CP-violation in production of heavy neutrinos from bubble collisions

TL;DR

This paper systematically analyzes CP-violation mechanisms during early Universe bubble collisions, exploring their implications for baryon asymmetry, dark matter, neutrino masses, and gravitational wave signals detectable by future observatories.

Contribution

It introduces a comprehensive analysis of CP-violation channels in bubble collisions and presents a simple cogenesis model linking baryon asymmetry and dark matter.

Findings

CP-violation can occur via decay, production of heavy particles, or production of SM particles during bubble collisions.

A cogenesis model explains baryon asymmetry and dark matter abundance through lepton number asymmetries.

Future gravitational wave detectors like the Einstein Telescope can probe significant parts of the model's parameter space.

Abstract

First order phase transitions (FOPT) in the early Universe can be powerful emitters of both relativistic and heavy particles, upon the collision of ultra-relativistic bubble shells. If the particles coupling to the bubble wall have CP-violating interactions, the same collision process can also create a local lepton or baryon charge. This CP-violation can originate from different channels, which have only been partially addressed in the literature. We present a systematic analysis of the different channels inducing CP-violation during bubble collisions: 1) the decay of heavy particles 2) the production of heavy particles and 3) the production of light and relativistic Standard Model (SM) particles. As an illustration of the impact that such mechanisms can have on baryon number and dark matter (DM) abundance, we then introduce a simple model of cogenesis, separating a positive and a negative lepton number in the SM and a dark sector (DS). The lepton number asymmetry in the SM can be used to explain the baryon asymmetry of the Universe (BAU), while the opposite asymmetry in the DS is responsible for determining the abundance of DM. Moreover, the masses of light neutrinos can be understood via the inverse seesaw mechanism, with the lepton-violating Majorana mass originating from the FOPT. A typical signal produced by a FOPT is the irreducible gravitational wave (GW) background. We find that a substantial portion of the parameter space can be probed at future observatories like the Einstein Telescope (ET).