Takashi Toma

Lepton Flavor Violation in the Scotogenic Model

A bstractWe investigate lepton flavor violation in the scotogenic model proposed by Ma in which neutrinos acquire non-zero masses at the 1-loop level. Although some works exist in this direction, they have mainly focused on the radiative decay ℓαu2009→u2009ℓβγ. Motivated by the promising new projects involving other low-energy processes, we derive complete analytical expressions for ℓαu2009→u20093 ℓβ and μu2009−u2009e conversion in nuclei, and numerically study their impact on the phenomenology. We will show that these processes can actually have rates larger than the one for ℓαu2009→u2009ℓβγ, thus providing more stringent constraints and better experimental perspectives.

Multicomponent dark matter particles in a two-loop neutrino model

We construct a loop induced seesaw model in a TeV scale theory with gauged U(1)B−L symmetry. Light neutrino masses are generated at two-loop level and right-handed neutrinos also obtain their masses by one-loop effect. Multi-component Dark Matters (DMs) are included in our model due to the remnant discrete symmetry after the B − L symmetry breaking and the Z2 parity which is originally imposed to the model. We investigate the multi-component DM properties, in which we have two fermionic DMs with different mass scales, O(10) GeV and O (100-1000) GeV. The former mass corresponds to the lightest right-handed neutrino mass induced by the loop effect, although the latter one to the SM gauge singlet fermion. We show each of the DM annihilation processes and compare to the observation of relic abundance, together with the constraints of Lepton Flavor Violation (LFV) and active neutrino masses. Moreover we show that our model has some parameter region allowed by the direct detection result reported by XENON100, and it is possible to search the region by the future XENON experiment.

Impact of semi-annihilation of

We investigate a 3 symmetric model with two-loop radiative neutrino masses. Dark matter in the model is either a Dirac fermion or a complex scalar as a result of an unbroken 3 symmetry. In addition to standard annihilation processes, semi-annihilation of the dark matter contributes to the relic density. We study the effect of the semi-annihilation in the model and find that those contributions are important to obtain the observed relic density. The experimental signatures in dark matter searches are also discussed, where some of them are expected to be different from the signatures of dark matter in 2 symmetric models.

\mathbb{Z}_3

Abstract We study an exciting dark matter scenario in a radiative neutrino model to explain the X-ray line signal at 3.55 keV recently reported by XMN-Newton X-ray observatory using data of various galaxy clusters and Andromeda galaxy. We show that the required large cross section for the up-scattering process to explain the X-ray line can be obtained via the resonance of the pseudo-scalar. Moreover, this model can be compatible with the thermal production of dark matter and the constraint from the direct detection experiment.

symmetric dark matter with radiative neutrino masses

We study a two loop induced seesaw model with global U(1)B−L symmetry, in which we consider two component dark matter particles. The dark matter properties are investigated together with some phenomenological constraints such as electroweak precision test, neutrino masses and mixing and lepton flavor violation. In particular, the mixing angle between the Standard Model like Higgs and an extra Higgs is extremely restricted by the direct detection experiment of dark matter. We also discuss the contribution of Goldstone boson to the effective number of neutrino species ΔNeff ≈ 0.39 which has been reported by several experiments.

3.55 keV X-ray line signal from excited dark matter in radiative neutrino model

Abstract We propose a radiative lepton model, in which the charged lepton masses are generated at one-loop level, and the neutrino masses are induced at two-loop level. On the other hand, tau mass is derived at tree level since it is too heavy to generate radiatively. Then we discuss muon anomalous magnetic moment together with the constraint of lepton flavor violation. A large muon magnetic moment is derived due to the vector like charged fermions which are newly added to the standard model. In addition, considering a scalar dark matter in our model, a strong gamma-ray signal is produced by dark matter annihilation via internal bremsstrahlung. We can also obtain the effective neutrino number by the dark radiation of the Goldstone boson coming from the imposed global U ( 1 ) ′ symmetry.

Two loop neutrino model and dark matter particles with global B−L symmetry

We study a radiative inverse seesaw model with local B–L symmetry, in which we extend the neutrino mass structure that is generated through a kind of inverse seesaw framework to the more generic one than our previous work. We focus on the real part of bosonic particle as a dark matter and investigate the features in

Radiative lepton model and dark matter with global

mathcal{ O}mbox {(1--80)}~mbox{GeV}

U(1)'

mass range, reported by the experiments such as CoGeNT and XENON (2012).

symmetry

The search for sharp features in the gamma-ray spectrum is a promising approach to identify a signal from dark matter annihilations over the astrophysical backgrounds. In this paper we investigate the generation of gamma-ray lines and internal bremsstrahlung signals in a toy model where the dark matter particle is a real scalar that couples to a lepton and an exotic fermion via a Yukawa coupling. We show that the Fermi-LAT and H.E.S.S. searches for line-like spectral features severely constrain regions of the parameter space where the scalar dark matter is thermally produced. Finally, we also discuss the complementarity of the searches for sharp spectral features with other indirect dark matter searches, as well as with direct and collider searches.