String Theory Journal Club

It is well known that the Universe underwent several phase transitions during its cooling. In this talk, I will discuss the possibility that one of the cosmological transitions was a violent first-order condensation of a scalar field, which could leave fingerprints such as a detectable stochastic gravitational-wave background. The formation of these relics hinges on dynamical processes: the nucleation and expansion of true-vacuum bubbles within the supercooled medium. I will show that incorporating an effective coupling between the plasma and the scalar field fixes the entropy production, which is necessary for analytically computing the fluid profiles that form around expanding bubble walls. This effective model of background–field–plasma interactions reveals that two stable shock-wave solutions can coexist; however, real-time hydrodynamic simulations indicate that the faster solution is preferentially realized. These results will affect the phenomenological study of first-order phase transitions in a large class of Standard Model extensions.