Nonthermal dark matter models and signals

Okada, Hiroshi,Orikasa, Yuta,Toma, Takashi American Physical Society 2016 Physical Review D Vol.93 No.5

<P>Many experiments exploring weakly interacting massive particles (WIMPs) such as direct, indirect and collider searches have been carried out until now. However, a clear signal of a WIMP has not been found yet and it makes us to suspect that WIMPs are questionable as a dark matter candidate. Taking into account this situation, we propose two models in which dark matter relic density is produced by decay of a metastable particle. In the first model, the metastable particle is a feebly interacting massive particle, which is the so-called FIMP, produced by freeze-in mechanism in the early universe. In the second model, the decaying particle is thermally produced the same as the usual WIMP. However decay of the particle into dark matter is led by a higher dimensional operator. As a phenomenologically interesting feature of nonthermal dark matter discussed in this paper, a strong sharp gamma-ray emission as an indirect detection signal occurs due to internal bremsstrahlung, although some parameter space has already been ruled out by this process. Moreover combining other experimental and theoretical constraints such as dark matter relic density, big bang nucleosynthesis, collider, gamma-rays and perturbativity of couplings, we discuss the two nonthermal DM models.</P>

Two-loop neutrino model with exotic leptons

Okada, Hiroshi,Orikasa, Yuta American Physical Society 2016 Physical Review D Vol.93 No.1

Classically conformal radiative neutrino model with gauged B-L symmetry

Okada, H.,Orikasa, Y. North-Holland Pub. Co 2016 Physics letters. Section B Vol.760 No.-

We propose a classically conformal model in a minimal radiative seesaw, in which we employ a gauged B-L symmetry in the standard model that is essential in order to work the Coleman-Weinberg mechanism well that induces the B-L symmetry breaking. As a result, nonzero Majorana mass term and electroweak symmetry breaking simultaneously occur. In this framework, we show a benchmark point to satisfy several theoretical and experimental constraints. Here theoretical constraints represent inert conditions and Coleman-Weinberg condition. Experimental bounds come from lepton flavor violations (especially μ→eγ), the current bound on the Z<SUP>'</SUP> mass at the CERN Large Hadron Collider, and neutrino oscillations.

X-ray line in radiative neutrino model with globalU(1)symmetry

Okada, Hiroshi,Orikasa, Yuta American Physical Society 2014 PHYSICAL REVIEW D - Vol.90 No.7

Higgs phenomenology in the minimalSU(3)L×U(1)Xmodel

Okada, Hiroshi,Okada, Nobuchika,Orikasa, Yuta,Yagyu, Kei American Physical Society 2016 Physical Review D Vol.94 No.1

<P>We investigate the phenomenology of a model based on the SU(3)(c) x SU(3)(L) x U(1)(X) gauge theory, the so-called 331 model. In particular, we focus on the Higgs sector of the model which is composed of three SU(3)L triplet Higgs fields and is the minimal form for realizing a phenomenologically acceptable scenario. After the spontaneous symmetry breaking SU(3)(L) x U(1)(X) -> SU(2)(L) x U(1)(Y), our Higgs sector effectively becomes that with two SU(2)(L) doublet scalar fields, in which the first-and the second-generation quarks couple to a different Higgs doublet from that which couples to the third-generation quarks. This structure causes the flavor-changing neutral current mediated by Higgs bosons at the tree level. By taking an alignment limit of the mass matrix for the CP-even Higgs bosons, which is naturally realized in the case with the breaking scale of SU(3)(L) x U(1)(X) much larger than that of SU(2)(L) x U(1)(Y), we can avoid current constraints from flavor experiments such as the B-0-(B) over bar (0) mixing even for the Higgs bosons masses that are O(100) GeV. In this allowed parameter space, we clarify that a characteristic deviation in quark Yukawa couplings of the Standard Model-like Higgs boson is predicted, which has a different pattern from that seen in two Higgs doublet models with a softly broken Z(2) symmetry. We also find that the flavor-violating decay modes of the extra Higgs boson, e.g., H/A -> tc and H-+/- -> ts, can be dominant, and they yield the important signature to distinguish our model from the two Higgs doublet models.</P>

Radiative neutrino model with SU(2)L triplet fields

Nomura, Takaaki,Okada, Hiroshi,Orikasa, Yuta American Physical Society 2016 Physical Review D Vol.94 No.11

<P>We propose a loop-induced neutrino mass model, in which we introduce several exotic fermions and bosons with an SU(2)(L) multiplet, and discuss various phenomenologies such as lepton flavor violations, the muon anomalous magnetic moment, nonstandard interacting neutrinoless double beta decay, the relic density of dark matter, and the possibility of the spin-independent direct detection searches, imposing the constraints of oblique parameters. And we show a benchmark point to satisfy all the constraints and discuss our predictions.</P>

Radiative neutrino mass in alternative left–right model

Nomura, Takaaki,Okada, Hiroshi,Orikasa, Yuta Springer-Verlag 2017 European Physical Journal C Vol.77 No.2

<P>We propose a radiative seesaw model in an alternative left-right model without any bidoublet scalar fields, in which all the fermion masses in the standard model are generated through a canonical seesaw mechanism at the tree level. On the other hand the observed neutrino masses are generated at two-loop level. In this paper we focus on the neutrino sector and show how to induce the active neutrino masses. Then we discuss the observed neutrino oscillation, constraints from lepton flavor violations, new sources of the muon anomalous magnetic moment, a long-lived dark matter candidate with keV scale mass, and collider physics.</P>

SU(2)Lseptet scalar linking to a radiative neutrino model

Nomura, Takaaki,Okada, Hiroshi,Orikasa, Yuta American Physical Society 2016 Physical Review D Vol.94 No.5

<P>We study a radiative neutrino model with a SU(2) septet scalar with hypercharge Y = 2 where active neutrino mass is induced at a one-loop level. Calculating a one-loop diagram, mass matrices for an active neutrino are derived. We also analyze lepton flavor violations, the anomalous magnetic moment of a muon, and the flavor-violating Higgs decay h -> mu tau. Then, sizable muon g - 2 and similar to 1% of BR(h -> mu tau) could be obtained in our setup. Furthermore, the collider signature of the septet is discussed, and we focus on the quadratically charged scalar at the LHC 14 TeV. We find that it could be discovered up to 1.5 TeV mass by searching multicharged lepton signal events.</P>

Radiative seesaw mechanism in a minimal 3-3-1 model

Okada, Hiroshi,Okada, Nobuchika,Orikasa, Yuta American Physical Society 2016 Physical Review D Vol.93 No.7

<P>We study the neutrino sector in a minimal SU(3)(L) x U(1)(X) model, in which its mass is generated at a one-loop level with the charged lepton mass, and hence, there exists a strong correlation between the charged-lepton mass and the neutrino mass. We identify the parameter region of this model to satisfy the current neutrino oscillation data as well as the constraints on lepton flavor violating processes. We also discuss a possibility to explain the muon anomalous magnetic moment.</P>

Discriminative phenomenological features of scale invariant models for electroweak symmetry breaking

Hashino, K.,Kanemura, S.,Orikasa, Y. North-Holland Pub. Co 2016 Physics letters. Section B Vol.752 No.-

<P>Classical scale invariance (CSI) may be one of the solutions for the hierarchy problem. Realistic models for electroweak symmetry breaking based on CSI require extended scalar sectors without mass terms, and the electroweak symmetry is broken dynamically at the quantum level by the Coleman-Weinberg mechanism. We discuss discriminative features of these models. First, using the experimental value of the mass of the discovered Higgs boson h(125), we obtain an upper bound on the mass of the lightest additional scalar boson (similar or equal to 543 GeV), which does not depend on its isospin and hypercharge. Second, a discriminative prediction on the Higgs-photon-photon coupling is given as a function of the number of charged scalar bosons, by which we can narrow down possible models using current and future data for the di-photon decay of h(125). Finally, for the triple Higgs boson coupling a large deviation (similar to+70%) from the SM prediction is universally predicted, which is independent of masses, quantum numbers and even the number of additional scalars. These models based on CSI can be well tested at LHC Run II and at future lepton colliders. (C) 2015 The Authors. Published by Elsevier B.V.</P>