Astrophobic Axions

Abstract

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. Astrophysical limits are thus relaxed, allowing for axion masses up to O(0.1) eV. The axion-photon coupling remains instead sizable, so that next-generation helioscopes will be able to probe this scenario. Astrophobia unavoidably implies flavor-violating axion couplings so that experimental limits on flavor-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.

Axion-electron decoupling in nucleophobic axion models

“…In the arXiv:1907.06575v1 [hep-ph] 15 Jul 2019 first line, 1 = f u + f d is an exact number, while δ s = 0.038 C s +0.012 C c +0.009 C b +0.0035 C t is a small O(5%) correction dominated by the s-quark contribution. Nucleophobia requires C p ± C n ≈ 0, which is possible in variant DFSZ models with two Higgs doublets H 1,2 and non-universal PQ charge assignment [1]. To see this, let us focus on the first generation Yukawa terms…”

“…It has been recently argued [1] that in variants of Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) [2,3] models with two Higgs doublets and generation-dependent Peccei Quinn (PQ) charges, it is possible to strongly suppress axion couplings to nucleons (axion nucleophobia). This implies that the upper limit on the DFSZ axion mass from the neutrino burst duration of the supernova (SN) SN1987A, which is particularly strong and generally considered ineludible, can in fact be sizeably relaxed.…”

“…This implies that the upper limit on the DFSZ axion mass from the neutrino burst duration of the supernova (SN) SN1987A, which is particularly strong and generally considered ineludible, can in fact be sizeably relaxed. 1 The parameter space region that opens up for nucleophobic axions is, however, only marginal. This is because in DFSZ models the axion also couples to electrons, and then limits from anomalous cooling of white dwarfs and red giants, which are only moderately less restrictive, apply.…”

Flavour Violating Axions

“…While the second condition can always be implemented via a tuning (see below), the real bottleneck is the first one, since X u = X d = 0 in KSVZ models, while in DFSZ models one has N = 1 2 n f (2X Q 1 − X u 1 − X d 1 ) = n f (X u + X d ), with n f = 3 denoting the number of families. The above no-go theorem for standard axion models suggests itself a possible way out [26]: if the total anomaly factor were equal to that of the first family, i.e. N = N 1 = X u + X d , the first condition would be automatically satisfied.…”

“…E/N = {−4/3, 2/3, 8/3, 14/3} in the models of Ref. [26], so that the next generation of helioscopes, such as IAXO [33], will be able to probe their parameter space.…”