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Constraints on the coupling with photons of heavy axion-like-particles from Globular Clusters

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 Added by Pierluca Carenza
 Publication date 2020
  fields Physics
and research's language is English




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We update the globular cluster bound on massive ($m_a$ up to a few 100 keV) axion-like particles (ALP) interacting with photons. The production of such particles in the stellar core is dominated by the Primakoff $gamma + Zeto Ze +a$ and by the photon coalescence process $gamma+gammato a$. The latter, which is predominant at high masses, was not included in previous estimations. Furthermore, we account for the possibility that axions decay inside the stellar core, a non-negligible effect at the masses and couplings we are considering here. Consequently, our result modifies considerably the previous constraint, especially for $m_a gtrsim 50$ keV. The combined constraints from Globular Cluster stars, SN 1987A, and beam-dump experiments leave a small triangularly shaped region open in the parameter space around $m_a sim 0.5-1,$ MeV and $g_{agamma} sim 10^{-5}$ GeV$^{-1}$. This is informally known as the ALP cosmological triangle since it can be excluded only using standard cosmological arguments. As we shall mention, however, there are viable cosmological models that are compatible with axion-like particles with parameters in such region. We also discuss possibilities to explore the cosmological triangle experimentally in upcoming accelerator experiments.



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114 - Giuseppe Lucente 2020
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 $g_{agamma} gtrsim 4 times 10^{-9}$ 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.
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We point out that stars in the mass window ~ 8-12 Msun can serve as sensitive probes of the axion-photon interaction, g_{Agammagamma}. Specifically, for these stars axion energy losses from the helium-burning core would shorten and eventually eliminate the blue loop phase of the evolution. This would contradict observational data, since the blue loops are required, e.g., to account for the existence of Cepheid stars. Using the MESA stellar evolution code, modified to include the extra cooling, we conservatively find g_{Agammagamma} <~ 0.8 * 10^{-10} GeV^{-1}, which compares favorably with the existing bounds.
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