Shining ALP dark radiation
PHYSICAL REVIEW D(2022)
摘要
String scenarios typically not only predict axionlike particles (ALPs) but also significant amounts of ALP dark radiation originating from the decay of the inflaton or a more general modulus. In this paper, we study the decay of such nonthermally produced relativistic (but massive) ALPs to photons. If the ALPs are sufficiently highly energetic, contribute to Delta N-eff greater than or similar to O(0.001), and have a mass m(a) greater than or similar to MeV we find that, using observations of x-, and gamma-rays, the CMB and BBN, very small values of the ALP-photon coupling, can be probed, corresponding to an origin of this coupling at the string (or even Planck) scale.
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