Ultrahigh-Energy Particle Collisions and Heavy Dark Matter at Phase Transitions

Abstract

We initiate the study of "bubbletrons," by which we mean ultrahigh-energy collisions of the particle shells that generically form at the walls of relativistic bubbles in cosmological first-order phase transitions (PT). As an application, we calculate the maximal dark matter mass M_{DM} that bubbletrons can produce in a U(1) gauge PT, finding M_{DM}∼10^{5}/10^{11}/10^{15} GeV for PT scales v_{ϕ}∼10^{-2}/10^{3}/10^{9} GeV. Bubbletrons realize a novel link between ultrahigh-energy phenomena and gravitational waves sourced at the PT, from nanohertz to megahertz frequencies.