In F-theory GUTs, non-universal ALPs induced by hypercharge flux satisfy g_aγ/m_a well below the QCD axion prediction when gauge couplings unify near the string scale.
Resonant conversions of QCD axions into hidden axions and suppressed isocurvature perturbations
4 Pith papers cite this work. Polarity classification is still indexing.
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abstract
We study in detail MSW-like resonant conversions of QCD axions into hidden axions, including cases where the adiabaticity condition is only marginally satisfied, and where anharmonic effects are non-negligible. When the resonant conversion is efficient, the QCD axion abundance is suppressed by the hidden and QCD axion mass ratio. We find that, when the resonant conversion is incomplete due to a weak violation of the adiabaticity, the CDM isocurvature perturbations can be significantly suppressed, while non-Gaussianity of the isocurvature perturbations generically remain unsuppressed. The isocurvature bounds on the inflation scale can therefore be relaxed by the partial resonant conversion of the QCD axions into hidden axions.
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Multi-axion solutions to the strong CP problem produce varied mass-coupling patterns set by PQ symmetry breaking structure and QCD-EM anomaly alignment, summarized by a general sum rule for N-axion systems.
Multi-axion models relax the E/N bound on QCD axion photon coupling and allow subdominant dark matter contribution, but an axion-like particle is typically visible to next-generation experiments.
Double level crossings are common in multi-axion mass mixing of Z_N axions and ALPs, occurring multiple times for large N in the light axion case but prevented by excessively large or small N in light and heavy scenarios respectively.
citing papers explorer
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Testing F-theory GUTs with the Axiverse
In F-theory GUTs, non-universal ALPs induced by hypercharge flux satisfy g_aγ/m_a well below the QCD axion prediction when gauge couplings unify near the string scale.
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The structure of multi-axion solutions to the strong CP problem
Multi-axion solutions to the strong CP problem produce varied mass-coupling patterns set by PQ symmetry breaking structure and QCD-EM anomaly alignment, summarized by a general sum rule for N-axion systems.
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How well can the QCD axion hide?
Multi-axion models relax the E/N bound on QCD axion photon coupling and allow subdominant dark matter contribution, but an axion-like particle is typically visible to next-generation experiments.
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Completing Axion Double Level Crossings
Double level crossings are common in multi-axion mass mixing of Z_N axions and ALPs, occurring multiple times for large N in the light axion case but prevented by excessively large or small N in light and heavy scenarios respectively.