Vector Leptoquarks Could Be Rather Light?

Abstract

Some low-energy manifestations of a minimal extension of the Standard Model based on the quark-lepton $SU(4)_V \otimes SU(2)_L \otimes G_R$ symmetry of the Pati-Salam type are analysed. Given this symmetry a new type of mixing in the quark-lepton interactions is shown to be required. An additional arbitrariness of the mixing parameters could allow to decrease noticeably the lower bound on the leptoquark mass $M_X$ originated from the $π$ and $K$ decays and the $μe$ conversion. The only mixing independent bound emerging from the cosmological limit on the $π^0 \rightarrow ν\barν$ decay width is $M_X > 18~TeV$.