Flavor-Violating Higgs Decays and Stellar Cooling Anomalies in Axion Models

Understand

We study a class of DFSZ-like models for the QCD axion that can address observed anomalies in stellar cooling.

• Stringent constraints from SN1987A and neutron stars are avoided by suppressed couplings to nucleons, while axion couplings to electrons and photons are sizable.
• All axion couplings depend on few parameters that also control the extended Higgs sector, in particular lepton flavor-violating couplings of the Standard Model-like Higgs boson $h$.
• This allows us to correlate axion and Higgs phenomenology, and we find that that ${\rm BR}(h \to \tau e)$ can be as large as the current experimental bound of 0.22%, while ${\rm BR} (h \to \mu \mu)$ can be larger than in the Standard Model by up to 70%.