Leptonquark

Leptonquark, a term sometimes used to describe a leptoquark, is a hypothetical boson that couples to both a lepton and a quark. Leptoquarks carry lepton number and baryon number and can be either scalar (spin-0) or vector (spin-1). They arise in several beyond-Standard-Model frameworks, most notably grand unified theories such as SU(5) and SO(10), and in Pati-Salam models that unify quarks and leptons within a common multiplet. They can also appear in composite models in which quarks and leptons are bound states of more fundamental constituents. Leptoquarks are typically color triplets under SU(3) and have various electroweak quantum numbers, which determine their electric charge and weak interactions. Their defining feature is Yukawa-type couplings that connect a lepton to a quark, enabling transitions between the two sectors and potentially contributing to processes that violate lepton flavor universality if couplings differ between generations.

Experiments search for leptoquarks primarily through pair production at colliders, driven by quantum chromodynamics, and through single production proportional to the leptoquark–lepton–quark coupling. If produced, they decay into a lepton and a quark, yielding final states with jets and leptons. Current results from the Large Hadron Collider have not observed a leptoquark, placing lower mass limits on the order of about a TeV to several TeV, depending on the generation and branching ratios. Leptoquarks remain a focus of study because of their potential to address flavor anomalies observed in rare B decays and to reveal new connections between matter particles and fundamental interactions.