A hypothetical particle that can turn a quark into a lepton and vice versa. Leptoquarks can either be scalar (spin-0) bosons or vector (spin-1) bosons. They can be as heavy as lead atoms and are predicted to decay very rapidly into quarks and leptons. It is natural for leptoquarks to exist in many theories that go beyond the standard model, notably grand unified theories. Although leptoquarks have not been detected, their existence has been used to explain some results from the Large Hadron Collider that do not appear to be in accord with the standard model.