Prof. Alessandro Sarracino, The grand canonical catastrophe, revisitedHighlights

by Prof. Alessandro Sarracino (Università della Campania “Luigi Vanvitelli”)

Thursday 16 Apr 2026, 14:30 → 15:30 Europe/Rome

1/3-1 - Sala R (Dipartimento di Fisica e Astronomia - Edificio Marzolo)

The realisation of Bose-Einstein condensation under grand-canonical
conditions has provided the experimental evidence for the
simultaneous occurrence of macroscopic fluctuations and phase coherence
of the condensate. The observation of these two features, against a
consolidated tradition which wants the fluctuations to be pathological
(grand-canonical catastrophe) and incompatible with spontaneous
symmetry breaking, calls for a comprehensive rethinking of the
approach to the problem. In this talk we consider the uniform ideal
gas in a box and we present an alternative conceptual framework. We
show that the usually-employed Bogoliubov quasi-average construction
fails to reproduce the broken-symmetry state. The observed features
are accounted for by a different pattern of spontaneous symmetry
breaking, characterised by condensation of fluctuations and
long-range correlations of the order parameter.