7 research outputs found

    Neutrino charge radius and electromagnetic dipole moments via scalar and vector leptoquarks

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    The one-loop contribution of scalar and vector leptoquarks (LQs) to the electromagnetic properties (NEPs) of massive Dirac neutrinos is presented via an effective Lagrangian approach, with emphasis on the effective neutrino charge radius (NCR), which has never been calculated and is obtained by the background field formalism in a Yang-Mills-like scenario for gauge LQs. Analytical results for nonzero neutrino mass are presented in terms of both Feynman-parameter integrals and Passarino-Veltman scalar functions, which can be useful to obtain the NEPs of heavy neutrinos, out of which approximate expressions are obtained for light neutrinos. For the numerical analysis we concentrate on the only renormalizable scalar and vector LQ representations that do not need extra symmetries to forbid tree-level proton decay. Constraints on the parameter space consistent with current experimental data are then discussed and it is found that the LQ representations R~2\widetilde{R}_2 and U1U_1 could yield the largest contributions to the NEPs provided that they have couplings to both left- and right-handed neutrinos of the order of O(1)O(1). For a LQ mass of 1.51.5 TeV, the magnetic dipole moment (MDM) of the tau neutrino can be of the order of 10−910^{-9} ÎŒB\mu_B, whereas its neutrino electric dipole moment (EDM) can reach values as high as 10−2010^{-20}-10−1910^{-19} ecm. On the other hand, the NCR can reach values up to 10−3510^{-35} cm2^2 regardless of the neutrino flavor and even in the absence of right-handed neutrinos. In the latter scenario, the EDM vanishes and the contribution to neutrino MDM would be negligible, of the order of 10−1410^{-14} ÎŒB\mu_B for the tau neutrino, whereas those for the muon and electron neutrinos would be about two and seven orders of magnitude smaller, respectively. Our estimates could be severely suppressed due to a possible suppression of the LQ coupling constants.Comment: 31 pages, 11 figure

    Rare decay t→cγγt\to c\gamma\gamma via scalar leptoquark doublets

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    A calculation of the one-loop contribution to the rare three-body flavor changing neutral current top quark decay t→cγγt\to c\gamma\gamma is presented in the framework of models with one or more scalar leptoquark SU(2)SU(2) doublets with hypercharge 7/67/6. Analytical expressions for the invariant amplitude of the generic decay fi→fjγγf_i\to f_j\gamma\gamma, with fi,jf_{i,j} a lepton or quark, are presented in terms of Passarino-Veltman integral coefficients, from which the amplitudes for the processes t→cγγt\to c\gamma\gamma and ℓi→ℓjγγ\ell_i\to \ell_j\gamma\gamma follow easily. An analysis of the current constraints on the parameter space is presented in the scenario with only one scalar LQ doublet and bounds on the LQ couplings are obtained from the muon g−2g-2 anomaly, the lepton flavor violating (LFV) decay Ï„â†’ÎŒÎł\tau\to \mu\gamma and extra constraints meant to avoid tension between theory predictions and experimental data. For a LQ with a mass in the range of 11--1.51.5 TeVs, the estimate Br(t→cγγ)∌10−11{\rm Br}(t\to c\gamma\gamma)\sim 10^{-11}--10−1210^{-12} is obtained for the largest allowed values of the LQ coupling constants, which means that this decay would be below the reach of future experimental measurements. We also consider an scenario with three scalar doublets, which was recently proposed to explain the lepton flavor universality violation anomalies in BB decays as well as the muon g−2g-2 anomaly. Although this scenario allows large LQ couplings to the tau lepton and the cc and tt quarks, the branching ratio of the t→cγγt\to c\gamma\gamma decay is also of the order of 10−1110^{-11}--10−1210^{-12} for LQ masses of 1.7 TeV.Comment: In preparation for Journal Submissio

    Minimal spontaneously broken hidden sector and its impact on Higgs boson physics at the Large Hadron Collider

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    We have studied a hidden sector of the SM with spontaneous symmetry breaking that opens many different scenarios for Higgs physics. We have shown that this hidden sector can affect the SM Higgs detection. In some speci c regimes it is still possible to detect the Higgs; in other scenarios the hidden sector would completely eclipse it

    Neutrino charge radius and electromagnetic dipole moments via scalar and vector leptoquarks

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    The one-loop contribution of scalar and vector leptoquarks (LQs) to the electromagnetic properties (NEPs) of massive Dirac neutrinos is presented via an effective Lagrangian approach. For the contribution of gauge LQs to the effective neutrino charge radius defined in Bernabeu et al. (Phys Rev Lett 89:101802, 2002. https://doi.org/10.1103/PhysRevLett.89.10180
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