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 important aspects of this phenomenon. In particular, the contributions from various stages of FOPTs (bubble nucleation, expansion, collision) are disentangled. It is demonstrated that heavy particles primarily originate from the relative motion of bubble walls at distances comparable to the Compton wavelength of the particle rather than from the bubble collision itself. Subtleties related to non-universality of particle interactions and masses in different vacua are discussed, and a prescription to choose the correct vacuum for the calculation is provided. The suppression of non-perturbative effects such as tachyonic instability and parametric resonance due to the inhomegeneous nature of the process is examined.