$R(D^{(*)})$ from $W'$ and right-handed neutrinos

Abstract

We provide an ultraviolet (UV) complete model for the $R(D^{(*)})$ anomalies, in which the additional contribution to semi-tauonic $b \to c$ transitions arises from decay to a right-handed sterile neutrino via exchange of a TeV-scale $SU(2)_L$ singlet $W'$. The model is based on an extension of the Standard Model (SM) hypercharge group, $U(1)_Y$, to the $SU(2)_V\times U(1)'$ gauge group, containing several pairs of heavy vector-like fermions. We present a comprehensive phenomenological survey of the model, ranging from the low-energy flavor physics, direct searches at the LHC, to neutrino physics and cosmology. We show that, while the $W'$ and $Z'$-induced constraints are important, it is possible to find parameter space naturally consistent with all the available data. The sterile neutrino sector also offers rich phenomenology, including possibilities for measurable dark radiation, gamma ray signals, and displaced decays at colliders.