The 23rd String Phenomenology conference is jointly organized by the Department of Physics and Astronomy "G. Galilei" of the University of Padua and the INFN  National Institute for Nuclear Physics. The event will take place at the Centro Culturale Altinate  San Gaetano of Padova, Italy.
This annual conference discusses recent progress in string theory, with a particular emphasis on aspects relevant to the theory of fundamental interactions and its phenomenological implications for particle physics and cosmology.
Plenary and parallel sessions cover the most impactful results recently presented by the community, which have unveiled new ideas and opened previously unexplored research lines. The main topics include:

Participation to this event is by registration only. The link to the registration page will become available on March 4, 2024 on the menu on the left. The registration page will include the possibility to propose a title and abstract for a parallel session talk, or a poster.
Invited Speakers


Equity, Diversity and Inclusion Talk
Marika Taylor
Scientific Committee
Michele Cicoli (University of Bologna)
Luca Martucci (University of Padua)
Raffaele Savelli (University of Rome Tor Vergata)
Roberto Valandro (University of Trieste)
Local Organizing Committee
Fabio Apruzzi (University of Padua)
Davide Cassani (INFNPadova)
Alessandra Gnecchi (INFNPadova)
Gianluca Inverso (INFNPadova)
Luca Martucci (University of Padua)
Stefano Massai (University of Padua)
Secretariat
Pina Salente (INFNPadova)
Silvana Schiavo (University of Padua)
Paola Zenere (University of Padua)
Conference Poster
Asymptotically massless towers of species are ubiquitous in the string landscape when infinitedistance limits are approached. Due to the remarkable properties of string dualities, they always comprise KaluzaKlein states or higherspin excitations of weakly coupled, asymptotically tensionless critical strings. The connection between towers of light species and small black holes warrants seeking a bottomup rationale for this dichotomoy, dubbed emergent string conjecture. We will explore bottomup constraints on towers of light species motivated purely from the consistency of the corresponding thermodynamic picture for small black holes. These constraints shed light on the allowed towers in quantum gravity providing evidence for the emergent string scenario with no reference to a specific ultraviolet completion.
We begin by studying configurations of particles at equilibrium at a temperature T inside a box in the presence of towers of species. By playing with the control parameters, we can obtain configurations that avoid gravitational collapse and fulfill the Covariant Entropy Bound (CEB). These interpolate between the usual dependence of the entropy with the volume (when T is low enough and the momentum modes available to massless particles dominate) and a dependence on the number of species that are “active” at a temperature T (when the T is high enough to “see" the towers of species). In the latter case, we recover the species entropy (and thus the area scaling of the entropy) in the limit in which the temperature approaches the maximum one, namely the species scale, which is also the point at which gravitational collapse and saturation of the CEB would occur for the smallest possible box. We then put this in the bigger picture of the black holetower correspondence, a generalization of the black holestring correspondence that allows to qualitatively account for the scaling of the entropy of black holes with their area by adiabatically following them towards weak gravitational coupling regimes, up to the point where a transition to a system whose entropy is dominated by the towers of species should occur.
We aim to derive the species thermodynamics from a bottom up perspective, namely from purely thermodynamic considerations of towers of species at finite temperature. As we will show, in a certain high temperature limit and invoking the concept of UV/IR mixing, the entropy of certain towers will change its behaviour from extensive volume scaling to an area low and in this way will end up with the same thermodynamics laws for the species particles, as obtained from the minimal black hole perspective. This will also restrict their possible mass spectra, proving another bottom up support for the emergent string conjecture.
The Festina Lente (FL) swampland bound follows from demanding that charged black holes of cosmological size in quaside Sitter space evaporate in a consistent, nonsingular way. The FL bound demands that all charged particles are heavier than a lower bound determined by the gauge coupling and vacuum energy. If one applies the FL bound to nonabelian gauge theories in de Sitter space, one finds that all nonabelian gauge theories must be either Higgsed or confined, with a characteristic scale above the Hubble scale. I will discuss an extension of these results to include finitetemperature effects. I will argue that accounting for a thermal background can significantly strengthen the constraints coming from FL. I argue that the confinement scale should be higher than a scale proportional to the vacuum energy, while Festina Lente without thermal effects only bounds the confinement scale to be above the Hubble scale. For Higgsing, I find that the magnitude of the Higgs mass should be heavier than a bound proportional the scale set by the Higgs VEV. A way to avoid the bound being violated during inflation is to have a large number of species becoming light. If one wants the inflationary scale to lie below the species scale in this case, this bounds the inflationary scale to be ≪10^5 GeV.
We propose a scenario that might result in a transient phase of cosmological acceleration on asymptotic corners of string theory moduli space. In a cosmological version of the chameleon mechanism, a steep potential is stabilized by a nonzero density of heavy states. This can also be realized by balancing effects of light and heavy towers. We show that in both cases, which end once states are diluted by the cosmological expansion, it is not possible to obtain more than O(1) efolds without transplankian values for the fields. We propose possible string embeddings and discuss the issues they might have.
I will review how black holes can be used to probe infinite distance points in moduli space and the phenomenological opportunities that lie there. Then I will discuss how the picture drastically changes when one considers a vacuum where the scalars are stabilized.
The standard reheating process after inflation can be anticipated by a phase of preheating, where the oscillations of the inflaton field at the bottom of its potential give rise to an explosive production of particles via parametric resonance, which can potentially alter the history of the universe. In this talk, I consider an inflating modulus coupled to an axion via a typical potential coming from type IIB string theory on CalabiYau orientifolds. First, I will show that parametric resonance in string inflation has distinctive outcomes which depart from the usual EFT results. Then, I will study specific models and show how the production of axions via parametric resonance imposes interesting constraints to model building.
Metastable de Sitter vacua are widely explored in the classical corner of string theory and notoriously difficult to realise. In addition, metastable de Sitter vacua in the parametrically controlled region have been conjectured to be in the Swampland. In this talk we explore a nonsupersymmetric corner of string theory given by type II ScherkSchwarz toroidal orbifolds, where supersymmetry is broken at the compactification scale and the 1loop vacuum energy can be computed. We provide nogo theorems for (quantum) de Sitter solutions in d=8,9. We also show that any de Sitter solution in d=4 or bigger is unavoidably perturbatively unstable. Finally, we comment on the difficulty of realising such de Sitter solutions in the weakly coupled/large volume regime as in accordance with de Sitter Swampland conjectures. In contrast, AdS solutions under parametric control can be easily realised.
Scaleseparated AdS compactifications of string theory can be constructed at the twoderivative supergravity level in the presence of smeared orientifold planes. The "unsmearing" corrections are known to leading order in the large volume, weak coupling limit. However, firstorder perturbative approximations of nonlinear problems can often produce spurious solutions, which are only weeded out by additional consistency conditions imposed by higherorder terms. In this talk, we revisit the "unsmearing" procedure and present consistency conditions obtained at second order, which can be written as integral constraints on various nonlinear combinations of the first order corrections. We will then describe when and how these constraints can be satisfied and discuss the implications for the consistency of scaleseparated AdS compactifications.
For the antiD3brane uplift one places $p$ antiD3branes at the tip of a KlebanovStrassler (KS) throat. This setup can only contribute positively to the vacuum energy if it is stable against the so called KPV decay where the antibranes puff up into an NS5brane which subsequently annihilates against flux and forms a supersymmetric state at zero vacuum energy. In this talk, I will discuss this setup of $p$ antiD3 branes at the tip of the KS throat at higher orders in $\alpha'$ from the perspective of a nonabelian stack of D3branes and recap some earlier results from the puffed up NS5brane perspective. I will point out advantages of both pictures and discuss implications for phenomenology.
We study structures of solutions for SUSY Minkowski Fterm equations on two toroidal orientifolds with h2,1=1. Following our previous study (2011.09154), with fixed upper bounds of a flux D3brane charge Nflux, we obtain a whole Landscape and a distribution of degeneracies of physicallydistinct solutions for each case. In contrast to our previous study, we consider a nonfactorizable toroidal orientifold and its Landscape on which SL(2,ℤ) is violated into a certain congruence subgroup, as it had been known in past studies. We find that it is not the entire duality group that a complexstructure modulus U enjoys but its outer semidirect product with a "scaling" outer automorphism group. The fundamental region is enlarged to include the U<1 region. In addition, we find that high degeneracy is observed at an elliptic point, not of SL(2,Z) but of the outer automorphism group. Furthermore, ℤ2enhanced symmetry is realized on the elliptic point. The outer automorphism group is exceptional in the sense that it is consistent with a symplectic basis transformation of background threecycles, as opposed to the outer automorphism group of SL(2,ℤ). We also compare this result with Landscape of another factorizable toroidal orientifold. This work is based on arXiv:2311.12425 [hepth].
Three distinct infinite distance limits appear in the conformal manifolds of fourdimensional superconformal field theories admitting large N limit. They are distinguished by the CFT Distance Conjecture parameter, controlling the exponential behavior with the distance of the anomalous dimension of higherspin currents. Borrowing lessons from the moduli spaces of flat space vacua in string theory, we argue that these three limits correspond to three different strings becoming tensionless in AdS. To support this claim, we show that the large N Hagedorn temperature of the CFT in these limits only depends on the CFT Distance Conjecture parameter. Thus, these three limits are physically distinguished by the density of states at high energies. Along the way, we build the first Distance Conjecture convex hull for a CFT and find a remarkable connection to no separation of scales in AdS.
I will discuss the computation of correlators and observable quantities, in particular OPE coefficients, in ArgyresDouglas theories, that are 4dimensional N = 2 superconformal field theories, intrinsically strongly coupled and without a Lagrangian description. I will recall some results for extremal correlators and OPE coefficients derived through localization on the 4sphere, showing their almost compatibility with the conformal boostrap method. Then I will pass to discuss the large Rcharge limit for the localization results, in order to compare them with the ones obtained through the EFT technique, and in this scenario I will present some new coefficients coming inside the perturbative expansion, showing also consistency with what already known in literature. Finally, I will show some results about the goodness of a particular ansatz that produces a match with the results from the EFT method much better.
New methods have emerged in the context of black hole perturbation theory, which are based on the correspondence between the equations describing the propagation of waves in these geometries and the SeibergWitten curves for an N=2 SYM theory with SU(2) gauge group in the noncommutative NekrasovShatashvili background. These techniques are employed to compute observables such as quasinormal modes, tidal deformations, and amplification factors, aiming to distinguish black holes from other compact geometries.
We investigate the highenergy fixedangle scattering of pions and rho mesons in a holographic QCD model, following the PolchinskiStrassler proposal. In agreement with earlier findings of Polchinski, Strassler and other authors, we observe partonic behaviour coming from string amplitudes in AdS spacetime. In our holographic approach, 2ton pion scattering amplitudes display agreement with known constituent counting rules found in QCD and other asymptotically free confining gauge theories. However, in naïve disagreement with these rules, we further report that 2ton scattering amplitudes that involve rho mesons, and where all the other scattered states can be pions, are suppressed in Mandelstams relative to the 2ton pion scattering amplitudes. Finally, several plots of differential crosssections for 2to2 pion scattering as a function of s and the scattering angle are obtained at fixed values of s and separately at fixed scattering angles, some of the predictions are compared to experimental data and phenomenological aspects are discussed.
Utilizing freely acting asymmetric orbifolds in type IIB string theory, we construct a class of theories in 5D and 4D with 8 supercharges, where the moduli spaces for both vector multiplets and hypermultiplets can be determined without quantum corrections. By tuning the duality twist, all fields from the RR sector can be rendered massive. This talk highlights two minimal examples: one with only two moduli in 5 dimensions, and another with only three moduli in 4 dimensions. All examples receive no perturbative nor nonperturbative corrections.
We present a new technique to derive the quiver and the superpotential of a D2brane probe at the singularity of a specific class of CalabiYau Threefolds. These spaces are constructed as non trivial fibrations of deformed ADE singularities on a complex plane and can be conceived as non toric generalizations of the conifold geometry. We establish a correspondence between monopole operator deformations of the 3d superpotential and resolution patterns of the probed geometry.
Dynamical Cobordism is an implementation of the Cobordism Conjecture in the framework of Effective Field Theory, with EndoftheWorld (ETW) Branes realized as codimension1 solutions of the EFT becoming singular at infinite field distance and finite spacetime distance. In this talk, I will describe how codimension2 ETW branes can be realized as intersecting solutions, providing both a general framework and specific examples for this description. From the cobordism perspective, the intersections can be regarded as describing the end of the world for endoftheworld branes, or as boundary domain walls interpolating between different ETW brane boundary conditions for the same bulk theory.
In the presence of massless scalar fields, mediating longrange forces, the Weak Gravity Conjecture (WGC) must be modified to take such interactions into account. This suggested the possibility that a relation analogous to the WGC could hold for scalar fields only, dubbed Scalar Weak Gravity Conjecture (SWGC). In this talk we discuss the SWGC in the case where the scalar fields are compactification moduli, a setup which allows to probe the conjecture and test its validity. More specifically, we'll discuss under which conditions the SWGC can be satisfied, its relation to the WGC, its stability under dimensional reduction and its potential connection with identities in supergravity.
In six dimensions, there is an exotic N=(4,0) supermultiplet that contains only fields of spin ≤2, but no graviton, and that on a circle reduces to 5D N=4 supergravity. It has been proposed that, if suitable interactions exist, the (4,0) theory might provide a consistent alternative UV completion for N=4 5D supergravity, realizing a supersymmetric version of asymptotic safety. We argue that any Lorentzinvariant (4,0) theory (interacting or not) carries an exact global symmetry when compactified on S1, and is therefore incompatible with the Swampland no global symmetries conjecture. Another example of exotic supergravity, the 6D (3,1) theory, does not have this problem. We study the general case and find that the only exotic spin2 field that reduces to Einsteinian gravity and has no global symmetries when compactified on a highdimensional torus is that of the (3,1) theory. All other possibilities either yield several gravitons or have global symmetries.
The cobordism conjecture predicts endoftheworld (ETW) branes to generally exist. As a consequence, universes can decay to nothing and be created from nothing in various ways. We discuss how the existence of ETW branes changes predictions cosmological predictions.
Cobordism offers an unique perspective into the nonperturbative sector of string theory by demanding quantum gravitational consistency.
The dynamical realization of the cobordism conjecture in type IIB in AdS5xS5 will be presented, using the existing gravity duals of 4d N = 4 SYM with GaiottoWitten superconformal boundary conditions (nearhorizon limits of D3branes ending on NS5 and D5branes). These configurations are, from the 5d perspective, dynamical cobordism solutions which start from an asymptotic AdS5 vacuum and evolve until they hit an end of the world (ETW) brane with AdS4 worldvolume. The latter displays localization of gravity, and provides a completion of the KarchRandall (KR) AdS branes, in which the backreaction of running scalars replace the KR cusp in the warp factor with a smooth bump.
First, we generalize the construction of scaleseparated vacua in massless Type IIA compactified on an SU(3)structure manifold with geometric fluxes beyond the double Tdualization of a DGKT toroidal orbifold. We propose new infinite families of vacua based on elliptic fibrations with metric fluxes. They display parametric scale separation, achieved by an asymmetric flux rescaling.
Controlled de Sitter vacua, if they exist, seem to be hiding in difficult regions of the string Landscape  they seem to require such an intricate interplay of ingredients, that many things can go wrong and invalidate the solutions. In fact, checking their validity with explicit computations is itself a difficult task. With this in mind, we explore a combination of ingredients that are both common and simple enough to be computed explicitly  flat manifolds, fluxes and Casimir energies  and could in principle provide de Sitter vacua in 3d and 4d.
In our research, we studied the decay of the KaluzaKlein vacuum via an instanton solution, which has a singularity. For the KaluzaKlein vacuum, there is a nonperturbative decay channel where literally a "bubble of nothing" expands and overwhelms the spacetime. The instanton solution that mediates this decay is the Euclidean 5D Schwarzshild solution, and, in general discussion, we fix the periodicity of the imaginary time to an appropriate value to avoid a singularity at the location of the event horizon. We relax this smoothness condition and evaluate the contribution of the singularity based on the conical deficit regularization. This contribution is always negative and finite and works to reduce the Euclidean action. If this argument is correct, decay via singular instantons may be a more dominant process in higherdimensional theories. Moreover, we also reproduce the bounce action using thermodynamic functions and attempt a thermodynamic interpretation of the aforementioned catalytic effects.
Highercurvature corrections appear naturally as stringy corrections in the different effective actions of String Theory. In recent years this has motivated an intensive research on highercurvature terms by themselves, beyond their fundamental origin. In this contribution, I will focus first on showing how a very special class of highercurvature theories may be used to study \alpha’ corrections in String Theory, illustrating this feature with an explicit example. Secondly, I will present how the Weak Gravity Conjecture may be used to constrain lowenergy effective actions which are consistent with Quantum Gravity.
The AdS Distance conjecture proposes a notion of distance between AdS vacua in quantum gravity. Although the need for such a notion is evident, defining and computing this distance is challenging, both conceptually and technically. In my talk, I will address this challenge by proposing a consistent framework for defining and computing the metric over AdS vacua, establishing a welldefined distance. The key idea involves considering the offshell quadratic variation of the string theory action and evaluating it over the space of onshell solutions. I will particularly focus on DGKT vacua. Given the ongoing debate regarding whether these vacua exist as fully localized solutions, it is particularly intriguing to test our proposed metric over AdS vacua within this framework. I will show that DGKT vacua exhibit a positive metric, yielding a welldefined AdS distance. In conclusion, I will introduce a potential new Swampland criterion, suggesting that the metric over the space of vacua in quantum gravity, as defined by our proposed procedure, is positive definite.
Talk from the paper https://arxiv.org/pdf/2405.01084 in collaboration with Eran Palti (BenGurion U.)
Flux compactifications that give three or fourdimensional AntideSitter vacua with a parametricallysmall negative cosmological constant are supposed to be ubiquitous in String Theory. However, the 1+1 and 2+1 dimensional CFT duals to such vacua should have a very large central charges and rather unusual spectra. Furthermore, there are various swampland conjectures that such vacua should not exist. In this talk, I will explain how we construct brane configurations that source the wouldbe AdS vacua coming out of these flux compactifications, and identify certain UV AdS geometries that these systems of branes source. These place upper bounds on the possible values of the cosmological constants of the scaleseparated AdS vacua.
In the past four decades of string theory research, the O(16) × O(16) heterotic string in 10d has
stood alone as the only nonsupersymmetric, tachyonfree string model with one scalar. We introduce new nonsupersymmetric and tachyonfree string theories that serve as the lowerdimensional
counterparts to the O(16) × O(16) string in 4d, 6d, and 8d, each featuring only one neutral scalar.
The lack of experimental evidence for supersymmetry has recently fueled a resurgence of interest in nonsupersymmetric strings, where supersymmetry is absent at the string scale. In particular, new theories have been found recently with a very rich and interesting spectra.
A great deal of effort has been put in understanding the structure underlying the supersymmetric landscape. Much of it is retained for some classes of nonsupersymmetric theories, allowing for a precise description of their moduli spaces, predicting new ones, finding dualities between them and relating their spectra with their supersymmetric counterparts.
Moreover, an analysis of geodesics and their infinite distance limits reveals a complex web interrelating both known and previously unknown theories, while the asymptotic behavior of the states becoming massless suggests that some constraints imposed by the swampland program seem to hold when going out of the supersymmetric lamppost.
The landscape of lowenergy effective field theories stemming from string theory is too vast for a systematic exploration. However, the meadows of the string landscape may be fertile ground for the application of machine learning techniques. In this talk, I will illustrate that Quantum Gravity effective field theories are endowed with key statistical learnability properties due to their underlying tame structures. Consequently, several problems therein formulated can be concretely addressed with machine learning techniques, delivering results with sufficiently high accuracy.
The gravitational backreaction of the absence of spacetime supersymmetry in string theory has dramatic effects, forbidding the treelevel flat Minkowski and requiring new vacuum solutions. A similar fate is expected for localized sources: brane solutions must change drastically.
In this talk, I will discuss ongoing work on the gravity description of branes in nonsupersymmetric tachyonfree tendimensional strings, emphasizing the emergence of universal asymptotic behavior.
I will also describe an alternative viewpoint in which branes are embedded in the shifted vacuum.
Brane Supersymmetry Breaking (BSB) is a phenomenon occurring in lower dimensional orientifold vacua in which supersymmetry is broken without admitting tachyonic instabilities. Such vacua are characterised by the simultaneous presence of a treelevel supersymmetric closed string sector coupled with a nonsupersymmetric open string one, which underlies a nonlinear realisation of supersymmetry. After reviewing the original construction in six dimensions built on the T^4/Z_2 orbifold, I will present an almost rigid variation that can only be deformed via an overall Dbranes recombination. Afterwards, I will describe the BSB orientifold built upon the T^4/Z_4 orbifold in which, in contrast to the previous case, the presence of fractional orientifold planes forbids any further continuous deformation. Finally, I will briefly comment on the structure of the gauge kinetic functions entering the lowenergy effective action and the unitarity constraints arising from the presence of 2d defects coupled to the RR 2forms required by the GreenSchwarzSagnotti mechanism.
We revisit the GreenSchwarz (GS) mechanism in the 10d Sugimoto model and explicitly show the consistency with anomalyinflow onto the branes involved in the GSmechanism. The branes’ degrees of freedom establishes Sp(16) as the global gauge group of the 10d nonsupersymmetric theory. We then interpret and generalize the computation with a bottomup perspective, to study the consistency of nonsupersymmetric sp(16) gauge theories with different chiral spectra coupled to gravity. Our findings suggest that it is surprisingly challenging to have a consistent theory with Sp(16)/Z2 gauge group.
Does string theory predict extra dimensions? It is common folklore that consistency dictates ten or eleven in total. However, the structures appearing in string theory generalize the classical notion of geometry to something more abstract, which may not always reduce to the familiar idea of compact extra dimensions. I will present some recent results to the effect that classical geometry does emerge toward the boundary of moduli space in perturbative string vacua.
In its original formulation, the Emergence Proposal postulates that terms in the lowenergy effective action are emerging by integrating out towers of states becoming exponentially light in asymptotic regions of the moduli space, in agreement with the Swampland Distance Conjecture. In this talk, I will motivate an Mtheoretic refinement of the Emergence Proposal by revisiting the computation of a particular higher derivative coupling in toroidal compactifications of Mtheory. On a technical level, these calculations rely on employing an appropriate regularization method and demonstrate that integrating out the full infinite towers of light states is crucial for reproducing the known results completely.
We study limits of vanishing Yukawa couplings in Quantum Gravity, using type IIA orientifolds as a laboratory. We show that in the limit Y → 0 there are some towers (called gonions) which become asymptotically massless, while at the same time, the kinetic term of some chiral fields becomes singular. In addition, we study how tiny masses of Dirac neutrinos can arise consistent with experimental constraints on SMtype vacua in string theory. We find that two large hidden dimensions arise only perceived by the ν_R sector, while the string scale is around Ms≃gνMP≃10700 TeV. As a byproduct, independently of the neutrino issue, we argue that a single large dimension in the context of SMlike type IIA CalabiYau orientifolds leads to too small Yukawa couplings for quarks and charged leptons.
In the context of the Swampland program, the Distance Conjecture predicts an infinite tower of states becoming massless at infinite distance in moduli spaces of string compactifications. This is widely believed to be a general feature of quantum gravity, but it is difficult to prove in full generality. On the other hand, the moduli spaces of maximally and halfmaximally supersymmetric theory are coset spaces of the globally symmetric type, which are mathematically fairly well understood. In this work, we provide a framework to study systematically the infinite distance limits in these simple cases, and use this knowledge to argue for the Distance Conjecture in this subset of theories.
We use branes to generalize the Distance Conjecture. We conjecture that, in any asymptotic distance phi in the moduli space of string vacua of a ddimensional theory, among the set of particle towers or branes with at most p spacetime dimensions, at least one particle tower or brane becomes exponentially low tension by the formula T~exp(alpha phi) where alpha is at least 1/sqrt(dp1). Since p can vary, this is multiple conjectures in one, and the Sharpened Distance Conjecture is the p=1 case. This conjecture is a necessary condition imposed on higherdimensional theories in order for the Sharpened Distance Conjecture to hold in lowerdimensional theories. We test this proposal in multiple 32 and 16 supercharge examples in diverse dimensions, and see that our conjecture is satisfied and often saturated.
(Based on work with Ben Heidenreich and Tom Rudelius).
Dynamical Cobordism provides a powerful method to probe infinite distance limits in moduli/field spaces parameterized by scalars constrained by generic potentials, employing configurations of codimension1 end of the world (ETW) branes. These branes, characterized in terms of critical exponents, mark codimension1 boundaries in the spacetime in correspondence of finite spacetime distance singularities at which the scalars diverge. Using these tools, I will explore the network of infinite distance singularities in the complex structure moduli space of CalabiYau fourfolds compactifications in Mtheory with a fourform flux turned on, which is described in terms of normal intersecting divisors classified by asymptotic Hodge theory. I will provide spacetime realizations for these loci in terms of networks of intersecting codimension1 ETW branes classified by specific critical exponents which encapsulate the relevant information of the asymptotic Hodge structure characterizing the corresponding divisors.
We perform a detailed study of stringy modulidriven cosmologies between the end of inflation and the commencement of the Hot Big Bang, including both the background and cosmological perturbations: a period that can cover half the lifetime of the universe on a logarithmic scale. Compared to the standard cosmology, stringy cosmologies motivate extended kination, tracker and modulidominated epochs involving significantly transPlanckian field excursions. Conventional effective field theory is unable to control Plancksuppressed operators and so such epochs require a stringy completion for a consistent analysis. Perturbation growth in these stringy cosmologies is substantially enhanced compared to conventional cosmological histories. The transPlanckian field evolution results in radical changes to Standard Model couplings during this history and we outline potential applications to baryogenesis, dark matter and gravitational wave production.
I will discuss stringy, modulidriven cosmologies between the end of inflation and the commencement of the Hot Big Bang,a period that can cover half the lifetime of the universe on a logarithmic scale. Compared to the standard cosmology, stringy cosmologies motivate extended kination, tracker and modulidominated epochs involving significantly transPlanckian field excursions. The transPlanckian field evolution may result in radical changes to Standard Model couplings during this history, such as a timedependent string scale. We will highlight how this can naturally explain a population of cosmic superstrings compatible with existing bounds, and provide predictions for their gravitational wave signatures.
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. However, string axions do not necessarily need to couple to the Standard Model directly. In this talk I will describe how inflationary models with multiple “spectator" axions coupled dark gauge sectors via ChernSimons coupling could source observable gravitational waves.
If string axions coupled to Abelian gauge fields undergo slowroll during inflation, they produce a multipeak GW signal whose magnitude depends on the details of the compactification. I will discuss how to embed spectator axions into type IIB orientifold compactifications and the restrictions imposed on such models from consistency and control requirements, thereby motivating models that may live in the landscape as opposed to the swampland.
The topic of this talk will be a new inflationary model called ‘Loop BlowUp Inflation’, first presented in 2403.04831. This model is based on string loop corrections to the scalar potential of ‘Kähler moduli inflation’, which originally featured only nonperturbative contributions. The perturbative effects become dominant over the nonperturbative ones as soon as the inflaton is displaced from its postinflationary minimum. This gives rise to a new form of inflationary potential with an inversepower law behaviour. Slowroll inflation can happen with control over the effective theory. This talk will focus mostly on the postinflationary history predicted for different brane setups that realize the Standard Model. The predictions for the spectral index, the tensortoscalar ratio, and dark radiation are in good agreement with CMB data.
We study in detail and generalise a recent formulation of braneantibrane inflation in which the problems of the original formulations are addressed: separation between branes larger than the size of the extra dimension, lack of modulus stabilisation, the eta problem, and the reduction of the setup to the unrealistic inflection point inflation. We explicitly compute the effect of brane antibrane attraction in a supersymmetric way in terms of general nilpotent superfield interactions and include perturbative moduli stabilisation. We determine the region of parameter space in which realistic slowroll inflation is allowed as well as latetime modulus stabilisation with the volume hierarchically larger than its value during inflation. The inflationary region corresponds to the standard Coulomb attraction potential with a realistic value of the spectral index and a very small tensortoscalar ratio. The parameter space determined by imposing a series of consistency conditions to have control on the approximations and experimental constraints is large enough indicating that inflation happens naturally in this scenario.
Using flat space string amplitudes and recently computed equilibration rates for a gas of highly excited strings, we argue that a Hagedorn phase could have occured in the early Universe with a bath of open strings dominating the energy density. These strings would predominantly decay in Standard Model fields, providing a successful reheating, and would release a gravitational wave spectrum whose amplitude peaks at a frequency similar to the Cosmic Gravitational Wave Background predicted by the Standard Model, but with a generically larger amplitude, which depends linearly with the local string scale.
We study the phenomenological usefulness of including geometric and nongeometric fluxes to the fluxinduced scalar potential for type IIA orientifolds. The resulting potential presents a bilinear structure, which we use to explore two topics: scale separation and the search of dS vacua. First, we generalize the construction of scaleseparated vacua in massless Type IIA compactified on an SU(3)structure manifold with geometric fluxes. We propose new infinite families of vacua based on elliptic fibrations with metric fluxes. They display parametric scale separation, achieved by an asymmetric flux rescaling. Second, we perform an analytical exploration of de Sitter conditions in type IIA compactifications with (non)geometric fluxes. We find four conditions that the scalar fields and fluxes must satisfy to achieve dS vacua, extending previous results in the literature. We then impose an Ansatz in which the Fterms are proportional to the respective Kähler derivatives. In this setup we are able to derive additional constraints and to classify the possible dS nogo scenarios.
6d supergravity with minimal supersymmetry is highly constrained by various lowenergy consistency conditions, including anomaly cancellation. In this talk I will discuss the use of ideas from graph theory to exhaustively enumerate all consistent models with few tensor multiplets (modulo some minimal assumptions). Testing this complete list of models against several Swampland bounds reduces their number by ~50%.
Based on 2401.00549
The dualization of the scalar fields of a theory into (d2)form potentials preserving all the global symmetries is one of the main problems in the construction of democratic pseudoactions containing simultaneously all the original fields and their duals. We study this problem starting with the simplest cases and we show how it can be solved for scalars parametrizing Riemannian symmetric sigmamodels as in maximal and halfmaximal supergravities. Then, we use this result to write democratic pseudoactions for theories in which the scalars are nonminimally coupled to (p+1)form potentials in any dimension. These results include a proposal of democratic pseudoaction for the generic bosonic sector of 4dimensional maximal and halfmaximal ungauged supergravities. Furthermore, we propose a democratic pseudoaction for the bosonic sector of N=2B,d=10 supergravity (the effective action of the type IIB superstring theory) containing two 0, two 2, one 4, two 6 and three 8forms which is manifestly invariant under global SL(2,R) transformations.
A classification proposal exists for string vacua with 16 supercharges in six dimensions. It predicts in particular a family of type II strings without moduli apart from the dilaton, including the only known example given by Dabholkar and Harvey some time ago. It is also predicted that some of these theories admit nontrivial discrete theta angles. Here I will show how such theories can be constructed as asymmetric orbifolds.
I will discuss supersymmetric AdS_3 flux vacua of massive type IIA supergravity on G2 orientifolds, focusing on (non) scale separated configurations at large volume and weak coupling, even highly anisotropic. I will also present the realization of the Swampland Distance Conjecture within such setups via the inclusion of appropriate D4branes.
In addition, inspired by the desire of finding all possible flux choices which give rise to the aforementioned AdS_3 scaleseparated configurations, I will discuss some recent developments concerning a systematic study of Mtheory and typeII flux vacua in three dimensions, including gauge and metric fluxes, Oplanes and Dbranes, and admitting a description in terms of threedimensional gauged supergravitites with halfmaximal supersymmetry.
Scale separation is the important phenomenological property for a given vacuum to have an internal compact space much "smaller" than the extended spacetime, so that a lowerdimensional effective description indeed makes sense. At a practical level, this is measured by the decoupling or not of the magnitude of the cosmological constant from the KaluzaKlein scale. The status of scale separation in AdS vacua obtained from string theory is under debate. On the one hand bottomup constructions in type IIA string theory seem to achieve this hierarchy of scales parametrically. However on the other hand some Swampland arguments as well as holographic considerations cast a pessimistic shadow on scale separation and about its presence in the Landscape. After a brief overview of the evolution of scale separation in string theory over the last twenty years, I will present new families of scale separated vacua obtained via a 4d EFT analysis in massless type IIA flux compactifications on elliptic fibrations with metric fluxes. Parametric scale separation is achieved by an asymmetric flux rescaling which, however, in general is not a simple symmetry of the 4d equations of motion. At this level of approximation the vacua are stable but, unlike in the CalabiYau case, they display a nonuniversal mass spectrum of light fields.
We examine the minimal constraints imposed by the Weak Gravity Conjecture (WGC) on the particle spectrum of quantum gravity theories. Recently, we argued for the existence of a minimal radius in circle reductions of generic quantum gravity theories. Consequently, whenever a minimal radius exists and the WGC is satisfied at the particle level below the black hole threshold by some states, these states are sufficient for consistency under dimensional reduction, even without a tower of superextremal particles. Conversely, the absence of a minimal radius always coincides with the presence of a weakly coupled superextremal tower of particle states. This observation motivates the Minimal Weak Gravity Conjecture, which posits that towers of superextremal particles appear only when required for consistency of the WGC under dimensional reduction. The talk is based on [2312.04619].
In its original version, the Emergence Proposal states that the kinetic terms of all fields in the lowenergy effective action arise from integrating out towers of states becoming light in asymptotic corners of the moduli space. In my talk I want to motivate why the natural home of the Emergence Proposal should be Mtheory. I will discuss this idea in the context of a wellknown setup, namely the vector multiplet moduli space of type IIA N=2 vacua in four dimensions. For the Mtheory limit, one can setup an emergence computation for certain topological quantities thanks to the seminal work of Gopakumar and Vafa. I will demonstrate the computation of the genusone free energy for the (noncompact) resolved conifold.
In this work, we explore the realization of the Convex Hull version of the Swampland Distance Conjecture in various 4D N=1 effective theories. In these setups, we identify the infinite towers of states that become light in the infinite distance limits and we compute the corresponding scalar chargetomass ratio vectors in order to construct their convex hull. We consider the possible EFT string limits and their associated chargetomass vectors and explore their relation with the convex hull of light towers.
We analyse the scalar curvature of the vector multiplet moduli space of type IIA string theory compactified on a Calabi–Yau manifold. While the volume of this moduli space is known to be finite, cases have been found where the scalar curvature diverges positively along trajectories of infinite distance. We classify the asymptotic behaviour of the scalar curvature for all large volume limits within the moduli space, for any choice of CalabiYau, and provide the source of the divergence both in geometric and physical terms. Geometrically, there are effective divisors whose volumes do not vary along the limit. Physically, the EFT subsector associated to such divisors is decoupled from gravity along the limit, and defines a rigid N = 2 field theory with a nonvanishing moduli space curvature. We propose that the relation between scalar curvature divergences and field theories decoupled from gravity is a common trait of moduli spaces compatible with quantum gravity.
We present some recent progress about the study of the moduli space curvature along infinite distance limits. We consider the vector multiplet sector of type IIA string theory compactified on a CalabiYau threefold, where such limits can be roughly classified as Mtheory limits, Ftheory limits or emergent string limits. We discuss the relation between divergences of the scalar curvature, that arise both at the classical level and including quantum corrections, and properties of gauge theory sectors that decouple from gravity. In particular, we focus our attention on the imprint of LSTs and SCFTs on the moduli space curvature.
The distance conjecture diagnoses viable lowenergy effective realisations of consistent theories of quantum gravity by examining
their breakdown at infinite distance in their parameter space. At the
same time, infinite distance points in parameter space are naturally intertwined with string dualities. We explore the implications of the distance conjecture when Tduality is applied to curved compact manifolds and in presence of (non)geometric fluxes. We provide evidence of how divergent potentials signal pathological infinite distance points in the scalar field space where towers of light states cannot be sustained by the curved background. This leads us to suggest an extension to the current statement of the Swampland distance conjecture in curved spaces or in presence of nontrivial fluxes supporting the background.
We investigate the dynamics of a multifield dark energy model, which arises from certain rapidturning and inspiraling trajectories in field space. We find the speed of sound of the dark energy perturbations around the background and show that this speed is monotonically decreasing with time. Furthermore, it has a positivedefinite lower bound that implies a certain clustering scale. We also extend the previously known background solution for dark energy to an exact solution that includes matter. This allows us to address the implications of our model for the Hubble and $\sigma_8$ tensions. The latter are important observational puzzles that motivate the study of cosmological models beyond $\Lambda$ CDM.
It is known that singlefield models of accelerated expansion with nearly flat potentials, despite being able to provide observationally viable explanations for the earlytime cosmic inflation and the latetime cosmic acceleration, are in strong tension with the conjectured de Sitter swampland constraints. It has recently been argued that in an open universe, where the spatial curvature is negative (i.e., with $\Omega_K>0$), a new stable fixed point arises, which may lead to viable singlefieldbased accelerated expansion with an arbitrarily steep potential. In this talk, I will show, through a dynamical systems analysis and a Bayesian statistical inference of cosmological parameters, that the additional cosmological solutions based on the new fixed point do not render steeppotential, singlefield, accelerated expansion observationally viable. I will mainly focus on quintessence models of dark energy, but I will also argue that a similar conclusion can be drawn for cosmic inflation.
Any scalar FLRWcosmology with multifield multiexponential potentials exhibits a universal bound on latetime cosmic acceleration. We discuss the conditions under which scaling solutions are inevitable latetime attractors for this class of theories. Without the need to find explicit solutions to the cosmological equations, we are also able to identify bounds on the latetime expansion rate of the universe in the additional presence of fluids with constant equation of state and of scalars with exponential kinetic couplings. We can further see how the contraction rate of cosmologies with negative potentials can be bounded by similar methods as those for cosmic acceleration.
In this talk, I discuss how a charged Nariai black hole arises in the dark bubble scenario, as a brane embedding in an AdS5 black string background. The construction allows us to identify the U(1) gauge coupling, arising from the D3worldvolume gauge theory, in terms of the string coupling and gives the same relation as was found previously for microscopic black holes.
This presentation delves into recent developments in string cosmology, specifically focusing on the refinement of the HohmZwiebach approach through an Hamiltonian reformulation. A general criterion is established to have $\mathcal{O}(d,d)$
invariant actions to all orders in $\alpha'$
connecting
$T$duality related perturbative solutions of string cosmology equations. Assuming a timely approach to the perturbative string vacuum with zero curvature and string coupling, our solutions demonstrate dilaton stabilization at later times. The result converges dynamically towards a matterdominated FLRW cosmology or a DeSitterlike inflationary phase, dependent on the initial conditions and the characteristics of the dilation potential. As a remarkable feature, for the same class of initial conditions, this scenario also provides a mechanism to wash out (arbitrarly large) anisotropic initial conditions.
This work explores Hamiltonian reformulations, nonperturbative effects, and the emergence of late time attractors in string cosmology.
The presentation will be based on arXiv:2308.16076
We analyse theories that do not have a de Sitter vacuum and cannot lead to slowroll quintessence, but which nevertheless support a transient era of accelerated cosmological expansion due to interactions between a scalar and either a hidden sector thermal bath, which evolves as Dark Radiation, or an extremelylight component of Dark Matter. We show that simple models can explain the presentday Dark Energy of the Universe consistently with current observations. This is possible both when the scalar's potential has a hilltop form and when it has a steep exponential runaway, as might naturally arise from string theory. We also discuss a related theory of multifield quintessence, in which the scalar is coupled to a sector that sources a subdominant component of Dark Energy, which overcomes many of the challenges of slowroll quintessence.
The landscape of TypeII Little String Theories (LSTs) is very sparse compared to its Heterotic counterpart. We show that this difference can be explained by analysing the bounds imposed on their flavor symmetries when demanding unitarity of the worldsheet theory. We then study TypeII LSTs from the bottom up through the associated Superconformal Field Theories, enabling us to identify Tdual pairs via certain dualityinvariant quantities. Finally, we confirm the duality explicitely by giving a topdown geometric construction via Ftheory.
FTheoryTools (https://docs.oscarsystem.org/stable/Experimental/FTheoryTools/introduction/) is an indevelopment component of the OSCAR computer algebra system (https://www.oscarsystem.org/).
The goal is to automate tedious computations in the field of Ftheory.
Among others, a large database of existing models from the literature is included (in compliance with the established MARDI standard: https://www.mardi4nfdi.de/about/mission). Thereby, complicated geometries underlying constructions from the literature can be created with the click of a button.
Recall also that nontrivial Ftheory vacua are defined by singular geometries, which are currently best understood by crepantly resolving the singularities. Among its many features, FTheoryTools allows executing such resolutions.
I will provide an overview of FTheoryTools and how it can be used to facilitate and simplify future Ftheory research.
Higgsing on symmetric matter in an SU(N) gauge theory breaks to a special SO(N) subgroup with exotic matter representations. We discuss the explicit realization of such Higgsings in Ftheory models and analyze the resulting models via dualities with heterotic and type IIB. The SO(N) gauge factors are supported on Kodaira type I_N singularities with nontrivial Tate monodromy. These models have nontrivial global gauge group quotients with no apparent Mordell–Weil torsion or additional U(1) factors, and our results suggest that one can similarly obtain a locally supported U(1) gauge factor without additional Mordell–Weil sections.
We present a numerical computation, based on neural network techniques, of the physical Yukawa couplings in a heterotic string theory model obtained by compactifying on a smooth CalabiYau threefold. We consider one of a large class of heterotic line bundle models which give precisely the MSSM lowenergy spectrum plus fields uncharged under the standardmodel group. The relevant quantities, that is, the Ricciflat CalabiYau metric, the Hermitian YangMills bundle metrics and the harmonic bundlevalued forms, are all computed by training suitable neural networks. The calculation is carried out at several points along a oneparameter family in complex structure moduli space, and each complete calculation takes about half a day on a laptop. The methods presented here generalise to other string models and constructions, including to Ftheory models.
Vector bundles made from sums of line bundles have proven to be a particularly fruitful region of the heterotic string landscape, with tens of thousands of models having the exact particle spectrum of the MSSM. A salient feature of these models is their unique and highly constraining S(U(1)^N) flavour symmetry, which strongly affects lowenergy physics. In this talk, we apply genetic algorithms to explore the flavour symmetries of these models, focussing on the quark sector of the MSSM.
One of the challenges of heterotic compactification on a CalabiYau threefold is to determine the physical (27)3 Yukawa couplings of the resulting fourdimensional N=1 theory. In general, the calculation necessitates knowledge of the Ricciflat metric. However, in the standard embedding, which references the tangent bundle, we can compute normalized Yukawa couplings from the WeilPetersson metric on the moduli space of complex structure deformations of the CalabiYau manifold. In various examples (the Fermat quintic, the intersection of two cubics in ℙ5, and the TianYau manifold), we calculate the normalized Yukawa couplings for (2,1)forms using the WeilPetersson metric obtained from the KodairaSpencer map. In cases where h1,1=1, this is compared to a complementary calculation based on performing period integrals. A third expression for the normalized Yukawa couplings is obtained from a machine learned approximate Ricciflat metric making use of explicit harmonic representatives. The excellent agreement between the different approaches opens the door to precision string phenomenology.