Abstract
We provide an ultraviolet (UV) complete model for the R(D(∗)) anomalies, in which the additional contribution to semi-tauonic b → 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 × 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.
Highlights
All these simplified models may naively produce R(D(∗)) in approximate agreement with experiment
We provide an ultraviolet (UV) complete model for the R(D(∗)) anomalies, in which the additional contribution to semi-tauonic b → c transitions arises from decay to a right-handed sterile neutrino via exchange of a TeV-scale SU(2)L singlet W
We focus on the specific case of an SU(2)L singlet W -type mediator, which needs only carry a nonzero hypercharge. (This is in contrast to ref. [22] which focused on the colored leptoquark mediator, that is more accessible in the direct searches at the LHC.) As such, the W may obtain its mass from the spontaneous breaking of an exotic non-Abelian symmetry
Summary
We assume the SM field content is supplemented by a single new state, the right-handed sterile neutrino transforming as NR ∼ (1, 1, 0) under SU(3)c × SU(2)L × U(1)Y. This state may couple to the SM quarks via any of the four dimension-6 operators. The best fit value is obtained for C23,3 0.46 ± 0.06 (68% CL, ∆χ2 = 2.3) with minimum ∆χ2 1.0, to be compared with ∆χ2 20 at the SM point, C23,3 = 0. In figure 1 we show the corresponding exclusion region for |C23,3| (orange shaded regions), which is far from the best fit region
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