Radiative Neutrino Mass Models

In this short review, we see some typical models in which light neutrino masses are generated at the loop level. These models involve new Higgs bosons whose Yukawa interactions with leptons are constrained by the neutrino oscillation data. Predictions about flavor structures of $ell to overline{ell}_1 ell_2 ell_3$ and leptonic decays of new Higgs bosons via the constrained Yukawa interactions are briefly summarized in order to utilize such Higgs as a probe of $ u$ physics.

Discrimination of Models Including Doubly Charged Scalar Bosons by Using Tau Lepton Decay Distributions

The doubly-charged scalar boson H^{--} is involved in several new physics models for generating neutrino masses. Depending on new physics models, H^{--} has the Yukawa interaction with a pair of left-handed charged leptons or a pair of right-handed ones. In this talk, we see that these two Yukawa interactions can be distinguished by measuring energy distributions of charged pions produced by decays of tau leptons if pair-produced H^{++} H^{--} can decay sufficiently into four charged leptons which involve one or two tau leptons. The information on the Yukawa interaction of H^{--} will help to discriminate models in which neutrino masses are generated.

Dependence of the leptonic decays of H^- on the neutrino mixing angles theta_{13} and theta_{23} in models with neutrinophilic charged scalars

In the Higgs Triplet Model and the neutrinophilic Two-Higgs-Doublet Model the observed neutrinos obtain mass from a vacuum expectation value which is much smaller than the vacuum expectation value of the Higgs boson in the Standard Model. Both models contain a singly charged Higgs boson (H^-) whose Yukawa coupling is directly related to the neutrino mass (i.e. a neutrinophilic charged Higgs). The partial decay widths of H^- into a charged lepton and a neutrino (H^- to l^- nu) depend identically on the neutrino masses and mixings in the two models. We quantify the impact of the recent measurement of sin^2(2theta_{13}), which plays a crucial role in determining the magnitude of the branching ratio of H^- to e^- nu for the case of a normal neutrino mass ordering if the lightest neutrino mass m_0 < 10^{-3} eV. We also discuss the sizeable dependence of H^- to mu^- nu and H^- to tau^- nu on sin^2(theta_{23}), which would enable information to be obtained on sin^2(theta_{23}) and the sign of Delta m^2_{31} if these decays are measured. Such information would help neutrino oscillation experiments to determine the CP-violating phase delta.

Neutrino Mass in TeV-Scale New Physics Models

This is a short review about relations between new scalars and mechanisms to generate neutrino masses. We investigate leptohilic scalars whose Yukawa interactions are only with leptons. We discuss possibilities that measurements of their leptonic decays provide information on how neutrino masses are generated and on parameters in the neutrino mass matrix (e.g. the lightest neutrino mass).

Lepton number violation at the LHC with leptoquark and diquark

We investigate a model in which tiny neutrino masses are generated at the two-loop level by using scalar leptoquark and diquark multiplets. The diquark can be singly produced at the LHC, and it can decay into a pair of leptoquarks through the lepton number violating interaction. Subsequent decays of the two leptoquarks can provide a clear signature of the lepton number violation, namely two QCD jets and a pair of same-signed charged leptons without missing energy. We show that the signal process is not suppressed while neutrino masses are appropriately suppressed.

Discrimination of models including doubly charged scalar bosons by using tau lepton decay distributions

The doubly charged scalar boson (H^{pmpm}) is introduced in several models of the new physics beyond the standard model. The H^{pmpm} has Yukawa interactions with two left-handed charged leptons or two right-handed charged leptons depending on the models. We study kinematical properties of H^{pmpm} decay products through tau leptons in order to discriminate the chiral structures of the new Yukawa interaction. The chirality of tau leptons can be measured by the energy distributions of the tau decay products, and thus the chiral structure of the new Yukawa interaction can be traced in the invariant-mass distributions of the H^{pmpm} decay products. We perform simulation studies for the typical decay patterns of the H^{pmpm} with simple event selections and tau-tagging procedures, and show that the chiral structure of the Yukawa interactions of H^{pmpm} can be distinguished by measuring the invariant-mass distributions.