Same-sign single dilepton productions at the LHC

We examine the same-sign single dilepton productions of $\ell_i^{\pm}\ell_j^{\pm} (\ell_{i,j}=e,\mu)$ in high-energy proton-proton collisions at the Large Hadron Collider (LHC) in models with doubly charged Higgs scalars as well as heavy Majorana neutrinos. We demonstrate that these spectacular productions can be detected at the LHC for a class model in which the doubly charged Higgs scalars couple only to the right-handed charged leptons. The ranges of the possible doubly charged Higgs masses and mixings to observe the processes at the LHC are discussed.Comment: 10 pages, 5 figure

An A_5 Model of Four Lepton Generations

We study the lepton sector of a four generations model based on the discrete flavor group $A_5$ (the even permutation of five objects). The best features of the three family $A_4$ model survive, including the tribimaximal pattern of three generation neutrino mixings. At leading order the three light neutrino mass relations of $m_{\nu_1} = m_{\nu_3}$ and $m_{\nu_2} = 0$ are predicted. The splitting of the neutrino masses can be naturally obtained as a result of the breaking of $A_{5}$ down to $A_4$ and a degenerate spectrum is preferred in our model. In our $A_5$ model, the electron mass is zero at tree level, but calculable through quantum corrections.Comment: 20 pages, 3 figures, and 3 tables; references and Appendix C added, version accepted for publication in JHE

Neutrino masses, muon g-2, dark matter, lithium problem, and leptogenesis at TeV-scale

Observational evidences of nonzero neutrino masses and the existence of dark matter request physics beyond standard model. A model with extra scalars and leptonic vector-like fermions is introduced. By imposing a Z_2 symmetry, the neutrino masses as well as anomalous muon magnetic moment can be generated via one-loop effects at TeV-scale. An effort of explaining dark matter, Lithium problem, and leptogenesis is presented. This scenario can be tested at LHC and/or future experiments.Comment: 5 pages, 5 figure

Non-zero U_{e3} and TeV-Leptogenesis through A_4 symmetry breaking

We consider an effective theory with an $SU(2)\times U(1)\times A_{4}\times Z_{2}\times Z_{4}$ symmetry and investigate the possibility of a linking TeV-leptogenesis with a reactor angle $|U_{e3}|$ through spontaneous $A_{4}$ symmetry breaking which is at a scale higher than electroweak scale under the framework of radiative seesaw. It has been shown that tri-bimaximal(TBM) can be obtained by forging vacuum expectation value (VEV) alignment of the $A_{4}$. Especially, one $A_{4}$ triplet scalar field with cut-off scale $\Lambda$ is added in neutrino Yukawa sector, which is responsible for the deviation of the exact TBM, to explain leptogenesis as well as a non-zero $|U_{e3}|$. Above the scale of $\Lambda$ the leptonic Yukawa sectors will lead to the exact TBM. We analyze possible spectrums of light neutrinos and their flavor mixing angles corresponding to heavy Majorana neutrino mass ordering, and show that non-resonance leptogenesis at TeV-scale constrained by low energy data is achievable, both analytically as well as numerically. We show that only normal hierarchical spectrum of light neutrino would be strongly favored by the current Wilkinson Microwave Anisotropy Probe (WMAP) data, and also show that a relatively large $|U_{e3}|$ corresponds to the value of baryon asymmetry $6.2\times10^{-10}$.Comment: 32 pages, 21 figures, 3 tables. Final version to appear in Phys. Rev.

Relating Neutrino Masses by dilepton modes of Doubly Charged Scalars

We study a model with Majorana neutrino masses generated through doubly charged scalars at two-loop level. We give explicit relationships between the neutrino masses and the same sign dilepton decays of the doubly charged scalars. In particular, we demonstrate that at the tribimaximal limit of the neutrino mixings, the absolute neutrino masses and Majorana phases can be extracted through the measurements of the dilepton modes at colliders.Comment: 14 pages, 8 figures, references added, version to be published in PR

Neutrino mass generation and H → γγ/Zγ correlation with scalar multiplets

One natural way to understand the excess of the measured H → γγ rate over the standard model (SM) expectation at the Large Hadron Collider (LHC) is to have charged scalar bosons, existing in most of the SM extensions. Motivated by this LHC result, we explore if it also sheds light on solving the small neutrino mass generation problem. We concentrate on a class of models with high-dimensional representations of scalars to realize Majorana neutrino masses at the two-loop level without imposing any new symmetry. In these models, multi scalars with electric charges higher than two are naturally expected, which not only enhance the H → γγ rate, but provide more searching grounds at the LHC. In particular, the rate of H → Zγ is also correlated to that of the diphoton channel