Daijiro Suematsu

Cold dark matter, radiative neutrino mass, μ → eγ, and neutrinoless double beta decay

Two of the most important and pressing questions in cosmology and particle physics are: (1) what is the nature of cold dark matter? and (2) will near-future experiments on neutrinoless double beta decay be able to ascertain that the neutrino is a Majorana particle, i.e. its own antiparticle? We show that these two seemingly unrelated issues are intimately connected if neutrinos acquire mass only because of their interactions with dark matter.

Radiative seesaw model : Warm dark matter, collider signatures, and lepton flavor violating signals

INTRODUCTION: Solar [1], atmospheric [2], and reactor [3] neutrino experiments have demonstrated that neutrinos have mass and nonzero mixing angles among the different generations. On the other hand, observations of the cosmic microwave background, primordial abundances of light elements, and large scale structure formation have firmly established that most of the mass of the Universe consists of dark matter (DM) [4]. These experimental results are at present the most important evidences for physics beyond the standard model. There are several ways in which neutrino masses can be generated. Certainly the best-known mechanism to generate small Majorana neutrino masses is the seesaw [5]. However, a large variety of models exists in which lepton number is broken near or at the electroweak scale. Examples are supersymmetric models with explicit or spontaneous breaking of R parity [6,7], models with Higgs triplets [8], pure radiative models at one-loop [9] or at two-loop [10] order, and models in which neutrino masses are induced by leptoquark interactions [11].

FERMION TRIPLET DARK MATTER AND RADIATIVE NEUTRINO MASS

The neutral member of a Majorana fermion triplet (Σ+, Σ0, Σ-) is proposed as a candidate for the dark matter of the Universe. It may also serve as the seesaw anchor for obtaining a radiative neutrino mass.

Reconciliation of CDM abundance and mu ---> e gamma in a radiative seesaw model

We reexamine relic abundance of a singlet fermion as a CDM candidate, which contributes to the neutrino mass generation through radiative seesaw mechanism. We search solutions for Yukawa couplings and the mass spectrum of relevant fields to explain neutrino oscillation data. For such solutions, we show that an abundance of a lightest singlet fermion can be consistent with WMAP data without conflicting with both bounds of

Neutrino masses and CDM in a non-supersymmetric model

\mu\to e\gamma

Anomaly induced dark matter decay and PAMELA/ATIC experiments

and

Enhancement of the annihilation of dark matter in a radiative seesaw model

\tau\to \mu\gamma

Baryon number asymmetry and dark matter in the neutrino mass model with an inert doublet

. This reconciliation does not need any modification of the original radiative seesaw model other than by specifying flavor structure of Yukawa couplings and taking account of coannihilation effects.

Mass Bound of the Lightest Neutral Higgs Scalar in the Extra

Abstract We propose a model for neutrino mass generation based on both the tree-level seesaw mechanism with a single right-handed neutrino and one-loop radiative effects in a non-supersymmetric framework. The generated mass matrix is composed of two parts which have the same texture and produce neutrino mass eigenvalues and mixing suitable for the explanation of neutrino oscillations. The model has a good CDM candidate which contributes to the radiative neutrino mass generation. The stability of the CDM candidate is ensured by Z 2 which is the residual symmetry of a spontaneously broken U ( 1 ) ′ . We discuss the values of U e 3 and also estimate the masses of the relevant fields to realize an appropriate abundance of the CDM.

U(1)

Abstract The cosmic ray data of PAMELA/ATIC may be explained by dark matter decay with a decay rate τ DM − 1 ∼ 10 − 26 s − 1 ∼ 10 − 45 eV , an energy scale which could not be understood within the framework of the standard model or its simple supersymmetric extension. We propose anomaly induced dark matter decay to exponentially suppress the decay rate, and apply to a supersymmetric extension of the Mas inert Higgs model of the radiative seesaw mechanism for neutrino masses. In this model the lightest right-handed neutrino ψ N and the lightest neutralino χ can fill the observed necessary dark matter relic, and we find that ψ N can decay into χ through anomaly with a right order of decay rate, emitting only leptons. All the emitted positrons are right-handed.