Pati-Salam and lepton universality in B decays

TL;DR

This paper explores how scalar leptoquarks, predicted by the Pati-Salam grand unified theory, can explain recent anomalies in B-meson decays and predict observable lepton flavor violation and other phenomena.

Contribution

It demonstrates that GUT-motivated scalar leptoquarks naturally emerge in the Pati-Salam model and connect B-decay anomalies with neutrino mass mechanisms and testable predictions.

Findings

Leptoquarks can explain R(K^{(*)}) anomalies linked to neutrino mass matrices.

Light right-handed neutrinos are needed to explain R(D^{(*)}) anomalies.

Predictions include lepton flavor violation signals at LHC and other B-decay channels.

Abstract

Recent hints for lepton-flavor non-universality in $B$-meson decays can be interpreted as hints for the existence of leptoquarks. We show that scalar leptoquarks unavoidably arise in grand unified theories, using the well-known Pati-Salam model as an example. These GUT-motivated leptoquarks can have a number of appealing features including automatic absence of proton decay, purely chiral couplings, and relations between the various leptoquark couplings. We show that $R(K^{(*)})$ can be connected to the neutrino mass matrix that arises via type-II seesaw, resulting in testable lepton flavor violation. In order to also explain $R(D^{(*)})$ one instead has to assume the existence of light right-handed neutrinos, once again with testable predictions in other $B$-meson decays and at the LHC.