Fermionic decays of the scalar leptoquarks S = S (+) 1 , S (−) 1 , S m and of the scalar gluons F = F 1 , F 2 predicted by the four color symmetry model with the Higgs mechanism of the quark-lepton mass splitting are investigated. Widths and branching ratios of these decays are calculated and analysed in dependence on coupling constants and on masses of the decaying particles. It is shown that the decays S One of the goals of the forthcoming experiments at LHC (in addition to the search for the Higgs boson and to the further studies of the Standard Model (SM)) will be the search for the possible effects of the new physics beyond the SM. There is a lot of the variants of new physics beyond the SM predicting new effects at energies of LHC (supersymmetry, left -right symmetry, two Higgs model, etc.).One of such variants can be the variant induced by the possible four color symmetry between quarks and leptons of Pati-Salam type [1]. The immediate consequence of this symmetry is the prediction of the gauge leptoquarks which, however, occur to be relatively heavy (for example, the resulted from the unobservation of the K 0 L → µ ± e ∓ decays the most stringent lower mass limit for the vector leptoquarks is of order of 10 3 TeV). By this reason it is usually thought that the effects of the four color symmetry at the colliders energies are too small to be directly detectable in the collider experiments of the near future. * E-mail: popov p@univ.uniyar.ac.ru † E-mail: povarov@univ.uniyar.ac.ru ‡ E-mail: asmirnov@univ.uniyar.ac.ru 1 It should be noted however that in addition to the gauge leptoquarks the four color symmetry can predict also the new scalar particles. Thus, in the case of the Higgs mechanism of splitting the masses of quarks and leptons the four color symmetry in its minimal realization on the gauge group(MQLS-model [2,3]) needs the existence of the scalar particles belonging to the (15,2,1) -multiplet of the group G. This multiplet contains fifteen scalar SU L (2)-doublets: two scalar leptoquark doublets S (±) , scalar gluon doublet F and a SU c (3)-colorless scalar doublet which in admixture with the (1, 2, 1) -doublet forms the SM Higgs doublet Φ (SM ) and an additional colorless scalar doublet Φ ′ . All these scalar doublets are necessary [4] for splitting the the masses of quarks from those of leptons by the Higgs mechanism and for generating the quark -lepton mass splittings including the so large mass splittings as the b − τ and t − ν τ ones.Because of their Higgs origin the coupling constants of these scalar doublets with the fermions are proportional to the ratios m f /η of the fermion masses m f to the SM VEV η. The effects of these scalar leptoquarks in the processes with the ordinary u-, d-, s-quarks are small because of the smallness of the corresponding coupling constants(but these effects can be significant in c-, b-and, especially, in top-physics m c /η ∼ m b /η ∼ 10 −2 , m t /η ∼ 0.7). As a result the scalar leptoquark doublets S (±) and the scalar gluon doublet F can be relative...

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The rare t-quark decays [Formula: see text], [Formula: see text] via the scalar leptoquark doublets are investigated in the minimal four-color symmetry model with the Higgs mechanism of the quark–lepton mass splitting. The partial widths of these decays are calculated and the total width of the charged lepton mode [Formula: see text] and the total width of the neutrino mode [Formula: see text] are found. The corresponding branching ratios are shown to be [Formula: see text] for the scalar leptoquark masses mS = 180–250 GeV and for the appropriate values (sin β≈ 0.2) of the mixing angle of the model. The search for such decays at LHC may be of interest.