Limits on scalar leptoquark interactions and consequences for GUTs

TL;DR

This paper explores the constraints on a specific scalar leptoquark's interactions, analyzing its effects on flavor physics and GUT models, and finds that certain grand unified theories are incompatible with the observed data.

Contribution

It provides a comprehensive global fit of scalar leptoquark couplings, linking flavor observables with grand unified theories and identifying model incompatibilities.

Findings

The scalar leptoquark can explain the muon g-2 anomaly.

SU(5) GUT models are incompatible with the fit.

SO(10) models require additional representations for viability.

Abstract

A colored weak singlet scalar state with hypercharge 4/3 is one of the possible candidates for the explanation of the unexpectedly large forward-backward asymmetry in t tbar production as measured by the CDF and D0 experiments. We investigate the role of this state in a plethora of flavor changing neutral current processes and precision observables of down-quarks and charged leptons. Our analysis includes tree- and loop-level mediated observables in the K and B systems, the charged lepton sector, as well as the Z to b bbar decay width. We perform a global fit of the relevant scalar couplings. This approach can explain the (g-2)_mu anomaly while tensions among the CP violating observables in the quark sector, most notably the nonstandard CP phase (and width difference) in the Bs system cannot be fully relaxed. The results are interpreted in a class of grand unified models which allow for a light colored scalar with a mass below 1TeV. We find that the renormalizable SU(5) scenario is not compatible with our global fit, while in the SO(10) case the viability requires the presence of both the 126- and 120-dimensional representations.