arXiv subjects

Daijiro Suematsu

Publications and source records attributed to Daijiro Suematsu.

At least 19 recordsLinked to original sources

arXiv2026

Scale invariant radiative neutrino mass model

We propose a scale invariant radiative neutrino mass model with custodial symmetry by introducing two real singlet scalars to the scotogenic model. Masses of an inert doublet scalar and right-handed neutrinos are induced by a vacuum expectation value (VEV) of a singlet scalar caused through the Coleman-Weinberg mechanism.It violates spontaneously both the custodial symmetry and the scale invariance. The weak scale can take a suppressed value compared with the singlet scalar VEV because of the custodial symmetry. In this framework we study phenomenological consequences for neutrino mass, dark matter and baryon number asymmetry by assuming a texture for neutrino Yukawa couplings. Since the required dark matter abundance cannot be explained by a neutral component of the inert doublet scalar in that case, the lightest right-handed neutrino should be dark matter. Mass of the dark matter is predicted to be less than $O(1)$ MeV and baryon number asymmetry could be explained through resonant leptogenesis.

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arXiv2026

Right-handed neutrino dark matter consistent with the generation of baryon number asymmetry

A right-handed neutrino is a promising candidate for dark matter (DM) which has no interaction with nuclei. Since two right-handed neutrinos explain neutrino oscillation data and baryon number asymmetry through both the seesaw mechanism and leptogenesis based on the out-of-equilibrium decay of the lighter one, the lightest third right-handed neutrino could be free from them and stable to be DM. It suggests a possibility that the right-handed neutrinos could be common key particles for the explanation of three problems in the standard model (SM). We study this possibility by analyzing the structure of a neutrino mass matrix in the scotogenic model for neutrino mass.

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arXiv2025

Neutrino models with a zero mass eigenvalue

Absolute values of the neutrino mass are not known still now although their upper bounds are constrained through several experiments and observations. Recent analyses of cosmological observations present severe constraint on the sum of neutrino masses. It might suggest an interesting possibility for the absolute values of neutrino mass and their ordering. In this paper, taking it as a useful hint, we study possible neutrino models with a zero mass eigenvalue from a view point of neutrino oscillation data and baryon number asymmetry in the Universe. We focus our study on the seesaw type mass generation by making a certain assumption for origin of right-handed neutrino mass.

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arXiv2024

Right-handed neutrino as a common progenitor of baryon number asymmetry and dark matter

Cosmological and astrophysical observations suggest that both energy densities of baryon and dark matter take the same order values in the present Universe. We propose a scenario to give an answer for this problem in a scotogenic model and its extension. The model naturally provides dark matter candidates as its crucial ingredients to explain the small neutrino mass. If a neutral component of an inert doublet scalar plays a role of dark matter and leptogenesis occurs at TeV scales, both dark matter abundance and baryon number asymmetry could be explained with a same mother particle. Coincidence between the order of their energy densities might be understood through such a background.

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arXiv2023

$CP$ issues in the SM from a view point of spontaneous $CP$ violation

The standard model (SM) has several issues related to the $CP$ violation which could give clues to search physics beyond the SM. They are a $CP$ phase in the CKM matrix, the strong $CP$ problem, $CP$ phases in the PMNS matrix and $CP$ asymmetry in lepton number violating processes related to baryon number asymmetry. We consider a model which could give a unified explanation for them in a framework of spontaneous $CP$ violation. It is an extension of the SM with vector-like fermions and singlet scalars. In this model, they are explained by a common complex phase caused in the spontaneous $CP$ violation. We present concrete examples for them and also discuss some relevant phenomenology.

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arXiv2023

Inflation caused by a potential valley with CP violation

We propose an inflation scenario caused by an inflaton identified with a potential valley which brings about $CP$ violation in the standard model (SM). If singlet scalars have nonminimal couplings with the Ricci scalar in a suitable way, favorable inflation could be derived through the potential valley composed of such scalars. We study dynamics of the scalars during and after the inflation, which suggests that it could be described as a single field inflation approximately. If these scalars make suitable ingredients of the SM couple with vectorlike fermions and right-handed neutrinos, a CKM phase could be induced and also leptogenesis could occur successfully even at a rather low reheating temperature.

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arXiv2021

Inflation connected to the origin of $CP$ violation

We consider a simple extension of the standard model, which could give a solution for its $CP$ issues such as the origin of both CKM and PMNS phases and the strong $CP$ problem. The model is extended with singlet scalars which could cause spontaneous $CP$ violation to result in these phases at low energy regions. The singlet scalars could give a good inflaton candidate if they have a suitable nonminimal coupling with the Ricci scalar. $CP$ issues and inflation could be closely related through these singlet scalars in a natural way. In a case where inflaton is a mixture of the singlet scalars, we study reheating and leptogenesis as notable phenomena affected by the fields introduced in this extension.

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arXiv2021

Inflation and DM phenomenology in a scotogenic model extended with a real singlet scalar

We study an extension of the scotogenic model with a real singlet scalar. It gives an origin of the mass of right-handed neutrinos and plays a role of inflaton through a non-minimal coupling with Ricci scalar. While an inert doublet scalar is an indispensable ingredient for neutrino mass generation in the model, it is also a promising dark matter (DM) candidate. Introduction of the singlet scalar could affect its nature of DM if mass of the singlet scalar is in a resonance region. We focus our study on such a case where inflaton mass is expected to be in a TeV range and reheating temperature is less than $10^9$ GeV. Thus the model requires low scale leptogenesis. After examining several effects brought about by the singlet scalar for the DM sector, we discuss DM phenomenology such as high energy neutrinos and monochromatic gammas caused by its annihilation.

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arXiv2020

Low scale leptogenesis in a model with promising $CP$ structure

We consider a simple extension of the standard model, which could give a solution to its $CP$ issues through both the Peccei-Quinn mechanism and the Nelson-Barr mechanism. Its low energy effective model coincides with the scotogenic model in the leptonic sector. Although leptogenesis is known not to work well at lower reheating temperature than $10^9$ GeV in simple seesaw and scotogenic frameworks, such low reheating temperature could be consistent with both neutrino mass generation and thermal leptogenesis via newly introduced fields without referring to the resonance effect. An alternative dark matter candidate to axion is prepared as an indispensable ingredient of the model.

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arXiv2019

Low scale leptogenesis in a hybrid model of the scotogenic type I and III seesaw

The scotogenic type I and type III seesaw models are good candidates to explain the existence of neutrino masses and dark matter simultaneously. However, since triplet fermions have SU(2) gauge interaction, they cannot be out of equilibrium before the electroweak symmetry breaking. Thus, leptogenesis seems to be difficult within a framework of the pure type III seesaw model. Some extension seems to be required to solve this fault. A model extended by introducing a singlet fermion could be such a simple example. If the singlet fermion is in the thermal equilibrium even for its extremely small neutrino Yukawa coupling, leptogenesis could be shown to occur successfully for a rather low mass of the singlet fermion. The required mass could be lowered to $10^4$~GeV.

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arXiv2019

Pati-Salam unification with a spontaneous CP violation

Recent neutrino oscillation experiments suggest that the PMNS matrix in the lepton sector has a $CP$ violating phase as the CKM matrix in the quark sector. However, origin of these phases in both matrices are not clarified by now. Although complex Yukawa couplings could induce these phases, they remain as free parameters of the model even in that case. If the $CP$ symmetry is considered to be spontaneously broken, they are expected to be determined by some physics at a much lower energy scale than the Planck scale. We study such a possibility in a framework of Pati-Salam type unification. We also discuss other phenomenological issues in it.

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arXiv2018

An extension of the SM based on effective Peccei-Quinn Symmetry

Peccei-Quinn (PQ) mechanism based on a chiral global U(1) symmetry is considered to be a simple and elegant solution for strong CP problem. Fact that the mechanism could be experimentally examined through the axion search makes it much more interesting and recently it causes a lot of attention again. However, it is also known that the mechanism is annoyed by two serious problems, that is, a domain wall problem and goodness of global symmetry. Any global symmetry is considered not to be exact due to the quantum effect of gravity. In this paper, we consider a solution to these problems, in which quark mass hierarchy and mixing, neutrino mass generation and existence of dark matter are closely related. In our solution, PQ symmetry is assumed to be induced through symmetry breaking at an intermediate scale of a local U(1) symmetry, and a global U(1) symmetry which plays a role of Froggatt-Nielsen symmetry . In the lepton sector, a remnant of the PQ symmetry controls neutrino mass generation and dark matter existence.

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arXiv2018

Dark matter stability and one-loop neutrino mass generation based on Peccei-Quinn symmetry

We propose a model which is a simple extension of the KSVZ invisible axion model with an inert doublet scalar. Peccei-Quinn symmetry forbids tree-level neutrino mass generation and its remnant $Z_2$ symmetry guarantees dark matter stability. The neutrino masses are generated by one-loop effects as a result of the breaking of Peccei-Quinn symmetry through a nonrenormalizable interaction. Although the low energy effective model coincides with an original scotogenic model which contains right-handed neutrinos with large masses, it is free from the strong $CP$ problem.

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arXiv2017

Possible roles of Peccei-Quinn symmetry in an effective low energy model

Strong $CP$ problem is known to be solved by imposing Peccei-Quinn (PQ) symmetry. However, domain wall problem caused by the spontaneous breaking of its remnant discrete subgroup could make models invalid in many cases. We propose a model in which the PQ charge is assigned quarks so as to escape this problem without introducing any extra colored fermions. In the low energy effective model resulting after the PQ symmetry breaking, both the quark mass hierarchy and the CKM mixing could be explained through Froggatt-Nielsen mechanism. If the model is combined with the lepton sector supplemented by an inert doublet scalar and right-handed neutrinos, the effective model reduces to the scotogenic neutrino mass model in which both the origin of neutrino masses and dark matter are closely related. The strong $CP$ problem could be related to the quark mass hierarchy, neutrino masses and dark matter through the PQ symmetry.

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arXiv2017

Symmetry restoration due to preheating and lepton number asymmetry

We study a possible symmetry restoration due to the radiative effect of particles which are explosively produced in preheating after inflation. As its application, we consider a scenario for leptogenesis based on the lepton number asymmetry generated in the right-handed neutrino sector through the inflaton decay. The scenario is examined in a one-loop radiative neutrino mass model extended with singlet scalars.

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arXiv2016

Leptogenesis in a neutrino mass model coupled with inflaton

We propose a scenario for the generation of baryon number asymmetry based on the inflaton decay in a radiative neutrino mass model extended with singlet scalars. In this scenario, lepton number asymmetry is produced through the decay of non-thermal right-handed neutrinos caused from the inflaton decay. Since the amount of non-thermal right-handed neutrinos could be much larger than the thermal ones, the scenario could work without any resonance effect for rather low reheating temperature. Sufficient baryon number asymmetry can be generated for much lighter right-handed neutrinos compared with the Davidson-Ibarra bound.

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arXiv2016

Radiative neutrino mass model with degenerate right-handed neutrinos

The radiative neutrino mass model can relate neutrino masses and dark matter at a TeV scale. If we apply this model to thermal leptogenesis, we need to consider resonant leptogenesis at that scale. It requires both finely degenerate masses for the right-handed neutrinos and a tiny neutrino Yukawa coupling. We propose an extension of the model with a U(1) gauge symmetry, in which these conditions are shown to be simultaneously realized through a TeV scale symmetry breaking. Moreover, this extension can bring about a small quartic scalar coupling between the Higgs doublet scalar and an inert doublet scalar which characterizes the radiative neutrino mass generation. It also is the origin of the $Z_2$ symmetry which guarantees the stability of dark matter. Several assumptions which are independently supposed in the original model are closely connected through this extension.

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arXiv2016

Inflation due to a non-minimal coupling of singlet scalars in the radiative seesaw model

The radiative neutrino mass model with inert doublet dark matter is a promising model for the present experimental issues which cannot be explained within the standard model. We study an extension of this model focusing on cosmological features brought about from the scalar sector. Inflation due to singlet scalars with hierarchical non-minimal couplings with the Ricci scalar may give a favorable solution for both neutrino masses and baryon number asymmetry in the Universe.

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