The role of the S 3 GUT leptoquark in flavor universality and collider searches

Abstract

Abstract:We investigate the ability of the S 3 scalar leptoquark to address the recent hints of lepton universality violation in B meson decays. The S 3 leptoquark with quantum numbers (3, 3, 1/3) naturally emerges in the context of an SU(5) GUT model without any conflict with the stringent limits from observed nucleon stability. Scalar leptoquark S 3 with left-handed couplings to 2nd and 3rd generations of charged leptons and down-type quarks seems well-suited to address both R K ( * ) and R D ( * ) . We quantify this suitability with numerical fits to a plethora of relevant flavor observables. The proposed SU(5) model calls for a second leptoquark state, i.e.,R 2 with quantum numbers (3, 2, 1/6), if one is to generate gauge coupling unification and neutrino mass. We accordingly include it in our study to investigateR 2 's ability to offset adverse effects of S 3 and thus improve a quality of numerical fits. A global fit of the leptoquark Yukawa couplings shows that large couplings of light S 3 to τ leptons are preferred. We furthermore identify B → K ( * )ν ν as the most sensitive channel to probe the preferred region of parameter space. Large couplings of S 3 to τ leptons are finally confronted with the experimental searches for τ final states at the Large Hadron Collider. These searches comprise a study of decay products of the leptoquark pair production, as well as, and more importantly, an analysis of the high-mass τ τ final states.

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].…”

Footprints of leptoquarks: from $$ R_{K^{(*)}} $$ R K ( ∗ ) to

“…However, it was found in a full-fledged model, matched onto the effective Lagrangian, that it is very difficult to accommodate within 1σ the large value of R D ( * ) [24]. On the other hand it seems that R K ( * ) can be explained by a number of leptoquarks which contribute to b → sμ + μ − transition either at the tree-level [22,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] or at the loop-level [40][41][42].…”

“…According to the classification in [48], scalar leptoquarks which are doublets of SU (2) L cannot destabilize the proton via the diquark coupling, since 3B + L = 0, B and L being baryon and lepton numbers, 4 and therefore can be relatively light. Moreover, it was pointed out in [24,55] that the weak triplet leptoquark, although having 3B + L = 2, when embedded in a SU (5) GUT model does not destabilize the proton. The weak doublet leptoquarks may have weak hypercharges 7/6 or 1/6.…”

“…In Ref. [24] an attempt was done to explain all B-meson anomalies in this GUT setup, accounting for all the existing low-energy constraints. As already noticed by the authors of [34,47] the current bounds on R ( * ) νν are rather restrictive for the leptoquark models and since S 3 andR 2 contribute to B → K ( * ) νν at tree-level they cannot fully accommodate the R D ( * ) anomaly.…”

“…In Refs. [24,55], a model with two LQs has been considered, namely S 3 = (3, 3, 1/3) and R 2 = (3, 2, 1/6). The authors of that model noticed that these two leptoquark states are important for the one-loop neutrino mass mechanism within the framework of grand unification theory (GUT) [24,55].…”