Cosmological bounds on pseudo Nambu-Goldstone bosons

TL;DR

This paper reviews how relic pseudo Nambu-Goldstone bosons, or axion-like particles, impact cosmology and establishes constraints on their properties using data from big bang nucleosynthesis, CMB, and photon backgrounds.

Contribution

It provides new cosmological bounds on pNGB mass and coupling, improving constraints through analysis of multiple cosmological observations.

Findings

Bounds from WMAP7 and large-scale structure are stronger than helium bounds.

Primordial deuterium abundance provides significant constraints.

Combined bounds are the most stringent probes of early pNGB decays.

Abstract

We review the cosmological implications of a relic population of pseudo Nambu-Goldstone bosons (pNGB) with an anomalous coupling to two photons, often called axion-like particles (ALPs). We establish constraints on the pNGB mass and two-photon coupling by considering big bang nucleosynthesis, the physics of the cosmic microwave background, and the diffuse photon background. The bounds from WMAP7 and other large-scale-structure data on the effective number of neutrino species can be stronger than the traditional bounds from the primordial helium abundance. These bounds, together with those from primordial deuterium abundance, constitute the most stringent probes of early decays.