Particle-antiparticle asymmetries from annihilations

TL;DR

This paper explores how particle-antiparticle asymmetries can originate solely from 2<->2 annihilation processes, challenging the traditional focus on decay mechanisms, and provides a theoretical framework with a toy model.

Contribution

It introduces a novel mechanism for asymmetry generation via 2<->2 annihilations and formulates the corresponding Boltzmann equations with an illustrative example.

Findings

Conditions on reaction rates derived from unitarity and CPT invariance.

Formulation of Boltzmann equations for the annihilation-based asymmetry.

Example solution demonstrating the mechanism's viability.

Abstract

An extensively studied mechanism to create particle-antiparticle asymmetries is the out-of-equilibrium and CP violating decay of a heavy particle. Here we instead examine how asymmetries can arise purely from 2 <-> 2 annihilations rather than from the usual 1 <-> 2 decays and inverse decays. We review the general conditions on the reaction rates that arise from S-matrix unitarity and CPT invariance, and show how these are implemented in the context of a simple toy model. We formulate the Boltzmann equations for this model, and present an example solution.