Abstract
We explore scenarios where the R(D(∗)) anomalies arise from semitauonic decays to a right-handed sterile neutrino. We perform an EFT study of all five simplified models capable of generating at tree-level the lowest dimension electroweak operators that give rise to this decay. We analyze their compatibility with current R(D(∗)) data and other relevant hadronic branching ratios, and show that one simplified model is excluded by this analysis. The remainder are compatible with collider constraints on the mediator semileptonic branching ratios, provided the mediator mass is of order TeV. We also discuss the phenomenology of the sterile neutrino itself, which includes possibilities for displaced decays at colliders and direct searches, measurable dark radiation, and gamma ray signals.
Highlights
Ντ is the SM left-handed τ neutrino, and via a new decay channel, b → cτ NR, where NR is a sterile right-handed neutrino
Assuming first that all Wilson coefficients are real, we show in figure 2 the 0.5σ, 1σ CLs and 1.5σ, 2σ CLs in the relevant Wilson coefficient spaces for each simplified model
We have performed an EFT study of the lowest dimension electroweak operators that can account for the R(D(∗)) anomalies, assuming they arise because of incoherent contributions from semitauonic decays involving a right-handed sterile neutrino NR
Summary
We consider the extension of the SM field content by a single new state, a right handed, sterile neutrino transforming as NR ∼ (1, 1, 0) under SU(3)c × SU(2)L × U(1)Y. Assuming first that all Wilson coefficients are real, we show in figure 2 the 0.5σ, 1σ CLs (dark, light blue) and 1.5σ, 2σ CLs (dark, light green) in the relevant Wilson coefficient spaces for each simplified model These CLs are generated by the χ2 defined with respect to the R(D(∗)) experimental data and correlations (2.14), not including the possible effects of NP errors. In the single mediator exchange models, this means that the product αL3 dαQ2 N for R2 and the product zd3zQ2 for S1 (and yd for Φ) need to be much smaller than what is required to explain R(D(∗)) This excludes the R2 as a simple one mediator solution to R(D(∗)): additional operators coupling to the second generation of quark doublets must be introduced, whose couplings are tuned appropriately to suppress the contributions to b → sνν.
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