arXiv subjects

Masahiro Takimoto

Publications and source records attributed to Masahiro Takimoto.

28 records · Page 2Linked to original sources

arXiv2015

Towards a Scale Free Electroweak Baryogenesis

We propose a new electroweak baryogenesis scenario in high-scale supersymmetric (SUSY) models. We consider a singlet extension of the minimal SUSY standard model introducing additional vector-like multiplets. We show that the strongly first-order phase transition can occur at a high temperature comparable to the soft SUSY breaking scale. In addition, the proper amount of the baryon asymmetry of the universe can be generated via the lepton number violating process in the vector-like multiplet sector. The typical scale of our scenario, the soft SUSY breaking scale, can be any value. Thus our new electroweak baryogenesis scenario can be realized at arbitrary scales and we call this scenario as a scale free electroweak baryogenesis. This soft SUSY breaking scale is determined by other requirements. If the soft SUSY breaking scale is O(10) TeV, our scenario is compatible with the observed mass of the Higgs boson and the constraints by the electric dipole moments measurements and the flavor experiments. Furthermore, the singlino can be a good candidate of the dark matter.

hep-ph↗

arXiv2014

Singlino Resonant Dark Matter and 125 GeV Higgs Boson in High-Scale Supersymmetry

We consider a singlino Dark Matter (DM) scenario in a singlet extension model of the Minimal Supersymmetric Standard Model, which is so-called the Nearly MSSM (nMSSM). We find that with high-scale supersymmetry breaking the singlino can obtain a sizable radiative correction to the mass, which opens a window for the DM scenario with resonant annihilation via the exchange of the Higgs boson. We show that the current DM relic abundance and the Higgs boson mass can be explained simultaneously. This scenario can be fully probed by XENON1T.

hep-ph↗

arXiv2014

Correspondence of I- and Q-balls as Non-relativistic Condensates

If a real scalar field is dominated by non-relativistic modes, then it approximately conserves its particle number and obeys an equation that governs a complex scalar field theory with a conserved global U(1) symmetry. From this fact, it is shown that the I-ball (oscillon) can be naturally understood as a projection (e.g., real part) of the non-relativistic Q-ball solution. In particular, we clarify that the stability of the I-ball is guaranteed by the U(1) symmetry in the corresponding complex scalar field theory as long as the non-relativistic condition holds. We also discuss the longevity of I-ball from the perspective of the complex scalar field in terms of U(1) charge violating processes.

hep-ph↗

arXiv2014

Axion Models with High Scale Inflation

We revisit the cosmological aspects of axion models. In the high-scale inflation scenario, the Peccei-Quinn (PQ) symmetry is likely to be restored during/after inflation. If the curvature of the PQ scalar potential at the origin is smaller than its vacuum expectation value; for instance in a class of SUSY axion models, thermal inflation happens before the radial component of the PQ scalar (saxion) relaxes into the global minimum of the potential and the decay of saxion coherent oscillation would produce too much axion dark radiation. In this paper, we study how to avoid the overproduction of axion dark radiation with some concrete examples. We show that, by taking account of the finite-temperature dissipation effect appropriately, the overproduction constraint can be relaxed since the PQ scalar can take part in the thermal plasma again even after the PQ phase transition. We also show that it can be further relaxed owing to the late time decay of another heavy CP-odd scalar, if it is present.

hep-ph↗

arXiv2014

Suppressed Non-Gaussianity in the Curvaton Model

We show that the local type non-Gaussianity in a class of curvaton models is suppressed, i.e. the non-linearity parameters f_{NL} and those related with higher order statistics can be at most O(1), even if the curvaton energy density is subdominant at the decay. This situation is naturally realized in a very simple curvaton potential with quadratic term plus quartic term.

astro-ph.CO↗

arXiv2014

Curvaton Dynamics Revisited

We revisit the dynamics of the curvaton in detail taking account of effects from thermal environment, effective potential and decay/dissipation rate for general field values and couplings. We also consider the curvature perturbation generated through combinations of various effects: large scale modulation of the oscillation epoch, the effective dissipation rate and the timing at which the equation of state changes. In particular, we find that it tends to be difficult to explain the observed curvature perturbation by the curvaton mechanism without producing too large non-Gaussianity if the curvaton energy density is dissipated through thermal effects. Therefore, the interaction between the curvaton and light elements in the thermal plasma should be suppressed in order for the curvaton to survive the thermal dissipation.

hep-ph↗

arXiv2013

Fate of $Z_2$ Symmetric Scalar Field

The evolution of a coherently oscillating scalar field with $Z_2$ symmetry is studied in detail. We calculate the dissipation rate of the scalar field based on the closed time path formalism. Consequently, it is shown that the energy density of the coherent oscillation can be efficiently dissipated if the coupling constant is larger than the critical value, even though the scalar particle is stable due to the $Z_2$ symmetry.

hep-ph↗

arXiv2013

Non-Thermal Production of Wino Dark Matter via the Decay of Long-Lived Particles

We consider supersymmetric models in which the neutral Wino is the lightest superparticle (LSP), and study the possibility that non-thermally produced Wino plays the role of dark matter. The thermal relic density of Wino is smaller than the present mass density of dark matter if wino mass is smaller than 2.9 TeV; however, even with smaller Wino mass, Wino can be the dominant component of dark matter if it is non-thermally produced by the decay of an exotic particle. In order to study such a possibility in detail, we perform a precise calculation of the present mass density of Wino produced by the exotic-particle decay, taking account of the following effects: (i) coannihilation among charged and neutral Winos, and (ii) Sommerfeld effect on the pair annihilation cross section of Winos. We consider several well-motivated cases where the exotic particle corresponds to cosmological moduli fields, gravitino, or axino, and discuss the implication of the Wino LSP for these cases.

hep-ph↗

arXiv2013

Scalar Trapping and Saxion Cosmology

We study in detail the dynamics of a scalar field in thermal bath with symmetry breaking potential. In particular, we focus on the process of trapping of a scalar field at an enhanced symmetry point through the thermal/non-thermal particle production, taking into account the interactions of produced particles with the standard model particles. As an explicit example, we revisit the saxion dynamics with an initial amplitude much larger than the Peccei-Quinn scale and show that the saxion trapping phenomenon happens for the most cases and it often leads to thermal inflation. We also study the saxion dynamics after thermal inflation, and it is shown that thermal dissipation effect on the saxion can relax the axion overproduction problem from the saxion decay.

hep-ph↗

arXiv2012

Thermal Effects on Saxion in Supersymmetric Model with Peccei-Quinn Symmetry

We consider supersymmetric model with Peccei-Quinn symmetry and study effects of saxion on the evolution of the universe, paying particular attention to the effects of thermal bath. The axion multiplet inevitably couples to colored particles, which induces various thermal effects. In particular, (i) saxion potential is deformed by thermal effects, and (ii) coherent oscillation of the saxion dissipates via the interaction with hot plasma. These may significantly affect the evolution of the saxion in the early universe.

hep-ph↗