Narrow Results

The rare t-quark decays , 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 and the total width of the neutrino mode are found. The corresponding branching ratios are shown to be

Fermionic decays of the scalar leptoquarks , , S_m and of the scalar gluons F=F₁, F₂ 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 analyzed in dependence on coupling constants and on masses of the decaying particles. It is shown that the decays , , , , are dominant with the widths of order of a few GeV for m_S, m_F< 1 TeV and with the total branching ratios close to 1. In the case of m_S<m_t the dominant scalar leptoquark decays are , , , with the total branching ratios , and . A search for such decays at the LHC and Tevatron may be of interest.

The contributions of scalar and gauge leptoquarks into widths of , B⁰→e^∓τ^± decays are calculated in the models with the vectorlike and chiral four-color symmetry and with the Higgs mechanism of the quark–lepton mass splitting. From the current data on and B⁰ decays the mass limits for scalar and chiral leptoquarks and the updated vector leptoquark mass limits are obtained. It is shown that unlike the gauge leptoquarks the scalar leptoquark mass limits are weak, of order or below their direct mass limits. The search for such scalar leptoquarks at LHC and the further search for leptonic decays are of interest.

Cross sections of the colored scalar particle production in pp-collisions are calculated and differential and total cross sections of the corresponding parton subprocesses are obtained. The total cross section of scalar gluon production in pp-collisions at the LHC is estimated and the dominant decays of scalar gluons are discussed. The production cross section of scalar gluons F with masses m_F ≲ 1300 GeV is shown to be sufficient for the effective production of these particles at the LHC.

The cross section of the μ⁺μ^- pair production in pp-collisions at the LHC is calculated with account of the Z' boson induced by the minimal four-color quark–lepton symmetry (MQLS). The μ⁺μ^- invariant mass spectrum with account of the MQLS Z' boson is analyzed in dependence on the Z' mass. The mass region for the MQLS Z' boson observable at the LHC is found in dependence on the significance and on the integrated luminosity.

The scalar color octet contribution to the resonance $t\bar{t}$-pair production at the LHC is calculated and analyzed by taking into account the one-loop effective two-gluon vertex. It is shown that this contribution from the scalar color octet $F_2$ predicted by the minimal model with the four-color quark–lepton symmetry is for $\sqrt{s}$ = 13 TeV of about a few percent for 750 $<m_{F_2}<$ 1800 GeV and can exceed 10% for 400 $<m_{F_2}<$ 750 GeV. It is also pointed out that the search for the scalar octet $F_2$ as the resonance in the dijet mass spectra seems to be difficult because of the smallness of its one-loop effective two-gluon interaction.

The contributions of the vector leptoquarks of Pati–Salam type to the branching ratios of $K_L^0,B^0,B_s\to l{l}^{\prime }$ decays are calculated with account of the fermion mixing in the leptoquark currents of the general type. Using the general parametrizations of the mixing matrices the lower vector leptoquark mass limit $m_V$$>$ 86 TeV is found from the current experimental data on these decays. The branching ratios of the decays $B^0,B_s\to l{l}^{\prime }$ predicted at $m_V$ = 86 TeV are calculated. These branching ratios for the decays $B^0,B_s\to {\mu }^{+}{\mu }^{-},e\mu$ are close to the experimental data whereas those for the decays $B^0\to e^{+}{e}^{-},e\tau ,\mu \tau$ and $B_s\to e^{+}{e}^{-}$ are by order of 2–4 less than their current experimental limits. For the decays $B_s\to e\tau ,\mu \tau$ these branching ratios are of orders $10^{-10}$ and $10^{-9}$, respectively. The predicted branching ratios will be useful in the current and future experimental searches for these decays.

The contributions of the chiral gauge leptoquarks $V^{L,R}$ induced by the chiral four-color quark–lepton symmetry to the branching ratios of $K_L^0,B^0,B_s\to l_1{l}_2$ decays are calculated and analyzed using the general parametrizations of the fermion mixing matrices in the leptoquark currents. From the current experimental data on these decays under assumption $m_{V^L}\ll m_{V^R}$, the lower mass limit $m_{V^L}cos{\gamma }_L>5.68\mathrm{\text{TeV}}$ is found, which in particular case of equal gauge coupling constants gives $m_{V^L}>8.03\mathrm{\text{TeV}}$. The branching ratios of the decays under consideration predicted by the chiral gauge leptoquarks are calculated and analyzed in dependence on the leptoquark masses and the mixing parameters. It has shown that in consistency with the current experimental data, these branching ratios for $B_s,B^0\to \mu e$ decays can be close to their experimental limits and those for $B_s,B^0\to \tau e,\tau \mu$ decays can be of order of $10^{-7}$. The calculated branching ratios will be useful in the further experimental searches for these decays.