Heavy axion-like particles and core-collapse supernovae: constraints and impact on the explosion mechanism

Abstract: Heavy axion-like particles (ALPs), with masses $m_a \gtrsim 100$ keV, coupled with photons, would be copiously produced in a supernova (SN) core via Primakoff process and photon coalescence. Using a state-of-the-art SN model, we revisit the energy-loss SN 1987A bounds on axion-photon coupling. Moreover, we point out that heavy ALPs with masses $m_a \gtrsim 100$ MeV and axion-photon coupling $g_{a\gamma} \gtrsim 4 \times 10^{-9}$ GeV$^{-1}$ would decay into photons behind the shock-wave producing a possible enhancement in the energy deposition that would boost the SN shock revival.

Heavy Axion-like Particles and Supernova Explosion Mechanism

This paper investigates the potential role of heavy axion-like particles (ALPs) in core-collapse supernovae (SNe), specifically focusing on the energy-loss bounds from SN 1987A and the implications for ALPs on the supernova explosion mechanism. The authors study ALPs with masses $m_a \gtrsim 100$ keV, coupled with photons, which could be produced in supernova cores via the Primakoff process and photon coalescence.

ALP Production Processes and Implications

The authors used state-of-the-art SN models to evaluate the implications of ALP production on the energy balance within supernovae. The dominant production mechanism in dense SN cores is via the Primakoff process, where thermal photons convert to ALPs in the electric field of protons. In regions of high density, two photons may annihilate to produce an ALP through photon coalescence. This paper examines both processes, emphasizing that for ALPs with masses above $100$ MeV, coalescence becomes more significant compared to previous studies that largely neglect it.

Energy-loss Bounds from SN 1987A

Utilizing simulation data, the paper revisits energy-loss bounds from SN 1987A, suggesting energy carried away by ALPs should not exceed that of neutrinos. The derived numerical constraint is $L_a \lesssim 3 \times 10^{52}$ erg s$^{-1}$ at $t_{\text{pb}} = 1$ s. They also incorporate the notion of modified luminosity by considering only ALP energy loss occurring beyond the neutrino sphere.

ALP Decay and Potential Shock Revival

The decay of heavy ALPs into photons post-shock wave could enhance energy deposition encouraging shock revival and the supernova explosion. While traditional models rely on neutrino heating, this paper speculates the contribution from ALPs decaying behind the shock-wave could provide additional pressure to aid the revival of shock waves, which is particularly interesting in spherically symmetric simulations where maintaining explosion energy is challenging.

Numerical Insights and Theoretical Considerations

The authors found that ALP emissivity peaks around $r \sim 10$ km in the SN core, with a production region identified between $5$-$15$ km. The mass-dependent production highlights that for masses $m_a \gtrsim 100$ MeV, photon coalescence is significant and relevant to constraints on ALP-photon coupling $g_{a\gamma}$. They include gravitational trapping effects on ALP production, suggestive of dependency on the progenitor mass used in the SN models.

Implications and Future Research Directions

The paper suggests future investigations could focus on the role of ALPs in multidimensional simulations to better understand their potential contribution to explosion mechanisms. Additionally, the authors highlight the need for further simulations including ALP feedback effects to refine bounds and assess their true impact on the supernova dynamics.

Overall, this study provides updated constraints on ALPs' couplings from SN 1987A observations and theorizes their possible contribution to the energy dynamics driving supernova explosions. The exploration of both theoretical and practical implications opens avenues for further research in the field of astroparticle physics, especially concerning the mechanisms underpinning supernova phenomena.