Impact of Bound State Formation on Baryogenesis

TL;DR

This paper investigates how the formation of bound states among heavy particles with long-range interactions can significantly influence baryogenesis, affecting particle abundances, asymmetry sources, and washout processes.

Contribution

It provides the first formulation of Boltzmann equations incorporating bound state effects in baryogenesis models and outlines conditions for their significance.

Findings

Bound states can alter particle abundances relevant to BAU

They can serve as additional sources of baryon asymmetry

Bound states mediate new washout channels affecting BAU

Abstract

The mechanism behind the generation of the baryon asymmetry of the Universe (BAU) is one of the biggest open questions of (astro-)particle physics. Popular mechanisms to generate the observed baryon asymmetry include CP-violating out-of-equilibrium decays and scatterings of heavy particles. If these heavy non-relativistic particles feature long-range interactions, the formation of bound states can impact the generation of the baryon asymmetry. We outline the general conditions for when bound states are important for decay and scattering dominated baryogenesis and present the necessary Boltzmann equations for the first time. We demonstrate that bound states can impact baryogenesis in three different ways: They (i) strongly impact abundances of particles sourcing the BAU, (ii) act as a source term of the asymmetry, and (iii) mediate additional washout channels.