Oscillating Asymmetric Dark Matter

TL;DR

This paper investigates how dark matter particles oscillate between particle and antiparticle states due to small Majorana mass terms, affecting their relic density and annihilation processes, with new density matrix equations derived from first principles.

Contribution

It introduces a novel, first-principles derivation of density matrix equations for asymmetric dark matter oscillations, revealing new flavor-dependent effects and differences from previous models.

Findings

Flavor-sensitive annihilation does not recouple during oscillations.

Flavor-blind scattering does not cause decoherence.

Oscillations can lead to recoupling and washout of dark matter density.

Abstract

We study the dynamics of dark matter (DM) particle-antiparticle oscillations within the context of asymmetric DM. Oscillations arise due to small DM number-violating Majorana-type mass terms, and can lead to recoupling of annihilation after freeze-out and washout of the DM density. We derive the density matrix equations for DM oscillations and freeze-out from first principles using nonequilibrium field theory, and our results are qualitatively different than in previous studies. DM dynamics exhibits particle-vs-antiparticle "flavor" effects, depending on the interaction type, analogous to neutrino oscillations in a medium. "Flavor-sensitive" DM interactions include scattering or annihilation through a new vector boson, while "flavor-blind" interactions include scattering or s-channel annihilation through a new scalar boson, or annihilation to pairs of bosons. In particular, we find that flavor-sensitive annihilation does not recouple when coherent oscillations begin, and that flavor-blind scattering does not lead to decoherence.