Abstract
We propose a class of axion models with generation dependent Peccei-Quinn charges for the known fermions that allow to suppress the axion couplings to nucleons and electrons. Astrophysical limits are thus relaxed, allowing for axion masses up to ${\cal O}(0.1)$ eV. The axion-photon coupling remains instead sizeable, so that next generation helioscopes will be able to probe this scenario. Astrophobia unavoidably implies flavor violating axion couplings, so that experimental limits on flavour-violating processes can provide complementary probes. The astrophobic axion can be a viable dark matter candidate in the heavy mass window, and can also account for anomalous energy loss in stars.
Highlights
Introduction.—One of the main mysteries of the standard model (SM) is the absence of CP violation in strong interactions
The most elegant solution is provided by the Peccei-Quinn (PQ) mechanism [1,2], which predicts the axion as a low-energy remnant [3,4]
The KimShifman-Vainshtein-Zakharov (KSVZ) [5,6] and DineFischler-Srednicki-Zhitnitsky (DFSZ) [7,8] axion models are frequently used as benchmarks to assess experimental sensitivities and to derive astrophysical bounds
Summary
Luca Di Luzio, Federico Mescia, Enrico Nardi, Paolo Panci, and Robert Ziegler. We propose a class of axion models with generation-dependent Peccei-Quinn charges for the known fermions that allow one to suppress the axion couplings to nucleons and electrons. While it is conceptually easy to build models with suppressed axionelectron couplings gae [5,6,9] or axion-photon couplings gaγ [10,11,12], it is generally believed that a robust prediction of all axion models is an unsuppressed axion-nucleon coupling gaN This is important, because gaN is responsible for the often-quoted bound on the axion mass ma ≲ 20 meV from the neutrino burst duration of SN1987A [13,14]. Nucleophobia allows one to relax the SN bound, and electrophobia allows one to evade the WD and RG constraints, rendering viable ma ∼ Oð0.1Þ eV We denote such an axion as astrophobic, gaγ remains generically sizable and could still affect the evolution of horizontal branch (HB) stars.
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