7 research outputs found
Neutrino charge radius and electromagnetic dipole moments via scalar and vector leptoquarks
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
and could yield the largest contributions to the NEPs
provided that they have couplings to both left- and right-handed neutrinos of
the order of . For a LQ mass of TeV, the magnetic dipole moment
(MDM) of the tau neutrino can be of the order of , whereas its
neutrino electric dipole moment (EDM) can reach values as high as
- ecm. On the other hand, the NCR can reach values up to
cm 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
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 via scalar leptoquark doublets
A calculation of the one-loop contribution to the rare three-body flavor
changing neutral current top quark decay is presented in
the framework of models with one or more scalar leptoquark doublets
with hypercharge . Analytical expressions for the invariant amplitude of
the generic decay , with a lepton or quark,
are presented in terms of Passarino-Veltman integral coefficients, from which
the amplitudes for the processes and 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
anomaly, the lepton flavor violating (LFV) decay and extra
constraints meant to avoid tension between theory predictions and experimental
data. For a LQ with a mass in the range of -- TeVs, the estimate -- 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 decays as well as the
muon anomaly. Although this scenario allows large LQ couplings to the tau
lepton and the and quarks, the branching ratio of the decay is also of the order of -- 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
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
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