Simultaneous explanation of R(D (∗)) and b→sμ + μ −: the last scalar leptoquarks standing

Abstract

Over the past years, experiments accumulated intriguing hints for new physics (NP) in flavor observables, namely in the anomalous magnetic moment of the muon (a µ ), in R(D ( * ) ) = Br(B → D ( * ) τ ν)/Br(B → D ( * ) ν) and in b → sµ + µ − transitions, which are all at the 3 − 4 σ level. In this article we point out that one can explain the R(D ( * ) ) anomaly using two scalar leptoquarks (LQs) with the same mass and coupling to fermions related via a discrete symmetry: an SU(2) L singlet and an SU(2) L triplet, both with hypercharge Y = −2/3. In this way, potentially dangerous contributions to b → sνν are avoided and non-CKM suppressed effects in R(D ( * ) ) can be generated. This allows for smaller overall couplings to fermions weakening the direct LHC bounds. In our model, R(D ( * ) ) is directly correlated to b → sτ + τ − transitions where an enhancement by orders of magnitude compared to the standard model (SM) is predicted, such that these decay modes are in the reach of LHCb and BELLE II. Furthermore, one can also naturally explain the b → sµ + µ − anomalies (including R(K)) by a C 9 = −C 10 like contribution without spoiling µ − e universality in charged current decays. In this case sizable effects in b → sτ µ transitions are predicted which are again well within the experimental reach. One can even address the longstanding anomaly in a µ , generating a sizable decay rate for τ → µγ. However, we find that out of the three anomalies R(D ( * ) ), b → sµ + µ − and a µ only two (but any two) can be explained simultaneously. We point out that a very similar phenomenology can be achieved using a vector leptoquark SU(2) L singlet with hypercharge 2/3. In this case, no tuning between couplings is necessary, but the model is non-renormalizable.

Lepton polarization asymmetries in rare semi-tauonic $$ b \rightarrow s $$ b → s exclusive decays at FCC-ee

“…In the present analysis, we do not discuss possible UV completions of H eff but instead refer the interested reader to the existing literature on the subject [24,[63][64][65].…”

RK and RK* beyond the standard model

“…Applied to leptoquark models this allows to select lepton speciesfor instance having only couplings to one lepton species, muons, or electrons [16]. Corrections to lepton isolation arise from rotations to the mass basis and at higher order in the spurion expansion, and induce lepton flavor violation [12,16,[27][28][29][30] such as B → Kµτ , which can be probed with B-physics experiments but also µ − econverison, rare K and → decays. Together with B → K ( * ) νν modes the latter constitute the leading constraints on flavor models and LNU anomalies, and improved experimental study is promising.…”

B Meson Anomalies in a Pati-Salam Model within the Randall-Sundrum Background

“…Furthermore, also RðJ=ΨÞ points towards the violation of LFU in b → cτν processes [10]. This suggests a possible connection between these two classes of decays and motivates the investigation of simultaneous explanations [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].…”

“…It contributes to b → sμ þ μ − as well as to b → cτν, and it does not couple down quarks to neutrinos, avoiding the bounds from B → K ðÃÞ νν and is free of proton decay to all orders in perturbation theory [31]. This allows for large flavor violating effects and the bounds from direct searches [32], and electroweak (EW) precision data [33,34] can be avoided [24,27]. Interestingly, this LQ appears in the theoretically very appealing Pati-Salam (PS) [35] model, and several attempts have been made in the literature to construct a model addressing the flavor anomalies based on the corresponding gauge symmetry [28][29][30]36].…”