Limit on the Axion Decay Constant from the Cooling Neutron Star in Cassiopeia A

TL;DR

This paper investigates how axion emission could influence the rapid cooling of the Cassiopeia A neutron star, deriving a lower limit on the axion decay constant comparable to other astrophysical constraints.

Contribution

It provides the first detailed analysis of axion emission effects on the entire cooling history of the Cas A neutron star, establishing new bounds on the axion decay constant.

Findings

Lower limit on axion decay constant: $f_a\gtrsim (5-7)\times 10^8$ GeV

Axion emission can significantly affect neutron star cooling

Results comparable to constraints from SN1987A

Abstract

The observed rapid cooling of the neutron star (NS) located at the center of the supernova remnant Cassiopeia A (Cas A) can be explained in the minimal NS cooling scenario. This consequence may be changed if there exists an extra cooling source, such as axion emission. In this work, we study the Cas A NS cooling in the presence of axion emission, taking account of the temperature evolution in the whole life of the Cas A NS. We obtain a lower limit on the axion decay constant, $f_a\gtrsim (5-7)\times 10^8$ GeV, if the star has an envelope with a thin carbon layer. This is as strong as existing limits imposed by other astrophysical observations such as SN1987A.