Anatomy of b → c τ ν anomalies

Abstract

In recent times, one of the strongest hints of Physics Beyond the Standard Model (BSM) has been the anomaly in the ratios R D and R D * measured in the charged current decays of B-mesons. In this work, we perform a comprehensive analysis of these decay modes, first in a model independent way and subsequently, in the context of composite Higgs models. We discuss in depth as to how linearly realised SU(2) L × U(1) Y symmetry imposes severe constraint on the various scenarios because of correlations with other ∆F = 1 processes and Z τ τ and Z ν ν couplings. In the composite Higgs paradigm with partial compositeness, we show that, irrespective of the flavour structure of the composite sector, constraints from ∆F = 2 processes bring the compositeness scale down to ∼ 650 GeV which is in tension with electroweak precision observables. In the presence of composite leptoquarks, the situation improves only marginally (a factor of √ 2 in the compositeness scale), thus making the new states soon discoverable by direct searches at the LHC. We also comment on the possible explanation of the R K,K * anomalies within the composite Higgs framework.

B -meson charged current anomalies: The post-Moriond 2019 status

“…We remind the readers that the corresponding value of C LL T before the recent Belle result was C LL T ∼ 0.35 [20,33] which was strongly disfavoured both by the LHC p p → τ ν searches [26,34,35] the m b scale) shown on the right panel is interesting because it is generated by a single S 1 (3, 1, 1/3) Leptoquark mediator [37]. The allowed range of the WC in this case is [0.113, 0.170] which, as can be seen from Fig.…”

“…The pre-Moriond experimental averages for RD and RD * are based on [9, 10, 13-19].The most general effective Lagrangian for the decay b → c τ −ν τ involving mass dimension-6 operators and only left-chiral neutrinos can be written asc. If one uses power-counting rules arising from linearlyrealised SU(2) × U(1) gauge invariance, it turns out that the Wilson Coefficient (WC) C RL V , with the possibility of lepton non-universality, is only generated at the mass dimension-8 level [20]. Thus, it is expected to be suppressed compared to the other WCs as long as the scale * bardhan@post.bgu.ac.il † diptimoy.ghosh@iiserpune.ac.in of NP is not too close to the Higgs vacuum expectation value, thus we will ignore it in this analysis.…”

Review of lepton universality tests in B decays

“…22. More elaborate scenarios may include several of the above contributions [152]. As indicated before, these analyses depend significantly on the hadronic uncertainties coming from the form factors, with a rather satisfying situation for B → D ν transitions, but not so much for B → D * ν (and also for B − c → J/ψ ν, even though the theoretical predictions Refs.…”

$$b \rightarrow c \tau \nu _{\tau }$$ b → c τ ν τ Decays: a catalogue to compare, constrain, and correlate new physics effects

“…The other model-independent analyses, which are relatively new, can be seen in Refs. [14][15][16][17][18][19][20][21][22]. There are a few other observables, which could be constructed from the B → D ( * ) τ ν τ decays and which are potentially sensitive to the new physics (NP) beyond the SM.…”