2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/45279A possible Standard Model extension of the Pati-Salam type with a lepton number as the fourth color is reexamined. A new type of mixing in the interaction of the $SU(4)_V$--leptoquark with quarks and leptons 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 $M_X > 18~TeV$.(talk given at the VIII International Seminar "Quarks-94", Vladimir, Russia, May 11-18, 1994), 7 pages, LaTeX, uses world_sc.sty, Yaroslavl, Yaroslavl State University preprint YARU-HE-94/03High Energy Physics - Phenomenologytext