Cosmological abundance of the QCD axion coupled to hidden photons

Abstract

We study the cosmological evolution of the QCD axion coupled to hidden photons. For a moderately strong coupling, the motion of the axion field leads to an explosive production of hidden photons by tachyonic instability. We use lattice simulations to evaluate the cosmological abundance of the QCD axion. In doing so, we incorporate the backreaction of the produced hidden photons on the axion dynamics, which becomes significant in the non-linear regime. We find that the axion abundance is suppressed by at most O(10 2 ) for the decay constant fa = 10 16 GeV, compared to the case without the coupling. For a sufficiently large coupling, the motion of the QCD axion becomes strongly damped, and as a result, the axion abundance is enhanced. Our results show that the cosmological upper bound on the axion decay constant can be relaxed by a few hundred for a certain range of the coupling to hidden photons. PACS numbers: 25.75.Dw, 14.80.Mz, 95.35.+d

Audible axions

“…We note that in this work we ignore the backscattering of the gauge fields which can induce inhomogeneities in the axion field. A recent study suggests that including this effect could make the suppression of the axion relic abundance less efficient [22]. This will not have a dramatic impact on the GW signal, since it is dominantly produced during the large initial drop in the axion energy density.…”

A two particle hidden sector and the oscillations with photons

“…However, there can be distinctive features in other kind of laboratory experiments, such as ADMX [27] if either or both of them are dark matter candidates. This study is left as a future work, although there are already some interesting results pointing into that direction [28].…”

Axionlike particle constraints in gauged N=2 supergravity

“…One of them (Z 1 ) is responsible to interactions within either dark or normal sector themselves, while the other one (Z 2 ) interacts with both sectors at once. These features seem interesting in terms of the several applications of axion-photon-hidden photon, and axion-double hidden photon couplings, which are discussed in e.g., [38][39][40][41][42][43][44][45].…”