Physics of Inverse Phase Transitions

• Giulio Barni

First-order phase transitions (FOPTs) in the early universe can generate baryogenesis, dark matter, and gravitational waves (GWs). While standard (direct) FOPTs involve plasma pushed or dragged by expanding bubbles, inverse FOPTs, where plasma is sucked into the bubble, offer a novel hydrodynamic behavior, previously thought to occur only during (re)heating. In this talk, I present the first natural realization of an inverse FOPT during cosmological cooling, arising in a SUSY-breaking model. In the O’Raifeartaigh setup, the transition along the pseudomodulus can be inverse due to the model’s thermal history. We derive a simple criterion based on a generalized pseudo-trace to distinguish inverse from direct FOPTs and show it outperforms previous estimators. These results highlight the need to incorporate inverse solutions when studying early universe dynamics and their GW signatures.