Abstract
The axion search experiments invite a plausible estimation of the axion–photon–photon coupling constant c¯aγγ in string models with phenomenologically acceptable visible sectors. We present the calculation of c¯aγγ with an exact Peccei–Quinn symmetry. In the Huh–Kim–Kyae Z12−I orbifold compactification, we obtain c¯aγγ=1123388, and the low-temperature axion search experiments will probe the QCD corrected coupling, caγγ≃c¯aγγ−1.98≃0.91.
Highlights
ArXiv:1405.6175v5 [hep-ph] 15 Jan 2015. It seems that the Universe once passed the grand unification (GUT) scale energy region with its imprint survived until now [1]
If this BICEP2 result on the B-mode polarization survives on the matter of GUT scale energy density during inflation, it has a far-reaching implication in axion cosmology [2, 3]
We computed the axion–photon–photon coupling in a phenomenologically viable HKK SU(5)flip×SU(5)′×U(1)anom model from the heterotic E8×E′8 string compactified on the Z12−I orbifold, caγγ = 8/3 even with a lot of singlets at the GUT scale, leading to c2aγγ ≃ 0.47
Summary
It seems that the Universe once passed the grand unification (GUT) scale energy region with its imprint survived until now [1]. A string theory solution of the domain wall problem is possible [4] using a discrete subgroup of the anomalous U(1) symmetry in string models. We calculate the axion–photon-photon coupling strength, which is needed as a guideline in the axion detection experiments It is in the Huh-Kim-Kyae (HKK) double SU(5) model [23, 24] from Z12−I orbifold compactification. We emphasized that the early history of the Universe does not take the possibility of inflating away the topological defects of axion models [4] This implies that the axion solution of the strong CP problem via the spontaneous breaking of the Peccei-Quinn (PQ) symmetry is cosmologically disfavored if the axion domain wall number is not one [33].
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