Predictions for Axion Couplings from ALP Cogenesis

TL;DR

This paper proposes a model where an axion-like particle (ALP) explains both baryon asymmetry and dark matter density, predicting specific couplings that are testable by future experiments.

Contribution

It introduces ALP cogenesis, linking ALP properties to cosmological observations and providing testable predictions for ALP couplings.

Findings

Predicted ALP couplings are significantly larger than QCD axion predictions.

ALP cogenesis links ALP mass and decay constant to cosmological densities.

Predictions are within reach of upcoming experimental searches.

Abstract

Adding an axion-like particle (ALP) to the Standard Model, with a field velocity in the early universe, simultaneously explains the observed baryon and dark matter densities. This requires one or more couplings between the ALP and photons, nucleons, and/or electrons that are predicted as functions of the ALP mass. These predictions arise because the ratio of dark matter to baryon densities is independent of the ALP field velocity, allowing a correlation between the ALP mass, $m_a$, and decay constant, $f_a$. The predicted couplings are orders of magnitude larger than those for the QCD axion and for dark matter from the conventional ALP misalignment mechanism. As a result, this scheme, ALP cogenesis, is within reach of future experimental ALP searches from the lab and stellar objects, and for dark matter.