The measurement of R D (R D * ), the ratio of the branching fraction of B → Dτν τ (B → D * τν τ ) to that of B → Dlν l (B → D * lν l ), shows 1.9σ (3.3σ) deviation from its Standard Model (SM) prediction. The combined deviation is at the level of 4σ according to the Heavy Flavour Averaging Group (HFAG). In this paper, we perform an effective field theory analysis (at the dimension 6 level) of these potential New Physics (NP) signals assuming SU(3) C × SU(2) L × U(1) Y gauge invariance. We first show that, in general, R D and R D * are theoretically independent observables and hence, their theoretical predictions are not correlated. We identify the operators that can explain the experimental measurements of R D and R D * individually and also together. Motivated by the recent measurement of the τ polarisation in B → D * τν τ decay, P τ (D * ) by the Belle collaboration, we study the impact of a more precise measurement of P τ (D * ) (and a measurement of P τ (D)) on the various possible NP explanations. Furthermore, we show that the measurement of R D * in bins of q 2 , the square of the invariant mass of the lepton-neutrino system, along with the information on τ polarisation and the forward-backward asymmetry of the τ lepton, can completely distinguish the various operator structures. We also provide the full expressions of the double differential decay widths for the individual τ helicities in the presence of all the 10 dimension-6 operators that can contribute to these decays.
A 125 GeV Higgs renders the simpler GMSB models unnatural, essentially pushing the soft spectrum beyond the LHC reach. A direct coupling of the matter and messenger fields, that facilitates an enhanced mixing in the squark sector, is a way to ameliorate this deficiency. We construct all possible messenger-matter interaction terms considering the messenger multiplets in 1, 5 and 10 dimensional representations of the SU(5). A Froggatt-Nielsen like flavor framework connected with the origin of fermion mass hierarchy is utilized to control the interaction terms and suppress FCNC. We perform a detailed comparative study of the efficiency of such interaction terms to boost the Higgs mass keeping the soft spectrum light. We identify the more promising models and comment on their status in present and future collider studies.
The recent LHCb measurement of RK * in two q 2 bins, when combined with the earlier measurement of RK , strongly suggests lepton flavour non-universal new physics in semi-leptonic B meson decays. Motivated by these intriguing hints of new physics, several authors have considered vector, axial vector, scalar and pseudo scalar operators as possible explanations of these measurements. However, tensor operators have widely been neglected in this context. In this paper, we consider the effect of tensor operators in RK and RK * . We find that, unlike other local operators, tensor operators can comfortably produce both of R low K * and R central K * close to their experimental central values. However, a simultaneous explanation of RK is not possible with only Tensor operators, and other vector or axial vector operators are needed. In fact, we find that combination of vector and tensor operators can provide simultaneous explanations of all the anomalies comfortably at the 1σ level, a scenario which is hard to achieve with only vector or axial vector operators. We also comment on the compatibility of the various new physics solutions with the measurements of the inclusive decay B d → Xs + − .
Abstract:We look for minimal extensions of Standard Model with vector like fermions leading to precision unification of gauge couplings. Constraints from proton decay, Higgs stability and perturbativity are considered. The simplest models contain several copies of vector fermions in two different (incomplete) representations. Some of these models encompass Type III seesaw mechanism for neutrino masses whereas some others have a dark matter candidate. In all the models, at least one of the candidates has non-trivial representation under SU(3) color . In the limit of vanishing Yukawa couplings, new QCD bound states are formed, which can be probed at LHC. The present limits based on results from 13 TeV already probe these particles for masses around a TeV. Similar models can be constructed with three or four vector representations, examples of which are presented.
The gauged U (1)L µ−Lτ model can provide for additional contributions to the muon anomalous magnetic moment by means of a loop involving the Z gauge boson. However, the parameter space of such models is severely constrained if one combines the latest muon (g − 2) data with various neutrino experiments, such as neutrino trident production, ν − e and ν − q elastic scattering, etc. In a supersymmetric U (1)L µ−Lτ model, a larger region of parameter space opens up, thus enabling one to explore otherwise forbidden regions of parameter space in nonsupersymmetric models involving the new gauge coupling (gX ) and the mass of the Z gauge boson (M Z ) . We show that the minimal model with the minimal supersymmetric Standard Model (MSSM) field content is strongly disfavored from Z-boson decay and neutrino data. We also show that the nonminimal model with two extra singlet superfields can lead to correct neutrino masses and mixing involving both tree-level and one-loop contributions. We find that, in this model, both muon (g − 2) and neutrino data may be simultaneously explained in a parameter region consistent with experimental observations. In addition, we observe that the muon (g − 2) anomaly can be accommodated even with higher values of electroweak sparticle masses compared to the MSSM. Charged lepton-flavorviolating processes (like µ → eγ, τ → µγ, etc.) may have potentially large branching ratios in this scenario. Depending on the magnitude of the supersymmetry contribution to these processes, they may constrain hitherto unconstrained regions of the M Z − gX parameter space. However, we find that these branching fractions never exceed their upper bounds in a region where both muon (g − 2) and neutrino oscillation data can be simultaneously accommodated. arXiv:1805.04415v2 [hep-ph] 5 Nov 2018 c eLµÊ c µLτÊ c τĤuĤd U (1)L µ−Lτ 0 0 0 0 0 1 -1 -1 1 0 0
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.