Constraining the minimal flavor violating leptoquark explanation of the RD(*) anomaly

Abstract

There has been persistent disagreement between the Standard Model (SM) prediction and experimental measurements of R D ( * ) = B(B → D ( * ) τντ )/B(B → D ( * ) lν l ) (l = e, µ). This anomaly may be addressed by introducing interactions beyond the Standard Model involving new states, such as leptoquarks. Since the processes involved are quark flavor changing, any new states would need to couple to at least two different generations of quarks, requiring a non-trivial flavor structure in the quark sector while avoiding stringent constraints from flavor-changing neutral current processes. In this work, we look at scalar leptoquarks as a possible solution for the R D ( * ) anomaly under the assumption of minimal flavor violation (MFV). We investigate all possible representations for the leptoquarks under the SM quark flavor symmetry group, consistent with asymptotic freedom. We consider constraints on their parameter space from self-consistency of the MFV scenario, perturbativity, the FCNC decay b → sνν and precision electroweak observables. We find that none of the scalar leptoquarks can explain the R D ( * ) anomaly while simultaneously avoiding all constraints within this scenario. Thus scalar leptoquarks with MFV-generated quark couplings do not work as a solution to the R D ( * ) anomaly.

Flavor anomalies from asymptotically safe gravity

“…We move on to the second group of flavor anomalies receiving widespread attention in recent years: the deviations from the SM in the R D ( * ) = BR(B → D ( * ) τ ν)/BR(B → D ( * ) lν) ratios, which have been observed at BELLE and LHCb [57][58][59][60][61][62][63][64], confirming previous hints from BaBar [55,56]. These anomalies in b → c transitions also imply a potential violation of lepton-flavor universality and admit an explanation with LQs [65,96,98,101,[109][110][111][112][113][114][115][116][117][118][119].…”

R2 as a single leptoquark solution to RD(*Попов1, Schmidt2, White3 2019Phys. Rev. D691430View full textAdd to dashboardCite

“…[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] for a leptoquark solution to the R K ðÃÞ anomalies, Refs. [34,[39][40][41][42][43][44][45] for the R D ðÃÞ anomalies and Refs. [34, for simultaneous explanations).…”

Constraints on charmphilic solutions to the muon g−2 with leptoquarks

“…The presence of leptoquarks can modify the coupling Z → ff and induce effects that can be picked up in data from the Z line shape and asymmetry observables. The analytical form of the corresponding loop contribution can be found, for example, in [77]. Since, in the charmphilic assumption, the leptoquark couples only to the second generation of fermions, a loop correction to the effective Z → ff coupling scales proportionally to the Z boson threshold, ∼ |Y R,L 2 | 2 m 2 Z /m 2 S 1 ,R 2 .…”