Scalar Dark Matter Production through the Bubble Expansion Mechanism:The Role of the Lorentz factor and Non-Renormalizable Interactions

TL;DR

This paper investigates scalar dark matter production via bubble expansion during early Universe phase transitions, analyzing the effects of Lorentz factors and interactions, and finds viable production in low-velocity regimes with detectable gravitational waves.

Contribution

It introduces a comprehensive analysis of dark matter production through bubble expansion, including non-renormalizable interactions and low-velocity regimes, expanding previous parameter space understanding.

Findings

Dark matter can be produced efficiently even at low bubble wall velocities.

Non-renormalizable interactions yield similar dark matter abundances as renormalizable ones.

Gravitational wave signals from the transition are within future detector sensitivities.

Abstract

We consider a Bubble Expansion mechanism for the production of scalar dark matter during a first-order phase transition in the very early Universe. Seeking for a dark matter energy density in agreement with observations, we study different renormalizable and non-renormalizable interactions between the dark matter species and the field undergoing the transition, considering all possible regimes for the Lorentz boost factor associated with the motion of the bubble wall. By employing a combination of analytical and numerical techniques, we demonstrate that sufficient dark matter production is achievable even in the previously unexplored low-velocity bubble expansion regime, enlarging the parameter space and possibilities of the scenario. Notably, for the non-renormalizable interactions it is found that the produced dark matter abundances exhibit a similar qualitative behavior to the renormalizable case, even for low Lorentz boost factors. Furthermore, for a transition around the electroweak scale, the associated gravitational wave spectrum is within the reach of future detectors.