and indire

Speaker: TARAMATI Taramati (Indian Institute of Technology, Bhilai, 491002)

25 Unveiling Imprints from Dark Symmetries: Signatures of Axion Portal to Scalar Dark Matter

If dark matter is blind to standard model gauge interactions, the dark sector might not be totally secluded but connect to the visible sector via the introduction of portal interactions. In this talk, I will discuss a novel scenario where an axion-like particle acts as mediator between the SM and a complex scalar singlet dark matter candidate. The identification of physical couplings crucially incorporates a profound connection to the underlying symmetry that stabilizes the dark matter particle. In particular, I will examine the case of non-Abelian discrete symmetries and show how these prevent dark matter portal interactions to be removed via field redefinitions. This choice leaves peculiar imprints on both cosmological evolution and late times phenomenology. I will discuss how dark matter relic abundance is solely determined by freeze-out of semi-annihilations and is independent of portal couplings to the visible sector. While naturally evading direct detection constraints, rich and peculiar indirect detection spectra are uniquely determined by the one-step cascade DM semi-annihilation rate, with visible decay channels of the mediator only affecting the spectral shape.

Based on arXiv:2502.19491 .

Speaker: Tommaso Sassi (Università di Padova, INFN Padova)

26 Freeze-In at Strong Coupling in a $Z^\prime$-Mediated Dark Matter Scenario

We present a freeze-in production mechanism for fermionic dark matter mediated by a $Z^\prime$ gauge boson. Freeze-in is typically a production mechanism for FIMPs. However, if the temperature of the Standard Model (SM) thermal bath never exceeds the dark matter mass, we enter a regime of Boltzmann-suppressed production. This allows for stronger couplings in a freeze-in scenario, reaching gauge couplings of up to order one. In this context, current and future direct detection dark matter experiments play a crucial role in constraining the model.

Speaker: David Cabo Almeida (University of Messina (Italy) & University of Barcelona (Spain))

27 Cogenesis of baryon and dark matter from ultra-light PBH

We discuss the possibility of producing the observed baryon asymmetry of the Universe (BAU) and dark matter (DM) from evaporating primordial black holes (PBH) incorporating semi-classical regime and memory burden regime. In the simplest scenario of baryogenesis via vanilla leptogenesis with hierarchical right handed neutrino (RHN), it is possible to generate the observed BAU with PBH being sole contributor to the production of RHN. While it is not possible to achieve cogenesis in this minimal setup due to structure formation constraints on relic allowed DM parameter space, we show the viability of successful cogenesis in the resonant leptogenesis regime. We also show that successful cogenesis can be achieved in a simple baryogenesis model without taking the leptogenesis route. Due to the possibility of generating asymmetry even below the sphaleron decoupling era, the direct baryogenesis route opens up new parameter space of memory-burdened PBH. The two scenarios of successful cogenesis can also be distinguished by observations of stochastic gravitational waves produced from PBH density fluctuations.

Speaker: Nayan Das (Indian Institute of Technology Guwahati)

28 Probing GUT with Accidentally Stable Dark Matter

In this talk, I will consider extensions of the Standard Model (SM) featuring vectorlike fermions charged under a new confining force, referred to as 'dark color.' These dark fermions condense to form a spectrum of dark hadrons, with the lightest accidentally stable dark baryon, with a mass of around 100 TeV, serving as a viable thermal dark matter candidate. I will, in particular, consider the grand unified theory (GUT) SU(5) framework for these models, highlighting how gauge coupling unification within the SM imposes stringent constraints on their construction. Additionally, I will discuss the unique cosmological scenarios these unified theories present and their phenomenological implications.

Speaker: Sonali Verma (ULB, Brussels)

First order phase transitions

Convener: Luca Martucci (University of Padua)

29 Quantisation across Bubble Wall and Friction

I will start by explaining why it is interesting and how one can quantise from first principles field theories living on the background of a bubble wall in the planar limit, i.e. a domain wall, with a particular focus on the case of spontaneous breaking (and restoring) of gauge symmetry. Using the tools I introduced, we can compute the average momentum transfer from transition radiation, which denotes the soft emission of radiation by a high-energetic particle passing across the wall, with a particular focus on the longitudinal polarisation of vector bosons. We find this latter one to be comparable to transverse polarisations in symmetry-breaking transitions with mild super-cooling, and dominant in broken to broken transitions with thin walls. Our results have phenomenological applications for the expansion of bubbles during first-order phase transitions. Our general framework allows for the calculation of any particle processes of interest in such translation breaking backgrounds.

Speaker: Giulio Barni (IFT Madrid)

30 Bubble Nucleation and Gravitational Waves from Strongly Coupled QFT's

Gravitational waves emitted from FOPTs of strongly coupled QFTs are, at present, a daunting task to accurately predict due to their strong coupling nature. This talk demonstrates how to predict the gravitational wave spectra of Strongly coupled QFTs using holography and lattice data input for a pure SU(N) Yang-Mills theory. We will display how holography may be useful in constructing an effective action. Once the effective action is in our grasp, we will use this to study bubble nucleation to estimate the gravitational wave spectra and comment on other phenomenological consequences.

Speaker: Nicklas Ramberg (SISSA Trieste)

31 Bubble wall velocity from hydrodynamics

Terminal velocity reached by bubble walls in cosmological first-order phase transitions is an important parameter determining both primordial gravitational wave spectrum and the production of baryon asymmetry in models of electroweak baryogenesis. In this talk I discuss the recent results for local thermal equilibrium approximation for which, using hydrodynamic simulations, we have confirmed that pure hydrodynamic backreaction can lead to steady-state expansion. However, this is not the generic outcome. Instead, it is much more common to observe runaways, as the early-stage dynamics right after the nucleation allow the bubble walls to achieve supersonic velocities before the heated fluid shell in front of the bubble is formed. In order to capture this effect, we generalized the analytical methods beyond the local thermal equilibrium and find a qualitative way to predict whether the runaway is physical, which has a crucial impact on cosmological observables.

Speaker: Mateusz Zych (University of Warsaw)

32 Inverse bubbles from broken supersymmetry

The dynamics of first order phase transitions shows a non-trivial interplay between the bubble wall and the surrounding plasma, which is fundamental in determining the phenomenology of the phase transition including the associated gravitational wave emission. Building upon recent findings on inverse phase transitions in the early Universe, in this talk I will present the first natural realization of this phenomenon within a minimal O’Raifeartaigh model for supersymmetry breaking. As we shall see, inverse hydrodynamics, which is characterized by the fluid being sucked in by the expanding bubble rather than being pushed / dragged as in standard deflagration / detonation modes, is actually not limited to a phase of (re)heating but can also occur for phase transitions while the Universe cools down, related in this case to spontaneous R-symmetry breaking. This provides a proof of principle highlighting the need to account for these new fluid solutions when considering cosmological phase transitions and their phenomenological implications. The talk is mostly based on [2406.01596] and [2503.01951].

Speaker: Simone Blasi (DESY Hamburg)

33 TBD

Neutrinos

Convener: Stefano Rigolin

34 Disorder and Neutrino Flavour

It has been recently shown by Craig and Sutherland that disorder in linear mass chains can lead to localisation of wave functions a la anderson localisation in 4D. Such localisation can be used to understand tiny neutrino masses. In the present work, we generalise this localisation mechanism over several geometries for the mass chains and study neutrino masses and flavor mixing. We show that in the limit of strong disorder, these models predict hierarchical neutrino masses and anarchical mixing angles. This is true for all geometries of the mass chains and whether the couplings are “local”, “non-local” or “mixed.” On the other hand, if one considers weak disorder scenarios, it is possible to explain flavour mixing angles within the experimental range, within a few parameters similar to a flavour models a la Froggatt-Nielsen. We present several models where this is possible and also the associated flavour and collider phenomenology.

Speaker: Mr Sudhir Vempati (Centre for High Energy Physics, Indian Institute of Science, Bangalore 560012)

35 Testing the dark origin of neutrino masses with oscillation experiments

The origin of neutrino masses remains unknown to date. One popular idea involves interactions between neutrinos and ultralight dark matter, described as fields or particles with masses $m_\phi \lesssim 10\,\mathrm{eV}$. Due to the large phase-space number density, this type of dark matter exists in coherent states and can be effectively described by an oscillating classical field. As a result, neutrino mass-squared differences undergo field-induced interference in spacetime, potentially generating detectable effects in oscillation experiments. By analyzing data from the Kamioka Liquid Scintillator Antineutrino Detector (KamLAND), a benchmark long-baseline reactor experiment, we show that the hypothesis of a dark origin for the neutrino masses is disfavored for $m_\phi \lesssim 10^{-14}\,\mathrm{eV}$, compared to the case of constant mass values in vacuum. The mass range $10^{-17}\,\mathrm{eV} \lesssim m_\phi \lesssim 10^{-14}\,\mathrm{eV}$ can be further tested in current and future oscillation experiments by searching for time variations (rather than periodicity) in oscillation parameters. Furthermore, we demonstrate that if $m_\phi\gg 10^{-14}\,\mathrm{eV}$, the mechanism becomes sensitive to dark matter density fluctuations, which suppresses the oscillatory behavior of flavor-changing probabilities as a function of neutrino propagation distance in a model-independent way, thereby ruling out this regime.

Speaker: Hong-Yi Zhang (Tsung-Dao Lee Institute)

36 Neutrino Phenomenology from Flavor Deconstruction

Flavor deconstruction refers to a framework where the three fermion families are charged under non-universal gauge groups. Such Standard Model extensions have been proven to be capable of explaining flavor hierarchies among charged fermions. Recently, it has been shown that also neutrino anarchy can be realized within flavor-deconstructed models exploiting a seesaw mechanism. The present work aims to investigate the phenomenological implications of flavor deconstruction in the leptonic sector. In particular, we show that lepton-flavor-violating processes such as µ → eγ, µ → eee and µ-e conversion in nuclei are among the best probes of our scenario. Despite the large number of UV parameters in a general setup, we identify a limited set of combinations relevant to phenomenology. Specifically, we classify flavor-deconstructed models with neutrino anarchy and determine the minimum new-physics scale, Λ, required for their viability. Notably, for certain models, Λ can be as low as a few TeV.

Speaker: Andrea Sainaghi (University of Padua and INFN Padua)

37 Neutrino Masses and Nucleon Decay as Probes of Standard Model Linear Extensions

Baryon and lepton number are excellent low-energy symmetries of the Standard Model (SM) that tightly constrain the form of its extensions. In this paper we investigate the possibility that these accidental symmetries are violated in the deep UV, in such a way that one multiplet necessary for their violation lives at an intermediate energy M above the electroweak scale. We write down the simplest effective operators containing each multiplet that may couple linearly to the SM at the renormalisable level and estimate the dominant contribution of the underlying UV model to the pertinent operators in the SMEFT: the dimension-5 Weinberg operator and the baryon-number-violating operators up to dimension 7. Our results are bounds on the scale M for each multiplet–operator pair,derived from neutrino-oscillation data as well as current and prospective nucleon-decay searches. In addition, we advocate that our framework provides a convenient and digestible way oforganising the space of UV models that violate these symmetries.

Speaker: Arnau Bas i Beneito (Institut de Física Corpuscular (IFIC) - Universitat de València (UV))

38 A new modular mechanism for neutrino masses from low-scale seesaw

In the presence of a finite modular flavour symmetry, fermion mass hierarchies may be generated by a slight deviation of the modulus from a symmetric point. This small parameter governing charged-lepton mass hierarchies may also be responsible for the breaking of lepton number in a symmetry-protected low-scale seesaw. In this talk, I will illustrate the implementation and the phenomenological implications of this connection.

Speaker: Matteo Parriciatu (Università Roma Tre e INFN Sezione Roma Tre)

16:00 Coffee Break

Axions

Convener: Stefano Rigolin

39 Time modulation of nuclear decays deep-underground as a probe of axion dark matter

We investigate the time modulation of alpha and weak nuclear decays as a method to probe axion dark matter. To this end, we develop a theoretical framework to compute the $\theta$-dependence of alpha and weak nuclear decays, including electron capture and $\beta$ decay, which enables us to predict the time variation of alpha and weak radioactivity in response to an oscillating axion dark matter background. As an application, we recast old data sets, from the weak nuclear decays of ${^{40}\text{K}}$ and $\ce{^{137}Cs}$ taken at the underground Gran Sasso Laboratory, in order to set constraints on the axion decay constant, specifically in the axion mass range from few $10^{-23}\;$eV up to $10^{-19}\;$eV. We finally propose a set of new measurements at the Gran Sasso Laboratory, based on the weak nuclear decay of ${^{40}\text{K}}$ via electron capture and on the alpha decay of ${^{241}\text{Am}}$, in order to explore even shorter timescales, thus reaching sensitivities to axion masses up to $10^{-9}\;$eV.

Speaker: Claudio Toni (LAPTh, CNRS)

40 Tackling ALP searches in meson decays with ALPaca: a phenomenological approach

Part of the community has intensively searched for ALP signals, as well as conducted dedicated data analyses to identify potential evidence of New Physics compatible with an ALP, resulting in constraints on the ALP parameter space. Therefore, it is now the time to present a tool, ALPaca, that facilitates the combination among the different information on ALP physics.
The focus of this talk will be on a phenomenological analysis of the ALP theory using the most up-to-date data from flavour facilities, to show both the latest constraints and the potential of ALPaca.

Speaker: Marta Fuentes Zamoro (Universidad Autónoma de Madrid)

41 Axion-like particles and CP violation

CP-violating probes are among the most promising and yet relatively unexplored ways to look for Axion-Like Particles (ALPs) and to investigate their phenomenology. In this talk, I will offer a complete and up-to-date overview of these new physics candidates. First, I will discuss in detail the phenomenology associated to this class of ALPs, with a focus on the possibility to probe them by studying their indirect impact on the electric dipole moments (EDMs) of particles, nucleons, nuclei and molecules. In the second part of the talk, I will rather muse on the possible origin of these particles. In doing so, I will provide an overview of the possible UV completions leading to the appearance of a CP-violating ALP and I will discuss the different predictions that can be drawn from each specific scenario.

Speaker: Gabriele Levati (ITP, University of Bern)

42 Non-Invertible Peccei-Quinn Symmetry, Natural 2HDM Alignment, and the Visible Axion

We identify $m^2_{12}$ as a spurion of non-invertible Peccei-Quinn symmetry in the type II 2HDM with gauged quark flavor. Thus a UV theory which introduces quark color-flavor monopoles can naturally realize alignment without decoupling and can furthermore revive the Weinberg-Wilczek axion. As an example we consider the SU(9) theory of color-flavor unification, which needs no new fermions. This is the first model-building use of non-invertible symmetry to find a Dirac natural explanation for a small relevant parameter.

Speaker: Antonio Delgado (University of Notre Dame)

43 Froggatt-Nielsen ALP

Froggatt-Nielsen models typically predict the existence of a light axion-like particle, pushing the new dynamic to a very high scale.
In this talk I will focus on models based on $Z_N$ discrete symmetries, which are counterexamples in which the new scale might in fact be much lower.
I will first chart the allowed parameter space from a set of theoretical considerations, and then focus on a minimal model based on $Z_4$ symmetry. For this, I will introduce an explicit renormalizable UV completion and study the model's phenomenology in detail, highlighting the interplay between the effects of the ALP and of the UV fields.

Speaker: Alessandro Valenti (University of Basel)

44 Small Instanton-induced Flavor Invariants and the Axion Potential

Small instantons which increase the axion mass due to an appropriate modification of QCD at a high energy scale, can also enhance the effect of CP-violating operators to shift the axion potential minimum by an amount $\theta_{\rm ind}$, which is severely constrained by neutron electric dipole moment (nEDM) experiments.
In this talk, focusing on the dimension-six CP-odd operators in the Standard Model Effective Field Theory (SMEFT), we will introduce a new set of determinant-like flavor invariants that naturally arise in the instanton computation of the quantity $\theta_{\rm ind}$. We will show that these flavor invariants are useful for anticipating how CP-violating SMEFT operators participate in the instanton computations and for classifying the leading effects from the Wilson coefficients. More generally, the flavor invariants, together with an instanton Naive Dimensional Analysis, can be used to more accurately estimate small instanton effects in the axion potential that arise from any SMEFT operator and to conveniently probe the impact of different flavor assumptions on the bounds obtained from $\theta_{\rm ind}$.
Reference: arXiv: 2402.09361 (https://arxiv.org/pdf/2402.09361)

Speaker: Pham Ngoc Hoa Vuong (Deutsches Elektronen-Synchrotron DESY)

Dark Matter experiments

Convener: Francesco D'Eramo (University of Padua)

45 Linear response theory for light dark matter-electron scattering in materials

I combine the non-relativistic effective theory of dark matter (DM) - electron interactions with linear response theory to obtain a formalism that fully accounts for screening and collective excitations in DM-induced electronic transition rate calculations for general DM-electron interactions. In the same way that the response of a dielectric material to an external electric field in electrodynamics is described by the dielectric function, so in our formalism the response of a detector material to a DM perturbation is described by a set of generalised susceptibilities which can be directly related to densities and currents arising from the non-relativistic expansion of the Dirac Hamiltonian. I apply our formalism to assess the sensitivity of non-spin-polarised detectors, and find that in-medium effects significantly affect the experimental sensitivity if DM couples to the detector's electron density, while being decoupled from other densities and currents. Our formalism can be straightforwardly extended to the case of spin-polarised materials.

Speaker: Riccardo Catena (Chalmers University of Technology)

46 Constraining ALP-nucleon interactions with neutrino water Cherenkov detectors via the diffuse flux of MeV ALPs from galactic supernovae

Axion-like particles (ALPs) can be copiously produced in core-collapse supernovae (SNe) due to their coupling to SN matter. If they are weakly coupled, ALPs leave the star unimpeded after being produced. This regime has already been tightly constrained by cooling bounds. In this talk, I will focus on the trapping regime, where the SN environment becomes optically thick for ALPs and, therefore, they cannot free-stream out of the star and become trapped. Even in this regime, a vast flux of ALPs can escape and arrive to Earth. In particular, I will consider MeV ALPs that are produced in the SN interior through their coupling to nucleons and escape with semi-relativistic velocities. I will argue that they can constitute a diffuse flux formed by the overlap of ALP fluxes from different SN, which can be probed by current neutrino water Cherenkov detectors via $a \, p → p \, \gamma$ . Using existing Super-Kamiokande data, we can place new constraints on ALP interactions with nucleons, extending existing bounds beyond cooling limits. In particular, we exclude a region spanning more than one order of magnitude in the ALP-proton coupling above cooling bounds for ALP masses in the range of $1-80$~MeV and ALP-proton couplings between $8\times10^{-6}-2\times10^{-4}$.

Speaker: Marina Cermeño Gavilan (IFT UAM-CSIC)

47 A general upper bound on the light dark matter scattering rate in materials

Within the framework of linear response theory combined with effective description of interactions of fermion dark matter (DM) with electrons, it is possible to derive a material-independent theoretical upper limit on the rate of DM-induced electronic excitations in direct-detection experiments. In my talk, I will describe how this limit can be obtained, and compare it to the interaction rate calculated for some actual materials, in a few popular effective models of DM-$e^-$ interactions.

Speaker: Michał Iglicki (Chalmers U. of Technology)

48 First results from the LEGEND Experiment

Neutrinoless double beta decay (0νββ) is a hypothetical process that, if observed, would establish that neutrinos are Majorana particles. The LEGEND (Large Enriched Germanium Experiment for Neutrinoless ββ decay) Experiment is designed to search for the 0νββ decay ⁷⁶Ge → ⁷⁶Se + 2e-, with high-purity germanium (HPGe) detectors enriched in ⁷⁶Ge. The experimental signature of 0νββ is a monoenergetic peak at the decay Q-value (Q_ββ), which for ⁷⁶Ge is 2039 keV.

The LEGEND Experiment builds on the success of the GERDA and MAJORANA DEMONSTRATOR experiments to search for 0νββ in ⁷⁶Ge. The HPGe detectors serve both as the source of the decaying isotope and as sensors for the emitted electrons and are operated in liquid argon (LAr) to suppress backgrounds. The first phase of the experiment, LEGEND-200, is currently collecting physics data at the Gran Sasso National Laboratories, aiming to probe the effective Majorana mass down to ~35 meV.

LEGEND employs advanced background suppression techniques, including pulse shape discrimination in the semiconducting diodes and active vetoes using both a muon veto and a liquid argon veto. The next phase, LEGEND-1000, will further advance the sensitivity frontier aiming for half-lives beyond 10²⁸ years and probing Majorana masses down to ~10 meV.

In this presentation, we will provide an overview of LEGEND, detailing its experimental strategy, background mitigation techniques, and the latest results from LEGEND-200, as well as prospects for LEGEND-1000.

This work is supported by the U.S. DOE and the NSF, the LANL, ORNL and LBNL LDRD programs; the European ERC and Horizon programs; the German DFG, BMBF, and MPG; the Italian INFN; the Polish NCN and MNiSW; the Czech MEYS; the Slovak RDA; the Swiss SNF; the UK STFC; the Canadian NSERC and CFI; the LNGS and SURF facilities.

Speaker: Francesco Borra (Roma Tre University, INFN)

49 Did IceCube discover Dark Matter around Blazars?

Blazars are a subclass of active galactic nuclei (AGN), the brightest continuously emitting sources in the Universe, powered by accreting supermassive black holes (SMBH). Their defining characteristic is the presence of powerful, back-to-back relativistic jets of protons and electrons, with one jet closely aligned in the direction of Earth. This offers a unique opportunity to probe physics Beyond the Standard Model. The jet can in fact interact with the surrounding Dark Matter in the host galaxy’s halo, where the presence of the SMBH induces a spike in density, offering compelling direct and indirect detection prospects. A key signature of this interaction is the production of high-energy neutrinos, as secondary products of the proton disintegrating in the collision. The resulting outgoing neutrino flux is qualitatively and quantitatively different from the one expected via Standard Model processes alone and, notably, provides a better fit to observations for a large region of unexplored light Dark Matter parameter space. This raises the intriguing question of whether high-energy neutrino observations from blazars could represent the first indirect detection of Dark Matter.

Speaker: Andrea Giovanni De Marchi (Università di Bologna and INFN)

50 TBD

Formal

Convener: Luca Martucci (University of Padua)

51 Dark heterotic axions

Among various predictions of string compactifications, axions hold a pivotal role, as they provide a unique avenue to tie UV physics to experiments. 
Most experimental setups aim to detect a signal using the direct coupling between the axion and the Standard Model.
If string axions coupled to Abelian gauge fields undergo slow-roll during inflation, they produce a multi-peak GW signal whose magnitude depends on the details of the compactification. We build on previous workman in Type IIB string theory, where the Chern-Simons coupling is highly constrained, limiting the viability of this mechanism. Motivated by this, we turn to heterotic string theory, where we explore the role of axions and their Chern-Simons coupling to a hidden Abelian gauge field, investigating its potential observational consequences.

Speaker: Margherita Putti (DESY / University of Hamburg)

52 Gauge-invariant Amplitudes Decomposition for Massive Gauge Theories

We provide a gauge-invariant decomposition of Feynman amplitudes in spontaneously broken gauge theories. Amplitudes are graded according to the number $l_h$ of internal lines of the propagating gauge-invariant field that represents the physical Higgs scalar and the number $l_v$ of internal lines of the propagating gauge-invariant field describing the massive vector meson.
Slavnov-Taylor identities hold separately for each $(l_h,l_v)$-sector.
The amplitudes subspace $l_h>0,l_v>0$ contains inside loops only physical propagating degrees of freedom.
We discuss the application of the formalism to the restoration of Slavnov-Taylor identities broken by intermediate regularization in the example of a chiral massive Abelian gauge model.

Speaker: Andrea Quadri (INFN - Sez. di Milano)

53 No gauge cancellation at high energy in the five-vector $R_\xi$ gauge

We propose a novel $R_\xi$ gauge in the five-vector (5V) framework within the Abelian Higgs model. In the Cartesian basis of the complex Higgs field, the 5V $R_\xi$ gauge ensures non-divergent tree-level amplitudes for each Feynman diagram in the high-energy limit. This framework pinpoints the origin of high-energy divergences in tree-level amplitudes for each diagram, providing a criterion for quantifying the degree of divergences from other gauges. The 5V description necessitates treating the Goldstone field as the fifth gauge-field component, offering deeper insight into the dynamics of massive gauge bosons, particularly its longitudinal mode. The impact of this framework is demonstrated by rigorously comparing tree-level amplitudes from the 5V $R_\xi$ gauge with those from the conventional 4V $R_\xi$ gauge and the Feynman diagram gauge, the latter of which exhibits no gauge cancellation, similar to the 5V $R_\xi$ gauge.

Speaker: Jaehoon Jeong (KIAS (Korea Institute for Advanced Science))

54 Superadditivity at Large Charge

The weak gravity conjecture has been invoked to conjecture that the dimensions of charged operators in a CFT should obey a superadditivity relation (sometimes referred to as convexity). In this work, we study superadditivity of the operator spectrum in theories expanded about the semi-classical saddle point that dominates correlators of large charge operators. In particular, we construct bottom-up effective field theories with the goal of violating the conjecture. We indeed find such an EFT, though are forced in the process to introduce a dilaton field. This demonstrates that while the superadditivity conjecture cannot be proven using bottom-up arguments alone, a conjecture-violating theory would require the very tall order of an infinitely tuned potential.

Speaker: Andrew Gomes (EPFL)

55 Functional Methods Beyond One-Loop Order

We present recent advances in functional techniques beyond one-loop order suitable for precision matching and running computations in the effective field theories. Expanding the generating functional and quantum effective action up to two-loop order, we analyze how the relevant terms can be evaluated. The formalism is then generalized to theories with mixed spin as well as gauge fields, where we show how the gauge covariance can be preserved in the evaluation of the quantum effective action. Finally, we demonstrate the application of this formalism through two concrete examples: scalar toy model and Euler-Heisenberg Lagrangian in QED.

Speaker: Ajdin Palavric (University of Basel)

56 Lack of propagating degrees of freedom in degenerate f(R) models

In the context of $f(R)$ gravity, as well as other extended theories of gravity, the correct counting of globally well-defined linear dynamical modes (i.e. gravitational-wave polarisations) has recently drawn a vivid interest. In this talk, we present a consistent approach shedding light on such issues for both so-called degenerate and non-degenerate $f(R)$ models embedded in Minkowski and de Sitter backgrounds. We find that the linearised spectrum of degenerate models on these backgrounds is empty, lacking both the graviton and scalaron modes which appear in generic non-degenerate models. Our work generalises previous results in the literature applicable only to the specific (degenerate) model $f(R)=\alpha R^2$; in fact, we find that the same pathologies discovered therein emerge for all choices of $f(R)$ belonging to the wide class of degenerate models.

Speaker: Adrián Casado-Turrión (Center for Physical Sciences and Technology (FTMC, Lithuania))

Inflation

Convener: Paride Paradisi (Padova U. and INFN)

57 The Schwinger effect during axion inflation

The production of gauge fields during inflation, in particular, in the axion inflation model, has a lot of phenomenological applications as it may impact the background inflationary dynamics, alter the spectral properties of primordial scalar and tensor perturbations, and give rise to charged particles via the Schwinger effect. The latter can strongly reduce the efficiency of gauge-field production during axion inflation. It is therefore crucial to have a clear understanding and proper description of this phenomenon to obtain reliable predictions for the physical observables in this model. In the present work, we revisit the problem of Schwinger pair-production during axion inflation in the presence of both electric and magnetic fields and improve on the state of the art in two ways: (i) taking into account that the electric- and magnetic-field three-vectors are in general noncollinear, we derive the vector decomposition of the Schwinger-induced current in terms of these fields and determine the corresponding effective electric and magnetic conductivities; (ii) by identifying the physical momentum scale associated with the pair-creation process, we incorporate Schwinger damping of the gauge field in a scale-dependent fashion in the relevant equations of motion. Implementing this new description in the framework of the gradient-expansion formalism, we obtain numerical results in a benchmark scenario of axion inflation and perform a comprehensive comparison with earlier results in the literature. In some cases, the resulting energy densities of the produced gauge fields differ from the old results by more than one order of magnitude, which reflects the importance of taking the new effects into account.

Speaker: Oleksandr Sobol (University of Münster)

58 Gravitational waves production by inflationary transitions in U(1) aligned natural inflation

The original axion natural inflation model predicts a tensor-to-scalar ratio exceeding experimental limits. In contrast, aligned axion inflation allows for inflationary trajectories that begin near a saddle point of the two-field potential and terminate due to an instability in the orthogonal direction. These solutions are consistent with current observational constraints, and upcoming CMB experiments will probe a range of parameter values.
Previous studies have suggested the possibility of two distinct inflationary stages separated by a transition characterized by rapid oscillations of the fields. In this work, we demonstrate that the existence of these two stages is a generic feature of the model. We explore a possible phenomenological signature of the transition when the model is coupled to a U(1) gauge field, namely, the production of gravitational waves (GWs) sourced by gauge quanta generated during the transition. We find that the resulting GW power spectrum exhibits a sharp peak at the transition scale, potentially detectable by future GW experiments. This mechanism produces a feature similar to that seen in spectator axion models but emerges naturally within the framework of saddle-point inflation in the aligned axion model.

Speaker: Federico Greco (University of Padova)

59 Modular invariant Inflation, reheating and leptogenesis

We propose new classes of inflation models based on the modular symmetry, where the modulus field τ serves as the inflaton. We establish a connection between modular inflation and modular stabilization, wherein the modulus field rolls towards a fixed point along the boundary of the fundamental domain. We find the modular symmetry strongly constrain the possible shape of the potential and identify some parameter space where the inflation predictions agree with cosmic microwave background observations. The tensor-to-scalar ratio is predicted to be smaller than $10^{-6}$ in our models, while the running of spectral index is of the the order of $10^{-4}$. We will also give a concrete model where modulus field can be used to realize the inflaiton as well as the correct lepton masses and mixing structures through a Seesaw mechanism. This naturally give channels for reheating and leptogenesis.

Speaker: Wenbin Zhao (University of Bonn)

60 Schwinger Current in de Sitter Space

We study classical background electric fields and the Schwinger effect in de Sitter space. We show that having a constant electric field in de Sitter requires the photon to have a tachyonic mass proportional to the Hubble scale. This has physical implications for the induced Schwinger current which affect its IR behaviour. To study this we recompute the Schwinger current in de Sitter space for charged fermions and minimally coupled scalars imposing a physically consistent renormalization condition. We find a finite and positive Schwinger current even in the massless limit. This is in contrast to previous calculations in the literature which found a negative IR divergence. We also obtain the first result of the Schwinger current for a non-minimally coupled scalar, including for a conformally coupled scalar which we find has very similar behaviour to the fermion current. Our results may have physical implications for both magnetogenesis and inflationary dark matter production.

Speaker: António Manso (Universidade Coimbra)

61 No Dark Matter Axion During Minimal Higgs Inflation

In this talk, I discuss minimal versions of Higgs inflation (HI) in the presence of a massless QCD axion. While the inflationary energy scale of metric HI is too high to be compatible with isocurvature bounds, it was argued that Palatini HI could evade these constraints. I show, however, that an energy-dependent decay constant enhances isocurvature perturbations, implying that axions can at most constitute a tiny fraction $\sim 10^{-8}$ of dark matter. This conclusion can be avoided in Einstein-Cartan gravity by an additional coupling of the axion to torsion, albeit for a very specific choice of parameters. Analogous constraints as well as the possibility to alleviate them are relevant for all inflationary models with a non-minimal coupling to gravity.

Based on:
C. Rigouzzo, S. Zell, No Dark Matter Axion During Minimal Higgs Inflation, arXiv:2503.XXXXX.

Speaker: Dr Sebastian Zell (Ludwig Maximilian University of Munich)

62 Quantum signatures and decoherence during inflation from deep subhorizon perturbations

In order to shed light on the quantum-to-classical transition of the primordial
perturbations in single field inflation, we investigate the decoherence and associated quantum corrections to the correlation functions of large-scale (superhorizon) scalar curvature perturbations.
The latter are considered as an open quantum system which undergoes quantum decoherence induced by a time-dependent environment of deep subhorizon tensorial modes through the trilinear interactions predicted by General Relativity.
We first prove that, in full generality, a time dependent subhorizon environment can be relevant for decoherence during inflation, by considering derivativeless interactions, which, in our case, give the most important results. For the first time, the time dependence of the environment is properly taken into account by modifying the quantum master equation.
Important non-Markovian effects pop up, instead, when dealing with derivative interactions. Our results show that when considering the interplay between derivativeless and derivative interactions, decoherence is slowed down. This underlines the importance of accounting for all the interactions in open quantum-system calculations in an inflationary setting.
We finally compute the quantum corrections to cosmological correlation functions. We observe a resummation of the quantum corrections to the power spectrum, which is a
general property of quantum master equations. We extend these results to the bispectrum,
showing a decay of this correlation function in time which is analogous to the one found,
previously, for the power-spectrum.

Speaker: Mr Francescopaolo Lopez (SISSA)

Wednesday 28 May

Plenary session: Wednesday morning

63 Gravitational production in the early Universe

Speaker: Yann Mambrini (Paris-Saclay)

64 Dark matter searches through cross-correlations

Speaker: Nicolao Fornengo (Torino)

65 Gamma rays from the Galactic Centre: one excess, two interpretations, many prospects

Speaker: Silvia Manconi (LPTHE)

66 Bound states in theories of (ultra) light dark matter

Speaker: Marco Gorghetto (DESY, Hamburg)

11:00 Coffee

67 Probing dark matter with liquid xenon detectors

Speaker: Laura Baudis (Zürich)

68 New ways of probing QCD axions with supernovae

Speaker: Benjamin Safdi (Berkeley)

12:30 Break for lunch

Baryongenesis

Convener: Luca Vecchi

69 Majoron Dark Matter form exact proton stability

In this talk, we will revisit a class of lepton-flavor non-universal $U(1)$ gauge extensions of the Standard Model that provide a robust mechanism to generate neutrino masses and mixing angles via a high-scale seesaw while ensuring exact proton stability to all orders in the effective field theory. This framework naturally realizes minimal thermal leptogenesis, offering a viable explanation for the observed matter-antimatter asymmetry. A key prediction of this construction is the existence of a light pseudo-Goldstone boson, the majoron. We will explore the potential role of this boson as dark matter and discuss its implications for cosmology and experimental searches.

Speaker: Xavier Ponce Díaz (University of Basel)

70 Genesis of dark matter and baryon asymmetry by majoron

We propose a scenario for cogenesis of baryon asymmetry and dark matter driven by Majoron realizing spontaneous leptogenesis. It can be achieved assuming either an initial kinetic motion or a conventional misalignment with symmetry non-restoration.

Speaker: EUNG JIN CHUN (Korea Institute for Advanced Study)

71 Spontaneous Leptogenesis with sub-GeV Axion Like Particles

A derivative coupling of an axion like particle (ALP) with a B − L current may lead to the baryon asymmetry of the Universe via spontaneous leptogenesis provided a lepton number breaking interaction prevails in thermal equilibrium. Conventionally, such scenario works only for heavy ALPs and high reheating temperature due to the fact that the same lepton number breaking contribution is tied up with neutrino mass generation also. In this work, we propose inert Higgs doublet assisted lepton number violating operator to relieve such tension so as to generate lepton asymmetry (of freeze-in/out type) with a much lower reheating temperature that can accommodate light (sub GeV) ALPs sensitive to current and future ALP searches.

Speaker: Arunansu Sil (IIT Guwahati, India)

72 News on Cold Baryogenesis

The matter-antimatter asymmetry of the Universe represents one of the main open questions in particle physics and cosmology. In this talk, we will present a novel realization of cold baryogenesis, a mechanism involving the formation and decay of topological defects associated with the gauge group of the Standard Model known as SU(2) textures, that relies on the out-of-equilibrium dynamics during a strong first order electroweak phase transition. By performing extensive lattice simulations of the Higgs doublet and gauge field dynamics, we evaluate the related Chern-Simons number production as well as the rate of baryon number violation, as a function of the parameters of the phase transition and the shape of the Higgs potential. We finally provide an estimate for the total baryon asymmetry generated this way.

Speaker: Martina Cataldi (University of Hamburg)

73 Electroweak baryogenesis without electric dipole moments

Electroweak baryogenesis (EWBG) provides an intriguing mechanism to explain the observed baryon asymmetry. Since a new source of CP violation is required to successfully realize this mechanism, the remarkable improvement in experimental bounds on the electric dipole moment (EDM) of electron has put models of EWBG under severe stress.I will discuss a scenario which can robustly avoid the EDM constraints. In this scenario the CP phase needed for EWBG arises predominantly from spontaneous breaking of CP, is present during the electroweak phase transition, and is relaxed to zero today. I will discuss how this scenario can be realized in Composite Higgs models and show that such models considered previously in the literature suffer from a double-tuning problem. I will then present two different classes of models that solve this double-tuning problem.

Speaker: Majid Ekhterachian (EPFL)

74 TBD

Collider Beyond Standard Model Physics

Convener: Stefano Rigolin

75 Underpinnings of CP-Violation at the High-energy Frontier

I will present a general analysis for the discovery potential of CP-violation (CPV) searches in scattering processes at TeV-scale colliders in an effective field theory approach. The CP-violating sector of the SMEFT framework will be examined in some well motivated limiting cases, based on flavour symmetries of the underlying heavy theory. In particular, we show that under naturality arguments of the underlying
new physics (NP) and in the absence of (or suppressed) flavour-changing interactions, there is only a single operator which alters the top-Yukawa coupling, that can generate a non-negligible CPV effect from tree-level SMxNP interference terms. We find, however, that CPV from this operator is expected to be at best of O(1\%) and, therefore, very challenging if at all measurable at the LHC or other future high-energy colliders. We then conclude that a potentially measurable CPV effect, of O(10\%), can arise in high-energy scattering processes ONLY if flavour-changing interactions are present in the underlying NP; in this case a sizable CPV effect can be generated at the tree-level by pure NPxNP effects and not from SMxNP interference. I will provide several examples of CPV at the LHC and at a future e^+e^- collider to support these statements.

---

Based on:
e-Print: 2407.19021 (PLB 2025), e-Print: 2407.19021 (PRL 2023)

Speaker: Dr Shaouly Bar-Shalom (Technion, Israel)

76 Coloured spin-1 resonances in composite Higgs models

Composite Higgs models with an underlying fermionic description predict heavy spin-1 resonances. We study the spin-1 states in a class of realistic models where they come as colour triplets, sextets, and octets. The colour octet vector state is present in all models and mixes with the gluon, allowing for single production at hadron colliders. I will present the phenomenology of these states and derive current bounds from LHC data.

Speaker: Manuel Kunkel (University of Würzburg)

77 The ABC of RPV II: Classification of RPV Signatures from UDD Couplings and their Coverage at the LHC

We perform a detailed study of the current phenomenological status of baryon number violating operators within the framework of the R-parity violating Minimal Supersymmetric Standard Model (RPV-MSSM). This study aims to identify any gaps in the experimental coverage of the RPV landscape. We identify the unique final states for all possible LSPs decaying via four different benchmark UDD operators. Both the direct production of the LSP and its production via gauge-cascades are considered. For each LSP, we assume that only one UDD coupling is non-zero at a time and confront the signals with existing ATLAS and CMS searches implemented in the recasting framework CheckMATE 2. We find that the UDD colored LSP sector is well covered with the mass bounds on the gluino LSP being the strongest, and with possible improvements for some of the right-handed squark LSPs. We also point out that there is limited coverage for electroweakino and slepton LSPs with UDD decays. This limitation may be due to the lack of targeted experimental searches for these specific final states or the appropriate recasting of existing searches.

Speaker: Rhitaja Sengupta (BCTP and Physikalisches Institut der Universität Bonn, Germany)

78 One-loop running in bosonic theories

A general Effective Field Theory (EFT) containing scalars and vectors up to mass dimension six is presented. For such a general theory the complete set of one-loop renormalization group equations (RGEs) is discussed, employing both on-shell unitarity-based and geometric techniques.
The results broadly apply to any EFT with arbitrary gauge symmetry and bosonic degrees of freedom. To illustrate the utility of these results, I will present new results for the running of models containing axion-like particles with CP-violating interactions.

Speaker: Jason Aebischer (CERN)

79 TeV Window to Grand Unification: Higgs's Light Color Triplet Partner

The color-triplet partner of the Higgs doublet, called a $T$-particle, is a universal feature of Grand Unification. It has been shown some time ago that this particle can be accessible for direct production in collider experiments. In this talk we point out that the $T$-particle represents a simultaneous low-energy probe of baryon number violation as well as of the origin of the neutrino mass, linking the mediation of proton decay with oscillations of the neutron into a sterile neutrino. We point out a triple correlation between its collider signatures, proton decay measurements and the searches for the magnetic resonance disappearance of free neutrons in cold neutron experiments. In this way, the $T$-particle can provide a diversity of correlated experimental windows into Grand Unification.

Speaker: Anja Stuhlfauth (Max Planck Institute for Physics)

80 Probing New Physics with Flavor Tagging at FCC-ee

Leveraging recent advancements in machine learning-based flavor tagging, we develop an optimal analysis for measuring the hadronic cross-section ratios $R_b$, $R_c$, and $R_s$ at the FCC-ee during its $WW$, $Zh$, and $t\bar t$ runs. Our results indicate up to a two-order-of-magnitude improvement in precision, providing an unprecedented test of the SM. Using these observables, along with $R_\ell$ and $R_t$, we project sensitivity to flavor non-universal four-fermion (4F) interactions within the SMEFT, contributing both at the tree level and through the renormalization group (RG). We highlight a subtle complementarity with RG-induced effects at the FCC-ee's $Z$-pole. Our analysis demonstrates significant improvements over the current LEP-II and LHC bounds in probing flavor-conserving 4F operators involving heavy quark flavors and all lepton flavors. As an application, we explore simplified models addressing current B-meson anomalies, demonstrating that FCC-ee can effectively probe the relevant parameter space. Finally, we design optimized search strategies for quark flavor-violating 4F interactions.

Speaker: Hector Tiblom (University of Basel)

Gravitational Waves

Convener: Edoardo Vitagliano (University of Padua & INFN Padua)

81 Gravitational waves from current-carrying domain walls

Domain wall (DW) networks may have formed in the early universe following the spontaneous breaking of a discrete symmetry. Notably, several particle physics models predict the existence of current-carrying DWs, which can capture and store particles as zero modes on it. In this study, we demonstrate that gravitational waves (GWs) generated by current-carrying DWs with fermionic zeromodes exhibit a novel feature: an additional peak with a distinct spectral shape in the GW spectrum resembling mountains, arising from metastable topological remnants, which we term ``spherons.'' This distinct signature could be detectable in upcoming GW observatories such as LISA. The results suggest that DW networks in beyond Standard Model scenarios could emit GW signals that are significantly stronger and with greater detectability than previously expected.

Speaker: Yu Hamada (DESY)

82 Probing Axion Inflation via Gravitational-Wave Production

Axion inflation is an extension of the slow-roll paradigm featuring helical gauge-field production with possible consequences for inflationary magnetogenesis, leptogenesis, reheating, and gravitational wave production. I focus on the latter, studying the detectability of gauge-field-induced gravitational waves from axion inflation. For this, I consider two models: the first featuring a „sterile“gauge field, which does not couple to any scalars of fermions, and a more realistic model, where the gauge field in question is the standard-model hypercharge field. The coupling to standard model fermions allows for efficient fermion production via the Schwinger mechanism, drawing energy from the gauge fields and thus impacting the gravitational-wave spectrum.

Speaker: Richard von Eckardstein (Institute for Theoretical Physics - University of Münster)

83 Explaining the PTA signal and dark matter with a conformal dark sector

Strong first-order phase transitions offer a compelling explanation for the stochastic gravitational wave background in the nano-Hertz range measured by pulsar timing arrays (PTA). In this talk, I will consider a classically conformal dark sector in which the breaking of a dark U(1) gauge symmetry gives rise to a gravitational wave background that can fit the PTA data and additionally sources the mass of a stable fermionic sub-GeV dark matter candidate. The model is coupled to the Standard Model via a dark photon mediator which is tightly constrained by laboratory searches. I will discuss these accelerator constraints as well as cosmological constraints coming from the decay of dark Higgs bosons after the phase transition. Finally, I will present the results of a global fit and show that the model has viable parameter space where it fits the PTA data, reproduces the observed relic abundance and avoids all relevant constraints.

Speaker: Carlo Tasillo (Uppsala University)

84 Detecting high frequency gravitational waves at ALPS

Birefringence effects associated with the evolution of the polarization of light have been proposed as a way to detect axion DM. We exploit this method for gravitational wave detection, pointing out how we can describe axions and GW with a unified treatment. We show that by exploiting this method, the optical cavities used by the ALPSII experiment can probe in the near future GWs with frequencies above 100MHz and strain sensitivities of the order of $10^{-14} \sqrt{\mathrm{Hz}}$. Such sensitivity allows the exploration of currently unconstrained parameter space, complementing other high-frequency GW experiments.

Speaker: Luca Marsili (IFIC-University of Valencia)

85 Growth of Cosmic Strings beyond Kination

A novel mechanism to produce a cosmic network of fundamental superstrings based on a time-varying string tension has been recently proposed. It has been found that fundamental (super)strings can grow in a kinating background driven by the volume modulus of Type IIB string compactifications. In this talk, based on arXiv:2503.11293, I will generalise this analysis using dynamical systems techniques. First, I will analyse the cosmological growth of strings with a field-dependent tension in a spatially-flat Universe filled with a perfect fluid, finding the fixed points of the phase space of this system. This machinery is then applied to both fundamental superstrings and effective strings obtained from wrapping $p$-branes on $(p-1)$-cycles. I will show how cosmological growth can be achieved in a non-kinating background, as in scaling fixed points, for fundamental strings as well as for EFT strings arising from wrapped D3- and NS5-branes on fibration cycles.

Speaker: Luca Brunelli (University of Bologna)

86 TBD

Light and dark particles

Convener: Francesco D'Eramo (University of Padua)

87 Early universe neutrino production

We conduct a general study of the various constraints on the existence of primordial high-energy neutrinos (PHENu), emitted as early as the neutrino decoupling era and propagating through the Universe nearly unaltered since their emission. We explore the parameter space in which such neutrinos could be detected and confront our findings with current cosmological and observational constraints.

Speaker: Nicolas Grimbaum Yamamoto (Université Libre de Bruxelles)

88 Dark sector to the rescue of large cosmological neutrino masses

We consider an extended seesaw model which generates active neutrino masses via the usual type-I seesaw and leads to a large number of massless fermions as well as a sterile neutrino dark matter (DM) candidate in the O(10−100) keV mass range. The dark sector comes into thermal equilibrium with Standard Model neutrinos after neutrino decoupling and before recombination via a $U(1)$ gauge interaction in the dark sector. This suppresses the abundance of active neutrinos and therefore reconciles sizeable neutrino masses with cosmology. The DM abundance is determined by freeze-out in the dark sector, which allows avoiding bounds from X-ray searches. Our scenario predicts a slight increase in the effective number of neutrino species $N_{\rm eff}$​ at recombination, potentially detectable by future CMB missions.

Speaker: Drona Vatsyayan (IFIC (UV-CSIC))

89 Revisited axion contribution to dark radiation using momentum-dependent evolution

Axions can be produced via the interactions in the thermal plasma
of the early Universe and their contribution to dark radiation can
modify the cosmological observables and constrain the axion
couplings to SM particles. In my talk I am going to outline an
approach to calculate the axion cosmological abundance that goes
beyond the approximations widely used in the literature on the
topic and demonstrate how it affects the bounds on axion couplings
on the example of axion interactions with leptons.

Speaker: Maxim Laletin (University of Warsaw)

90 Back to the phase space: Thermal axion dark radiation via couplings to standard model fermions

In this talk I present the cosmological consequences of axion interactions with standard model fermions accurately and precisely. Our analysis is entirely based on a phase space framework that allows us to keep track of the axion distribution in momentum space across the entire expansion history. First, we consider flavor-diagonal couplings to charged leptons and quantify the expected amount of dark radiation as a function of the coupling strength. Leptophilic axions are immune from complications due to strong interactions and our predictions do not suffer from theoretical uncertainties. We then focus on flavor-diagonal interactions with the three heavier quarks whose masses are all above the scale where strong interactions become nonperturbative. The top quark case is rather safe because its mass is orders of magnitude above the confinement scale, and the consequent predictions are solid. The bottom and charm masses are in more dangerous territory because they are very close to the QCD crossover. We present a comprehensive discussion of theoretical uncertainties due to both the choice of the scale where we stop the Boltzmann evolution and the running of QCD parameters. Finally, we compute the predicted amount of dark radiation expressed as an effective number of additional neutrino species. We compare our predictions with the ones obtained via standard approximate procedures, and we find that adopting a rigorous phase space framework alters the prediction by an amount larger than the sensitivity of future cosmic microwave background observatories.

Speaker: Alessandro Lenoci (The Hebrew University of Jerusalem)

91 ALP Production from Abelian Gauge Bosons: Beyond Hard Thermal Loops

Previous studies on the production of feebly interacting particles have encountered challenges due to negative interaction rates at soft momenta. We resolve this issue by investigating the thermal production of Axion-Like Particles (ALPs) from the freeze-in mechanism via feeble interactions with U(1) gauge fields, employing the full 1PI-resummed gauge boson propagator. This approach ensures a consistent treatment across all momentum scales, avoiding the need for matching or subtraction techniques.

Our analysis confirms that the ALP production rate remains positive throughout and identifies new production channels at soft momentum $(p\le g^2T)$. These results refine the predicted thermal ALP abundance and momentum distribution, providing important input for structure formation constraints on keV-mass ALP dark matter. More broadly, our approach offers a systematic and physically consistent framework for addressing infrared effects in feebly interacting particle production.

(Based on arXiv:2502.01729v1)

Speaker: Cristina Puchades Ibáñez (JGU)

92 TBD

17:00 Social excursion

Thursday 29 May

Masiero Fest

93 Reflections on BSM physics, about half a century later

Speaker: Riccardo Barbieri (SNS Pisa)

94 From SUSY to the Coq au vin and Beyond

Speaker: Guido Martinelli (Sapienza)

95 Higgs compositeness in supersymmetric models

Speaker: Gian Francesco Giudice (CERN)

96 Antonio & the Dark Universe

Speaker: Laura Covi (Göttingen)

11:00 Coffee

Plenary session: Thursday morning

97 Black Holes and Symmetries

Speaker: Antonio Riotto (Geneva)

98 Model independent searches of New Physics from the Large Scale Structure

Speaker: Massimo Pietroni (Parma)

12:30 Break for lunch

Axions

Convener: Edoardo Vitagliano (University of Padua & INFN Padua)

99 Kinetic Axion from non-minimally coupled PQ Field

Axion Kinetic Misalignment can be generated by higher-order operators that explicitly break the PQ symmetry at very high energies. This results in a kick in the angular direction of the PQ field, causing a delay in the onset of axion oscillations. For the higher-order operator to be relevant, the PQ radial mode must reach very high values. We explore the possibility that a non-minimally coupled PQ field, with a
term, combined with a stiff era, can generate the exact initial conditions for a Kinetic Misalignment Mechanism.

Speaker: Riccardo Natale (DESY)

100 Searching for Axion Dark Matter with Radio Telescopes

The QCD axion, originally proposed to resolve the strong CP problem, is also a compelling dark matter (DM) candidate. In strong magnetic fields, such as those surrounding neutron stars, axions can convert into photons, potentially generating detectable radio signals. This axion-photon coupling offers a unique avenue for experimental searches in a well-defined mass range. In this seminar, I will present an observational study using the Green Bank Telescope (GBT) to search for transient radio signals from axion-photon conversion. Focusing on the core of Andromeda, we employ the VErsatile GBT Astronomical Spectrometer (VEGAS) and the X-band receiver (8–10 GHz) to probe axions with masses between 33 and 42 μeV, achieving a mass resolution of 3.8 × 10^-4 μeV. We describe our observational strategy and analysis techniques, which reach an instrumental sensitivity of 2 mJy per spectral channel. While no candidate signals exceeding the 5σ threshold were detected, I will discuss future improvements, including expanding the search to additional frequency bands and refining theoretical models, to strengthen constraints on axion DM scenarios. Based on 2407.13060, 2011.05378, 2011.05377, and ongoing work.

Speaker: Luca Visinelli (TDLI)

101 A Systematic Approach to Axion Production at Finite Density

As an elegant solution to the strong CP problem and promising dark matter candidate, the QCD axion is one of the best motivated particles beyond the SM. On the phenomenological side, it is extremely predictive as all its couplings to SM particles as well as its mass is determined by a single scale, the axion decay constant. The hunt for the QCD axion, both with terrestrial experiments as well as astrophysical observables, has exploded in the last years. As of today, astrophysical observations, such as neutron star cooling and energy loss from supernovae, place the strongest bounds.
In this talk, I will show that astrophysical bounds depend on a non-trivial momentum dependence of the axion-nucleon production in zero- as well as in finite density environments. This dependence is induced by one-loop corrections to that can be systematically calculated within the framework of chiral perturbation theory, both at zero density and in thermal field theory. As a consequence, the supernova bound is strengthened and the momentum dependence further allows us to constrain large parts of parameter space of the axion neutron coupling. I will talk about the current status of this systematic calculation systematically in chiral perturbation theory and elaborate how our findings compare to more phenomenological approaches in literature.
Additionally, I will talk about the model independent axion production mechanism in supernova, leading to a orders of magnitude stricter bound than in current literature.

Speaker: Michael Stadlbauer (Max-Planck-Institut for Physics/TU Munich)

102 The Gauge Axion

The most commonly accepted solution of the strong CP problem in QCD is the Axion, which in the majority of formulations is taken to be the Goldstone of a spontaneously broken, global $U(1)$-symmetry, the Peccei-Quinn symmetry. However, there exists an alternative formulation of the axion solution, a so-called "gauge axion". In this formulation the axion emerges as an intrinsic part of the QCD gauge redundancy, without the need for a global symmetry. In contrast with the Peccei-Quinn axion, by the power of gauge redundancy, the gauge axion has exact quality to all orders of the operator expansion. We discuss implications of this scenario, focusing on cosmic strings, domain walls and their potential consequences.

Speaker: Lucy Komisel (Max-Planck Institute for Physics, Munich)

103 Interplay of vertical and horizontal gauge symmetry for a high-quality axion

We present an axion model based on the Pati-Salam group, where $\mathrm{SU}(3)_{f_R}$ (part of flavor symmetry) has also been gauged. The choice of field content ensures a careful interplay of the two symmetries, such that an accidental global $\mathrm{U}(1)$ Peccei-Quinn (PQ) symmetry emerges. The resulting axion is of high quality for the breaking scale in a certain range, and the model's Yukawa sector is realistic. A characteristic feature of having both a vertical (Pati-Salam) and horizontal (flavor) symmetry are anomalons --- parametrically light fermions required to cancel gauge anomalies. We analyze their interplay with neutrinos and their production in the early universe. Their effect on $\Delta N_{\text{eff}}$ could serve as a low energy probe for the underlying dynamics of PQ quality.

Speaker: Vasja Susič (Laboratori Nazionali di Frascati (LNF), INFN)

Flavor and Intensity Physics

Convener: Luca Vecchi

104 Discovering LFV at a Future Muon Collider: A SMEFT Approach

The strongest current bounds on lepton flavor violation (LFV) come primarily from low energy precision observables. While these experiments are expected to improve substantially in the next decade, there are cases where a muon collider could complement existing searches. In this talk, we utilize a SMEFT approach to explore the complementarity of muon colliders with low energy experiments for exploring LFV. We find a muon collider could probe regions of parameter space beyond what is explored with low energy experiments, including blind spots that low energy experiments are not sensitive to.

Speaker: Katherine Fraser (UC Berkeley/LBNL)

105 Flavour Deconstructing the Composite Higgs

In the first part of the talk, we will introduce the main model building ideas, namely flavour non-universality and Higgs compositeness, that are central to our model, as well as the theoretical and experimental motivations for exploring these BSM avenues. In the second part of the talk, we present a flavour non-universal extension of the Standard Model combined with the idea of Higgs compositeness. At the TeV scale, the electroweak gauge symmetry is assumed to act in a non-universal manner on light- and third-generation fermions, while the Higgs emerges as a pseudo Nambu-Goldstone boson of a spontaneously broken global symmetry. The flavour deconstruction implies that the couplings of the light families to the composite sector are suppressed by powers of a heavy mass scale, explaining the flavour puzzle. We present a detailed analysis of the radiatively generated Higgs potential, showing how this intrinsically-flavoured framework has the ingredients to justify the unavoidable tuning in the Higgs potential necessary to separate electroweak and composite scales. The model is compatible with current experimental bounds and predicts new states at the TeV scale, which are within the reach of near future experimental searches. Arxiv: 2407.10950

Speaker: Marko Pesut (University of Zurich)

106 Searches for dark sector particles at Belle and Belle II

The Belle and Belle II experiment have collected samples of $e^+e^-$
collision data at centre-of-mass energies near the $\Upsilon(nS)$
resonances. These data have constrained kinematics and low
multiplicity, which allow searches for dark sector particles in the mass
range from a few MeV to 10~GeV. Using a 426 fb$^{-1}$ sample collected
by Belle~II, we search for inelastic dark matter accompanied by a dark
Higgs. Using a 711 fb$^{-1}$ sample collected by Belle, we search for
$B\to h + \mathrm{invisible}$ decays, where $h$ is a $\pi$, $K$, $D$,
$D_{s}$ or $p$, and $B\to Ka$, where $a$ is an axion-like particle.

Speaker: Steven Robertson (IPP / UofA)

107 Lepton Flavor Violating decays in a realistic U(2) flavor model

Building on the realistic U(2) flavor model proposed a few years ago by Linster and Ziegler, we conduct a comprehensive study of possible neutrino mass textures arising from the seesaw mechanism. We identify a set of viable models that provide an excellent fit to low-energy Standard Model flavor observables including neutrinos. Additionally, within an Effective Field Theory framework, we analyze lepton flavor-violating decays in these models and examine their implications for the muon anomalous magnetic moment.

Speaker: Simone Marciano (IFIC - CSIC - University of Valencia)

108 Probing Dark Sectors with EDMs

Dark sectors provide beyond Standard Model scenarios which can address unresolved puzzles, such as the observed dark matter abundance or the baryon asymmetry of the Universe. A naturally small portal to the dark sector is obtained if dark-sector interactions stem from a non-Abelian hidden gauge group that couples through kinetic mixing with the hypercharge boson. In this work, we investigate the phenomenology of such a portal of dimension five in the presence of CP violation, focusing on its signatures in fermion electric dipole moments. We show that, currently unbounded regions of the parameter space from dark photon searches can be indirectly probed with upcoming electron dipole moment experiments for dark boson masses in the range $1-100$ GeV. We also discuss two particular scenarios where a $SU(2)_D$ dark gauge group spontaneously breaks into either an Abelian $U(1)_D$ or nothing. In both cases, we show that potentially observable electron dipole moments can be produced in vast regions of the parameter space compatible with current experimental constraints and observed dark matter abundance.

Speaker: Marco Ardu (University of Valencia & IFIC)

Reheating and Baryongenesis

Convener: Antonio Masiero (DFA UniPD)

109 Non-singular solutions to the Boltzmann equation with a fluid Ansatz

Cosmological phase transitions can give rise to intriguing phenomena, such as baryogenesis and stochastic gravitational wave backgrounds, due to nucleation and percolation of vacuum bubbles in the primordial plasma. A key parameter for predicting the amount of these relics is the bubble wall velocity, whose computation relies on solving the Boltzmann equations of the various species in the plasma along the bubble profile. One approach to this task relies on adopting a fluid Ansatz for the non-equilibrium distribution function, which greatly simplifies the collision terms and makes the system more tractable when a linearization is performed on the non-equilibrium fluctuations. In this Ansatz one typically performs a separation of what is called the background properties of the plasma, and the non-equilibrium fluctuations around this background. Clearly, an appropriate choice of background is essential to ensure that the non-equilibrium fluctuations will remain sufficiently small to grant the application of the linearization procedure. However, the recent literature on this approach typically modelled the background as constant, leaving all the spatial-dependence arising from equilibrium effects to be described as fluctuations of the light species. This led to a breakdown of the linear approximation when the wall approached the speed of sound, making the solutions singular. In this work we solve this issue by reparameterizing the fluid Ansatz to include these equilibrium fluctuations into the background (which then becomes spatially-dependent), rather than in the fluctuations. This leads to a modification of the Boltzmann equation, and we show that all terms that would give rise to a singularity now vanish. We recalculate the different contributions to the counter-pressure of the plasma on the expanding wall, and discuss their relative importance. The Standard Model with a low cutoff is chosen as benchmark model and results are shown for different values of the cutoff scale. Our finding indicate that non-equilibrium effects are typically non-negligible for the computation of the wall velocity.

Speaker: Gláuber Dorsch (Universidade Federal de Minas Gerais (UFMG), Brazil)

110 Dynamical origin of neutrino masses and dark matter from a new confining sector

A dynamical mechanism, based on a confining non-Abelian dark symmetry, which generates Majorana masses for hyperchargeless fermions, is proposed. We apply it to the inverse seesaw scenario, which allows us to generate light neutrino masses from the interplay of TeV-scale pseudo-Dirac mass terms and a small explicit breaking of lepton number. A single generation of vectorlike dark quarks, transforming under a
SU(3)D gauge symmetry, is coupled to a real singlet scalar, which serves as a portal between the dark quark condensate and three generations of heavy sterile neutrinos. Such a dark sector and the Standard Model (SM) are kept in thermal equilibrium with each other via sizable Yukawa couplings to the heavy neutrinos. In this framework, the lightest dark baryon, which has spin 3/2 and is stabilized at the renormalizable level by an accidental dark baryon number symmetry, can account for the observed relic density via thermal freeze-out from annihilations into the lightest dark mesons. These mesons, in turn, decay to heavy neutrinos, which produce SM final states upon decay. This model may be probed by next generation neutrino telescopes via neutrino lines produced from dark matter annihilations.
e-Print: 2403.17488 [hep-ph]
journal: Phys.Rev.D 110 (2024) 3, 035011

Speaker: Maximilian Berbig (IFIC & University of Valencia)

111 Baryogenesis from bubble collisions

In this talk I will consider models connecting baryogenesis with first order phase transition. In particular, I will elaborate on scenarios where the required amount of CP-violation originates from the production of heavy particles after true vacuum particles collide. I will focus on the case when both heavy particles are produced on-shell as well as the opposite regime when one of the heavy particles is produced off-shell, subsequently decaying to light Standard Model states. I will elaborate on the phenomenological implications of both scenarios.

Speaker: Kristjan Müürsepp (NICPB, Tallinn and LNF-INFN, Frascati)

112 Minimal Electroweak Baryogenesis with Domain Walls

We propose a novel mechanism for Electroweak Baryogenesis (EWBG) within the real singlet extension of the Standard Model with an approximate ℤ2 symmetry. Domain walls associated with the spontaneous breaking of the ℤ2 symmetry feature restored (or weakly broken) EW symmetry in their core. In combination with a CP-violating source, the walls sweeping through space generate the baryon asymmetry below the temperature of the EW phase transition.
We identify the key conditions on the domain wall profiles and evolution, necessary for the realisation of the proposed mechanism. Eventually, we find the relevant parameter space to span singlet masses from sub-eV to 15 GeV, accompanied by a non-vanishing mixing with the Higgs boson. Unlike the standard realisation of EWBG in the minimal singlet-extended SM, which is notoriously difficult to test, this scenario can be probed by a wide range of existing and upcoming experiments, including fifth force searches, rare meson decays, and EDM measurements.
Based on arXiv:2412.10495.

Speaker: Jacopo Azzola (Technische Universität München)

113 Search for Baryogenesis and Dark Matter in $B$-meson decays at $BABAR$

We present the most recent $BABAR$ searches for reactions that could simultaneously explain the presence of dark matter and the matter-antimatter asymmetry in the Universe. This scenario predicts exotic $B$-meson decays of the kind $B\to\psi_{D} {\cal B}$, where $\cal{B}$ is an ordinary matter baryon (proton, $\Lambda$, or $\Lambda_c$) and $\psi_D$ is a dark-sector anti-baryon, with branching fractions accessible at the $B$ factories. The hadronic recoil method has been applied with one of the $B$ mesons from $\Upsilon(4S)$ decay fully reconstructed, while only one baryon is present in the signal $B$-meson side. The missing mass of signal $B$ meson is considered as the mass of the dark particle $\psi_{D}$. Stringent upper limits on the decay branching fraction are derived for $\psi_D$ masses between 0.5 and 4.3 GeV/c$^2$. The results are based on the full data set of about 470 million $B-\overline B$ pairs collected at the $\Upsilon(4S)$ resonance by the $BABAR$ detector at the PEP-II collider

Speaker: Isabella Garzia (INFN Sezione di Ferrara and University of Ferrara)

Reheating and Big-Bang Nucleosynthesis

Convener: Francesco D'Eramo (University of Padua)

114 BBN constraints on massive relics decaying into neutrinos.

Constraints on dark sector particles decaying into neutrinos typically focus on their impact on the effective number of relativistic species, Neff, in the early Universe. However, for heavy relics with longer lifetimes, constraints mainly arise from the photo-disintegration and hadro-disintegration of primordial abundances. The high-energy neutrinos injected by the decay can interact with both the thermal neutrinos and other high-energy neutrinos. Among these interactions, annihilations into electromagnetic and hadronic particles will induce electromagnetic and hadronic cascades that affect the abundances of the already formed light elements. In this work, we present new constraints on these dark sector particles. We find improved bounds on the particle's lifetime, abundance, and mass.

Speaker: Sara Bianco (DESY-T)

115 Current constraints on very low reheating temperatures

We present an updated analysis of cosmological models with very low reheating scenarios, where TRH∼O(MeV). Our study includes a more precise computation of neutrino distribution functions, leveraging the latest datasets from cosmological surveys. We perform a joint analysis that combines constraints from Big Bang Nucleosynthesis, the Cosmic Microwave Background, and galaxy surveys, alongside separate investigations of these datasets, carefully assessing the impact of different choices of priors. At the 95% confidence level, we establish a lower bound on the reheating temperature of TRH > 5.96 MeV, representing the most stringent constraint to date. Based on https://arxiv.org/abs/2501.01369

Speaker: Sergio Pastor (IFIC, CSIC-Univ. Valencia)

116 Lepton Flavour Asymmetries: from the early Universe to BBN

In this talk I discuss the constraints imposed by BBN and CMB observations on primordial lepton flavour asymmetries with vanishing total lepton number. I show that solving the momentum averaged quantum kinetic equations describing neutrino oscillations and interactions is an accurate approximation to the full momentum-dependent system, and the results reveal a rich flavour structure in stark contradiction to the assumption of simple flavour equilibration. In particular, the appearance of non-adiabatic MSW transitions lead to especially strong or weak washouts — a phenomenon for which I will present the first analytical understanding in the standard case with three active neutrinos. We further encounter (i) a particular direction in flavour space, in which the flavour equilibration is efficient and primordial asymmetries are essentially unconstrained and (ii) a minimal washout factor yielding a conservative estimate for the allowed primordial asymmetries in a generic flavour direction. I discuss the implications of the resulting BBN and CMB constraints on models of first-order QCD phase transition facilitated by large lepton asymmetries as well as baryogenesis from large and compensated asymmetries.

Speaker: Mario Fernandez Navarro (Univeristy of Glasgow)

117 Thermal Effects in Freeze-In Dark Matter Production

One of the many compelling mechanisms for dark matter production is the freeze-in mechanism. In contrast to the more widely studied freeze-out scenario, freeze-in production is sensitive to thermal corrections, which can significantly impact the predicted dark matter abundance.

In this talk, we investigate the impact of thermal effects on dark matter production. We consider a model featuring a feebly interacting real scalar and a vector-like mediator. In particular, we analyze the contribution of multiple soft scatterings, an effect known as the Landau-Pomeranchuk-Migdal effect. We find that including this effect can modify the predicted dark matter relic abundance by up to 20%. In addition, we analyze the theoretical uncertainties arising from different approaches.

Speaker: Maria Jose Fernandez Lozano (JGU Mainz)

118 Dark matter in QCD-like theories with a theta vacuum: cosmological and astrophysical implications

QCD-like theories in which the dark matter (DM) of the Universe is hypothesized to be a thermal relic in the form of a dark pion has been extensively investigated, with most studies neglecting the CP-violating
θ-angle associated with the topological vacuum. We point out that a non-vanishing θ could potentially trigger resonant number-changing processes giving rise to the observed relic density in agreement with perturbative unitarity as well as observations of clusters of galaxies. This constitutes a novel production mechanism of MeV DM and an alternative to those relying on the Wess-Zumino-Witten term. Moreover, for specific meson mass spectra, similar resonant scatterings serve as a realization of velocity-dependent self-interacting DM without a light mediator. Explicit benchmark models are presented together with a discussion of possible signals, including gravitational waves from the chiral phase transition associated with the dark pions.

Speaker: giacomo landini (IFIC and Universidad de Valencia)

16:00 Coffee Break

Astroparticle detection

Convener: Francesco D'Eramo (University of Padua)

119 Experimental monopole bounds updated by models of acceleration in cosmic fields

Magnetic Monopoles are accelerated by cosmic magnetic fields in relation to their mass and number, due to back-reaction. After recent experimental lower limits on the intergalactic magnetic fields (IGMFs), we have revisited a coherent acceleration scenario in which monopoles are accelerated in intergalactic and Galactic magnetic fields before reaching the Earth (Phys.Dark Univ. 46 (2024)). This, for various fields realizations, allow us to recast several experimental limits on monopoles, from IceCube, Pierre Auger Observatory, MACRO, and seed Parker bounds, among others, in terms of monopole mass, while normally seen in function of the speed. We see that experimental limits are sensitive to acceleration in the IGMF in some conditions, so the argument can be reversed and magnetic monopoles limits can also be used to constraints the IGMF. Our scenario can be easily adapted to any different model of cosmic magnetic fields

Speaker: Michele Doro (Dipartimento di Fisica e Astronomia Università di Padova)

120 Hunting for Relativistic Axions with the Square Kilometer Array

Axion-like particles (ALPs) are weakly interacting particles that are predicted to exist by many beyond standard model theories. A large number of experiments have been constructed or are under construction to search for these ALPs both directly and indirectly (through astrophysical or cosmological observations). In this work we have studied how photon signals originating from the oscillation of relativistic ALPs, produced from the decay of a cosmologically stable scalar DM of mass $10^{−7}$ − $10^{−2}$ eV inside a dwarf spheroidal galaxy (dSph), can be detected by the upcoming radio telescope Square Kilometer Array (SKA). We show that observation of dSphs with the SKA can help us put strong bounds on the ALP-photon coupling in the ALP mass range $m_a < 10^{−12}$ eV. We further show, for a fixed ALP mass and coupling, SKA observation can also help us put bounds in the DM mass vs lifetime parameter space, thus opening up a new avenue in the indirect detection of DM.

Speaker: Tanmoy Kumar (Indian Association for the Cultivation of Science)

121 On the fate of evaporating black holes: how the burden of their memory stabilizes them

The “memory burden” effect describes how an object’s stored information resists its own decay. This effect is especially pronounced in “saturons”—systems with maximal entropy consistent with unitarity—of which black holes are prime examples. I will show how this memory burden can halt Hawking evaporation, stabilizing black holes against complete decay. Importantly, this mechanism is not limited to gravitational systems: it also appears in renormalizable field theories. To illustrate its broader relevance, I will present a soliton model that shares key features with black holes and is similarly stabilized by its memory content. Finally, I will discuss unique phenomenological implications and potential observational signatures, particularly relevant for dark matter scenarios

Speaker: Dr Michael Zantedeschi (INFN, Sezione di Pisa)

122 Could We Observe an Exploding Black Hole in the Near Future?

Observation of an exploding black hole would provide the first direct evidence of primordial black holes, the first direct evidence of Hawking radiation, and definitive information on the particles present in nature. However, indirect constraints suggest that direct observation of an exploding Schwarzschild black hole is implausible. We introduce a dark-QED toy model consisting of a dark photon and a heavy dark electron. In this scenario a population of light primordial black holes charged under the dark u(1) symmetry can become quasi-extremal, so they survive much longer than if they were uncharged, before discharging and exhibiting a Schwarzschild-like final explosion. We show that the answer is "yes", in this scenario the probability of observing an exploding black hole over the next 10 years could potentially be over 90%.

Speaker: Quim Iguaz Juan (UMass Amherst)

123 Cosmic Colliders: High Energy Physics with First-Order Phase Transitions

Vacuum decay through runaway first order phase transitions presents a unique opportunity for particle physics and cosmology: collisions of vacuum bubbles can act as cosmic scale high energy colliders close to the Planck scale, providing access to high energy physics far beyond any temperature or energy scale ever reached in the history of our Universe. This talk will cover recent developments and challenges in the physics for understanding such frameworks, as well as their broad applications for particle physics and cosmology, from dark matter to leptogenesis to gravitational waves.

Speaker: Bibhushan Shakya (DESY)

Dark Matter and Dark Energy

Convener: Antonio Masiero (DFA UniPD)

124 Extended Effective Field Theory of Dark Energy

We continue our studies of the ghost condensate (GC) with sixth-order dispersion relation. Contrary to the GC with quartic dispersion relation, we find that the correction to the Newtonian potential explicitly depends on the space and time dependence of matter density. At late times when the Newtonian potential becomes time-independent, one obtains similar oscillatory behavior at the distance $\frac{M_{\rm Pl}}{M^2}$, but this time at the time scale $\frac{M^4}{{M_{\rm Pl}}^3}$, where $M^2$ is the ghost field velocity.
We also show that the speed of the gravitational wave is modified in a frequency-dependent manner at momenta close to $\frac{M_{\rm Pl}}{\sqrt{|\sigma_1|}}$, where $\sigma_1$ is the coefficient of $\gamma^{ij} \nabla_i K_{lr} \nabla_j K^{lr}$ operator in the unitary gauge action.

Speaker: Amjad Ashoorioon (School of Physics, Institute for Research in Fundamental Sciences (IPM))

125 FIMP dark matter from flavon portals

We investigate the phenomenology of a non-thermal dark matter (DM) candidate in the context of flavor models that explain the hierarchy in the masses and mixings of quarks and leptons via the Froggatt-Nielsen (FN) mechanism. A flavor-dependent U(1)FN symmetry explains the fermion mass and mixing hierarchy, and also provides a mechanism for suppressed interactions of the DM, assumed to be a Majorana fermion, with the Standard Model (SM) particles, resulting in its FIMP (feebly interacting massive particle) character. Such feeble interactions are mediated by a flavon field through higher dimensional operators governed by the U(1)FN charges. We point out a natural stabilizing mechanism for the DM within this framework with the choice of half-integer U(1)FN charge n for the DM fermion, along with integer charges for the SM fermions and the flavon field. In this flavon portal scenario, the DM is non-thermally produced from the decay of the flavon in the early universe which becomes a relic through the freeze-in mechanism. We explore the allowed parameter space for this DM candidate from relic abundance by solving the relevant Boltzmann equations. We find that reproducing the correct relic density requires the DM mass to be in the range (100 − 300) keV for n = 7.5 and (3 − 10) MeV for n = 8.5 where n is the U(1)FN charge of the DM fermion.

Speaker: Nandini Das (School of Physical Sciences, Indian Association for the Cultivation of Science)

126 Generating GeV-scale Dark Matter masses from the QCD vacuum

The comparable abundances of dark matter and baryons, known as the Dark Matter-Baryon coincidence, call for an explanation that relates the dark sector to the QCD sector. In models of Asymmetric Dark Matter, the number densities of both sectors are naturally similar. However, a complete solution should also include a mechanism to ensure comparable masses. In this talk, I will present a new solution where the dark matter mass is generated from the QCD vacuum, setting it at the GeV scale as baryon masses. The UV completion with chiral strong dynamics and relevant phenomenology from the dark QCD sector will also be discussed.

Speaker: Yi Chung (Max-Planck-Institut für Kernphysik)

127 Light Dark Matter at LDMX: Dipole Emission and Global Fits

Sub-GeV dark matter (DM) has been gaining significant interest in recent years, since it can account for the thermal relic abundance while evading nuclear recoil direct detection constraints. Light DM does not carry enough momentum to be probed via nuclear recoils; other search strategies such as direct detection via electron recoils and accelerators are ideal. We focus on accelerator experiments, considering two main directions.
First, we investigate the vast theory potential of accelerator based experiments, in particular fixed target experiments such as LDMX. We consider dark photons with additional loop induced interactions, namely higher order dark electromagnetic moments – leading to different signatures at LDMX than the ordinary kinetic mixing interaction.
Secondly, we compare constraints from laboratory experiments, and from astrophysical and cosmological observations with the predictions of two sub-GeV DM models within frequentist and Bayesian global analyses using GAMBIT. We infer the regions in parameter space preferred by current data, and compare with projections of near-future experiments, providing a status update to sub-GeV DM.

Speaker: Taylor Gray (Chalmers University of Technology)

128 Gravothermalizing into Primordial Black Holes

Very little is known about the universe’s history from after the end of inflation until the Big Bang nucleosynthesis, which spans more than $10^{39}$ orders of magnitude in time scales. In this work, we show that if there was a long period of matter domination in this unknown period, and if the particle causing the matter domination has moderate self-interactions, the matter particles can undergo gravothermal collapse to form exotic states as primordial black holes (PBHs), boson stars, and cannibal stars. We found that for some choice of parameters, our model can predict an amount of PBHs surviving until today comparable to dark matter. For an optimistic estimate of PBH abundance, we also find that PBHs with masses less than $10^9$ g can reheat the universe before BBN. From the bounds on the PBH abundance, we also constrain the models in a large range of parameters.

Speaker: Daniele Perri (Warsaw University)

Gravitational Waves and Scalar perturbations

Convener: Luca Di Luzio (INFN Padova)

129 Optical gravitational waves as signals of Gravitationally-Decaying Particles

Long-lived heavy particles present during the big bang could have a decay channel opened by gravitons. Such decays can produce gravitational waves with large enough abundance to be detectable, and a peculiar narrow spectrum peaked today around optical frequencies. We identify which particles can decay in one or two gravitons. The maximal gravitational wave abundance arises from theories with extra hidden strong gauge dynamics, such as a confining pure-glue group. An interesting abundance also arises in theories with perturbative couplings. Future observation might shed light on early cosmology and allow some spectroscopy of sub-Planckian gravitationally-decaying particles, plausibly present in a variety of theories such as gauge unification, supersymmetry, extra dimensions, strings.

Speaker: Alessandro Strumia (Unipi)

130 High Frequency Gravitational Wave Bounds from Galactic Neutron Stars

High-frequency gravitational waves (HFGWs) provide a unique probe into early Universe physics and exotic astrophysical objects. While current and future gravitational wave detectors work on lower frequencies, graviton-to-photon conversion in strong magnetic fields offers a complementary detection method suitable for HFGW. Neutron stars, with their extreme magnetic fields ($\sim 10^{13}$ Gauss), serve as natural laboratories for this process. For the first time, this study calculates, using realistic models of the Milky Way's NS population, the expected photon flux induced by the conversion of an isotropic stochastic gravitational wave background in the neutron star magnetosphere. We compare this photon flux to the observed flux from several telescopes and derive constraints on the stochastic gravitational wave background in the $10^8 - 10^{25}$ Hz range, finding competitive limits, particularly between $10^8 - 10^{12}$ Hz. Therefore, the galactic NS population is a powerful tool to probe the presence of an HFGW background.

Speaker: Francesco Costa (IPNP, Charles University)

131 No scalar-induced GW signal from PBH evaporation

We discuss the scalar-induced-gravitational-wave (SIGW) signal from primordial black hole (PBH) evaporation. In the monochromatic scenario, a significant signal is generated by the poltergeist mechanism as a result of a sudden transition from matter to radiation dominance. Non-trivial mass distributions affect this mechanism by prolonging the transition period. We show that for realistic mass distributions, commonly assumed from superhorizon formation, no signal can be expected in any part of the PBH parameter space in any of the upcoming GW experiments. We pay particular attention to the validity of the linearity of the perturbation theory, the cutoff of the curvature power spectrum due to diffusion damping, and curvature sources from adiabatic and isocurvature initial conditions.

Speaker: Nicholas Leister (Johannes Gutenberg-Universität Mainz)

132 The role of the counterterms in the conservation of superhorizon curvature perturbations at one loop

Recently, several papers have claimed that superhorizon curvature perturbations are not conserved at the one-loop level in single-field inflation models if there is a transient ultra-slow-roll period. In this talk, I point out that the contributions from the counterterms were overlooked in the recent papers. I show that the counterterm contributions play a crucial role in canceling the one-loop power spectrum of superhorizon curvature perturbations in the comoving gauge. This talk will be based on arXiv:2502.12112.

Speaker: Keisuke Inomata (Johns Hopkins University)

133 Spectral behavior of scalar fluctuations generated by gravity during inflation and reheating

In this talk, we investigate the spectral behavior of scalar fluctuations generated by gravity during inflation and reheating, employing a non-perturbative Bogoliubov treatment within the framework of gravitational reheating. We obtain both long and short-wavelength spectra. It highlights that the spectral index in the IR regime varies depending on the post-inflationary equation of state (EoS) for a wide range of momenta and masses. In the UV regime, we identify high-frequency oscillations in the spectrum due to the inflaton background dynamics during reheating, which leads to interference in generating the modes. Remarkably, we found that for a large range of EoS, the spectral index in the UV is independent of the EoS. We corroborate our results by comparing the Bogoliubov treatment with perturbative methods, solving the Boltzmann equation. We show agreement across all EoS in the UV regime for the two approaches. Finally, we discuss the gravitational reheating scenario and address constraints from primordial gravitational wave overproduction, finding that successful gravitational reheating is achievable for sufficiently high EoS.

Speaker: Simon Cléry (Technical University of Munich (TUM))

Model Building

Convener: Luca Vecchi

134 Fractionally charged particles of the Standard Model

The Standard Model gauge group that describes strong and electroweak interactions in nature is based on the universal cover SU(3)_c x SU(2)_L x U(1)_Y, which can be moded by discrete symmetries Z_p, where p={1, 2, 3, 6}. Each of these possibilities recovers the usual Standard Model matter fields but also allows for new distinct representations. We will explore the allowed hypercharge spectra of each case and discuss the phenomenological implications that arise in our attempt to "nail down" the actual Standard Model gauge group.

Speaker: Despoina Dimakou (Institute of Particle Physics and Phenomenology, Durham University)

135 Cosmological selection of a small weak scale from large vacuum energy: a minimal approach

We present a minimal cosmological solution to the hierarchy problem. Our model consists of a light pseudoscalar and an extra Higgs doublet in addition to the Standard Model field content. We consider a landscape of vacua with varying values of the electroweak vacuum expectation value (VEV). The vacuum energy in our model peaks in a region of the landscape where the electroweak VEV is non-zero and much smaller than the cutoff. During inflation, due to exponential expansion, such regions of the landscape with maximal vacuum energy dominate the universe in volume, thus explaining the observed smallness of the electroweak scale with respect to the cutoff. The pseudoscalar potential in our model is that of a completely generic pseudogoldstone boson---not requiring the clockwork mechanism---and its field value never exceeds its decay constant or the Planck scale. Our mechanism is robust to the variation of other model parameters in the landscape as the electroweak VEV is varied. It also predicts a precise and falsifiable relationship between the masses and couplings of the different Higgs boson mass-eigenstates. Moreover, the pseudoscalar in our model can account for the observed dark matter relic density.

Speaker: Susobhan Chattopadhyay (Tata Institute of Fundamental Research (TIFR), Mumbai)

136 Dark pions at next-to-leading order

QCD-like theories are of interest in various areas of beyond-Standard-Model phenomenology, including composite Higgs models and strongly interacting pionic dark matter. The low-energy effective field theories provide a framework for describing the dynamics of such strongly coupled gauge theories.
In this work, we present next-to-leading order (NLO) expressions for masses, condensates, decay constants, and scattering amplitudes in the chiral expansion of QCD-like theories with $N_f = 2$ quarks of different masses in both real and pseudoreal representations. These results offer a systematic approach for analyzing the impact of NLO corrections in such theories.
We apply the NLO formulas for masses, decay constants, and the scattering length to fit existing lattice spectroscopic and scattering data, extracting the NLO low-energy constants (LECs) of the $SU(4) \to Sp(4)$ theory. With these estimates, we refine previous NLO analyses and confirm that NLO contributions play a crucial role in determining the viable parameter space for strongly interacting massive particle (SIMP) dark matter.

Speaker: Daniil Krichevskiy (University of Stavanger)

137 Vacuum Metastability from Axion-Higgs Criticality

Self-organised criticality, realised through cosmological dynamics in the early universe, is an alternative paradigm for addressing the electroweak hierarchy problem. In this scenario, an unnaturally light Higgs boson is the result of dynamics driving the electroweak vacuum towards a near-critical metastable point where the Higgs mass is bounded from above by the vacuum instability scale. To lower the vacuum instability scale close to the weak scale, previous realisations of this mechanism introduced new vector-like fermions coupled to the Higgs. Here we show that an Axion-Like Particle (ALP) coupling to the Higgs is an alternative possibility for achieving criticality with another well-motivated and naturally light candidate for new physics, thus leading to an entirely different set of testable phenomenological signatures. Our Axion-Higgs criticality model predicts an ALP in the MeV to $\mathcal{O}(10)$ GeV range. The entire natural region of parameter space can be thoroughly explored by a combination of future colliders, flavour experiments, and cosmological observatories.

Speaker: Maximilian Detering (King's College London)

138 Amplitudes and perturbative unitarity bounds

We develop a formalism based on spinor-helicity techniques to generalize the formulation of perturbative unitarity bounds. We discuss unitarity bounds for $N \to M$ (with $N, M \geq 2$) scattering processes, relevant for high-energy future colliders, and spin-2 or higher-spin theories, relevant for effective field theories of gravity, that are not approachable by standard methods. As a byproduct of our analysis, we emphasize the power and complementarity of positivity and perturbative unitarity bounds to constrain the parameter space of effective field theories.

Speaker: Luigi Carlo Bresciani (University of Padova & INFN-PD)

19:00 Social dinner

Friday 30 May

Plenary session: Friday morning

139 A unique coupling of the massive spin-2 field to supergravity

Speaker: Emilian Dudas (Éc. Polytechnique)

140 Revisiting the gravitational two-body problem in the amplitudes framework

Speaker: Carlo Heissenberg (IPhT)

141 String Theory and the First Half of the Universe

Speaker: Joseph P. Conlon (Oxford)

142 Naturalness and Generalized Symmetries

Speaker: Seth Koren (Notre Dame)

11:00 Coffee

143 Gravitational waves from phase transitions

Speaker: Chiara Caprini (CERN)

144 Gravitational wave searches: milestones and challenges

Speaker: Valerie Domcke (CERN)

12:30 Break for lunch

Plenary session: Friday afternoon

145 Status of the muon g-2 puzzle

Speaker: Gilberto Colangelo (Bern)

146 Probing the Standard Model to 0.37 ppm with the muon anomalous magnetic moment

Speaker: Laurent Lellouch (Marseille)

147 Precision and Intensity probes of new physics

Speaker: Yotam Soreq (Technion)

148 Conclusion