Strong bound on canonical ultra-light axion dark matter from the Lyman-alpha forest

TL;DR

This paper establishes a new lower bound on ultra-light axion dark matter mass using Lyman-alpha forest data, significantly constraining the canonical axion models and improving previous bounds with robust simulations.

Contribution

It provides the strongest lower limit to date on ultra-light axion mass using advanced hydrodynamical simulations and Lyman-alpha forest observations.

Findings

Lower bound on axion mass: > 2 x 10^{-20} eV at 95% confidence

Disfavors canonical axion models with 10^{-22} to 10^{-21} eV

Improves previous bounds by about an order of magnitude

Abstract

We present a new bound on the ultra-light axion (ULA) dark matter mass $m_\text{a}$, using the Lyman-alpha forest to look for suppressed cosmic structure growth: a 95% lower limit $m_\text{a} > 2 \times 10^{-20}\,\text{eV}$. This strongly disfavors ($> 99.7\%$ credibility) the canonical ULA with $10^{-22}\,\text{eV} < m_\text{a} < 10^{-21}\,\text{eV}$, motivated by the string axiverse and solutions to possible tensions in the cold dark matter model. We strengthen previous equivalent bounds by about an order of magnitude. We demonstrate the robustness of our results using an optimized emulator of improved hydrodynamical simulations.