Impact of axions on the Cassiopea A neutron star cooling

TL;DR

This study investigates how axion emission could influence the cooling rate of the Cassiopeia A neutron star, providing lower bounds on axion decay constants based on observational temperature data.

Contribution

It introduces constraints on axion models by analyzing their impact on neutron star cooling, using updated observational data and minimal neutrino cooling scenarios.

Findings

Lower limit on axion decay constant for KSVZ model: >3×10^7 GeV

Lower limit on axion decay constant for DFSZ model: >4.5×10^8 GeV

Axion emission can significantly affect neutron star cooling rates.

Abstract

The observed anomalous steady decrease in surface temperature of the supernova remnant Cassiopeia A (Cas A), which was reported about ten years ago, has generated much debate. Several exotic cooling scenarios have been proposed using non-standard assumptions about the physics and evolution of this neutron star (NS). At present, significant corrections have been made to the observational data, which make it possible to numerically simulate the Cas A NS cooling process in the framework of the scenario of minimal neutrino cooling. If there is an additional source of cooling, such as axion emission, the steepness of the Cas A NS surface temperature drop will increase with the growth of the axion-nucleon interaction strength. This makes it possible to limit the minimum value of the axion decay constant $f_a$ using the condition that the NS surface temperature should be within the 99% confidence interval obtained from the observational data. Two types of axion models are considered: the Kim-Shifman-Weinstein-Zakharov -- KSVZ model and the Dean-Fischler-Srednitsky-Zhitnitsky --DFSZ model. The above criterion gives a lower limit on the axion decay constant, $f_a>3\times 10^7$ GeV and $f_a>4.5\times 10^8$ GeV for KSVZ and DFSZ axions, respectively.