Aspects of particle production from bubble dynamics at a first order phase transition

First order phase transitions (FOPTs) constitute an active area of contemporary research as a promising cosmological source of observable gravitational waves. The spacetime dynamics of the background scalar field undergoing the phase transition can also directly produce quanta of particles that couple to the scalar, which has not been studied as extensively in the literature. This paper provides the first careful examination of various aspects of this phenomenon, which is important for understanding the dynamics of the phase transition, the generation of gravitational waves, and various high energy and beyond the Standard Model phenomena. In particular, the contributions from various stages of FOPTs (bubble nucleation, expansion, collision, postcollision) are disentangled, and conceptual aspects of the associated underlying physics relevant for particle production are clarified. Subtleties related to nonuniversality of particle interactions and masses in different vacua are discussed, and the suppression of nonperturbative effects such as tachyonic instability and parametric resonance due to the inhomogeneous nature of the process is examined.