CERN Accelerating science

Article
Report number	arXiv:2004.08399
Title	Constraints on the coupling with photons of heavy axion-like-particles from Globular Clusters
Author(s)	Carenza, Pierluca (Bari U. ; INFN, Bari) ; Straniero, Oscar (Rome Observ.) ; Döbrich, Babette (CERN) ; Giannotti, Maurizio (Barry U.) ; Lucente, Giuseppe (Bari U.) ; Mirizzi, Alessandro (Bari U. ; INFN, Bari)
Publication	2020-10-10
Imprint	2020-04-17
Number of pages	10
Note	10 pages, 5 figures. v2: Revised version. Matches the version published on PLB. Improved the discussion on axion energy transfer in HB stars. Added two Appendices on photon-axion transition rate from Primakoff conversion and on photon coalescence
In:	Phys. Lett. B 809 (2020) 135709
DOI	10.1016/j.physletb.2020.135709 (publication)
Subject category	hep-ex ; Particle Physics - Experiment ; astro-ph.SR ; Astrophysics and Astronomy ; hep-ph ; Particle Physics - Phenomenology
Abstract	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 $\gamma + Ze\to Ze +a$ and by the photon coalescence process $\gamma+\gamma\to a$. 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 $g_{a\gamma} \sim 10^{-5}$ 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.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: The Author(s) (License: CC-BY-4.0)

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