Particle production from bubble collisions
arXiv:2607.15279
The paper investigates how ultra‑relativistic bubble collisions during cosmological phase transitions can generate very heavy particles, introducing a partonic‑like formalism based on on‑shell scatterings of wall quanta and applying it to scalar, fermion, and vector production with relevance for dark matter, leptogenesis, and primordial gravitational waves.
Abstract
Collisions of ultra-relativistic bubbles during cosmological phase transitions can produce particles much heavier than the transition scale. Previous analyses modelled this process as the off-shell decay of the scalar background. We show that its results parametrically overestimate hard particle production and depend on the gauge choice and the coordinate choice in field space. We propose an alternative formalism, analogous to the partonic description of high-energy collisions. In the ultra-relativistic limit, the colliding bubbles undergo nearly free passage and hard production arises from on-shell scatterings among the quanta constituting the Lorentz-contracted walls. We apply this approach to heavy scalar, fermion, and vector particle production, and study the implications for dark matter, leptogenesis, graviton production and primordial gravitational waves.
31 pages, 9 figures. Webinar presentation: https://youtu.be/jmshs9YXn9g