Impacts of axion cooling on the direct detection of supernova axions

TL;DR

This work addresses the uncertainty in predicting direct detection rates for supernova axions by explicitly coupling axion emission to long-term, general-relativistic simulations of a $9.6\,M_\odot$ progenitor. Using the KSVZ model and a many-body suppression of axion emissivity, the authors compute self-consistent axion luminosities $L_a$ and expected helioscope event numbers, demonstrating a strong nonlinear feedback: axion cooling lowers the core temperature and suppresses $L_a$, reducing detection prospects relative to post-processing estimates. The results show a peak axion luminosity near post-bounce times $t_\mathrm{pb}\sim1$--$2$ s, but with heavier axions the central temperature declines substantially (e.g., from $\sim30$ MeV to $\sim12$ MeV by $t_\mathrm{pb}=10$ s), causing $Q_a$ to drop by orders of magnitude at late times and hastening the decay of the axion signal. Consequently, for a Betelgeuse-like nearby SN, the asymptotic axion event number remains $N<1$ up to $m_a=11$ meV when cooling is included, whereas post-processing would overestimate detectability; this underscores the importance of self-consistent feedback and motivates systematic studies across progenitors and equations of state.

Abstract

Core-collapse supernovae provide a unique opportunity to probe axions because they can be a copious source of the particles. It has recently been proposed that axion helioscopes can be used for the direct search for supernova axions if a supernova event appears within a few hundred parsecs. However, the event number of supernova axions has been estimated only within the post-process framework. In this study, we perform long-term supernova simulations for a 9.6M_sun star coupled with the axion emission to reevaluate the event number of axions detected by the helioscopes. We find that the additional cooling induced by the axion emission can significantly decrease the temperature in the proto-neutron star. As a result, the axion luminosity and hence the axion event number are reduced, compared with the result obtained through post-processing. Our result indicates that the nonlinear feedback of the axion emission is an essential factor to predict the axion detectability, and underscores the need for systematic simulation studies across various progenitor models.

Figures (6)

• Figure 1: The axion luminosity for each model is shown in the broken curves. The solid curve is the neutrino luminosity for the reference model without axions.
• Figure 2: The neutrino luminosity for each model. The left panel focuses on the early phase at $t_\mathrm{pb}\in[-0.05,\,0.3]$ s and the right panel shows the late phase at $t_\mathrm{pb}\in[0,\,15]$ s. The solid curve represents the result for the reference model without axions and the broken curves represent the results with axions.
• Figure 3: The temperature (left panel) and $Q_\mathrm{a}$ (right panel) profiles. The solid curves are the results for the $m_a=10$ meV model and the broken curves are for the reference model without the axion cooling effect. In the right panel, $Q_a$ for the reference model is estimated with the post-processing technique, assuming $m_a=10$ meV.
• Figure 4: The cumulative event number for axions observed with the IAXO upgraded scenario. The supernova event of Betelgeuse, which is located at $d\approx168$ pc, is assumed. The solid curves show the result with the axion cooling effect and the broken curves are the results without the effect.
• Figure 5: The asymptotic event number of axions as a function of the axion luminosity $L_a$ at $t_\mathrm{pb}=1$ s. The left panel is based on the self-consistent simulations and the right panel is based on the post-processing. Each curve represents the results with different distances to the supernova event. The IAXO upgraded scenario is assumed as the detector. The vertical line at $L_a=3\times10^{52}$ erg s$^{-1}$ is an upper limit on the axion luminosity based on the SN 1987A neutrino burst 1990PhR...198....1R.