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

Abstract

We investigate the ability of the S3 scalar leptoquark to address the recent hints of lepton universality violation in B meson decays. The S3 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 S3 with left-handed couplings to 2nd and 3rd generations of charged leptons and down-type quarks seems well-suited to address both RK(∗) and RD(∗). 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 investigate R˜ 2’s ability to offset adverse effects of S3 and thus improve a quality of numerical fits. A global fit of the leptoquark Yukawa couplings shows that large couplings of light S3 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 S3 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 ττ finalstates.