Rudin Petrossian-Byrne (ICTP, Trieste), Reflections on Bubble Walls


Cosmological phase transitions that proceed via nucleation of bubbles are
a possibility both in extensions of the Standard Model as well as in more
general hidden sectors. I will discuss the dynamics of expanding vacuum
bubbles in the presence of massive dark photons that gain mass across the
interface - with a special focus on the benchmark where they furnish the
dark matter. I will argue the existence of a transient relativistic regime
during which the wall can be thought of as an (imperfect) mirror of
longitudinal - but not transverse - vectors. This leads to a new source of
pressure on the expanding interface that can prevent the accelerated
expansion of the bubble walls. Instead, the energy released by the phase
transition goes into making the reflected dark photons relativistic. If
subsequent interactions with the environment can be ignored, an observable
contribution to \Delta N_eff is possible for strong phase transitions. Our
results highlight the potential interplay between the dark matter and the
dynamics of phase transitions in the early universe, as well as the
complementarity between gravitational wave detectors and CMB Stage-4

The agenda of this meeting is empty