Year: 1997
Type: article
Abstract: A particular class of variant axion models with two Higgs doublets and a singlet is studied. In these models the axion couples either to the $u$ quark or $t$ quark or both, but not to $b,$ $c,$ $s,$ or $d.$ When the axion couples to only one quark the models possess the desirable feature of having no domain wall problem, which makes them viable candidates for a cosmological axion string scenario. We calculate the axion couplings to leptons, photons, and nucleons, and the astrophysical constraints on the axion decay constant ${v}_{a}$ are investigated and compared to the Dine-Fischler-Srednicki-Zhitnitskii (DFSZ) axion model. We find that the most restrictive lower bound on ${v}_{a},$ that from SN 1987A, is lowered by up to a factor of about 35, depending on the model and also the ratio of the vacuum expectation values of the Higgs doublets. For scenarios with axionic strings, the allowed window for ${v}_{a}$ in the $u$ quark model can be more than two orders of magnitude. For inflationary scenarios, the cosmological upper bound on ${v}_{a}/N,$ where $N$ is the QCD anomaly factor, is unaffected: however, the variant models have $N$ either 3 or 6 times smaller than the DFSZ model.
Authors: Mark Hindmarsh, Photis Moulatsiotis
Institution: University of Sussex
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2135078596