Axions and the white dwarf luminosity function

TL;DR

This paper investigates whether axions, hypothetical particles, influence white dwarf cooling by comparing theoretical models with precise observational luminosity functions, suggesting axions may exist with specific mass ranges.

Contribution

It demonstrates that including axion emission in white dwarf models improves agreement with observations, providing potential evidence for axions.

Findings

Best fit axion mass around 2-6 meV

Values above 10 meV are excluded

Axions could influence white dwarf cooling

Abstract

The evolution of white dwarfs can be described as a simple cooling process. Recently, it has been possible to determine with an unprecedented precision their luminosity function, that is, the number of stars per unit volume and luminosity interval. Since the shape of the bright branch of this function is only sensitive to the average cooling rate, we use this property to check the possible existence of axions, a proposed but not yet detected weakly interacting particle. We show here that the inclusion of the axion emissivity in the evolutionary models of white dwarfs noticeably improves the agreement between the theoretical calculations and the observational white dwarf luminosity function, thus providing the first positive indication that axions could exist. Our results indicate that the best fit is obtained for m_a cos^2beta ~ 2-6 meV, where m_a is the mass of the axion and cos^2beta is a free parameter, and that values larger than 10 meV are clearly excluded.