Searcharxiv⌕ Search

arXiv subjects

S. Kasuya

Publications and source records attributed to S. Kasuya.

17 recordsLinked to original sources
arXiv2004

Early reionization by decaying particles and cosmic microwave background radiation

We study the reionization scenario in which ionizing UV photons emitted from decaying particle, in addition to usual contributions from stars and quasars, ionize the universe. It is found that the scenario is consistent with both the first year data of the Wilkinson Microwave Anisotropy Probe and the fact that the universe is not fully ionized until z \sim 6 as observed by Sloan Digital Sky Survey. Likelihood analysis revealed that rather broad parameter space can be chosen. This scenario will be discriminated by future observations, especially by the EE polarization power spectrum of cosmic microwave background radiation.

astro-ph↗
arXiv2003

MSSM curvaton in the gauge-mediated SUSY breaking

We study the curvaton scenario using the MSSM flat directions in the gauge-mediated SUSY breaking model. We find that the fluctuations in the both radial and phase directions can be responsible for the density perturbations in the universe through the curvaton mechanism. Although it has been considered difficult to have a successful curvaton scenario with the use of those flat directions, it is overcome by taking account of the finite temperature effects, which induce a negative thermal logarithmic term in the effective potential of the flat direction.

hep-ph↗
arXiv2003

Partially ionizing the universe by decaying particles

We show that UV photons produced by decaying particles can partially reionize the universe and explain the large optical depth observed by Wilkinson Microwave Anisotropy Probe. Together with UV fluxes from early formed stars and quasars, it is possible that the universe is fully ionized at z \lesssim 6 and partially ionized at z \gtrsim 6 as observed by Sloan Digital Sky Survey for large parameter space of the decaying particle. This scenario will be discriminated by future observations, especially by the EE polarization power spectrum of cosmic microwave background radiation.

astro-ph↗
arXiv2003

Affleck-Dine mechanism with negative thermal logarithmic potential

We investigate whether the Affleck-Dine (AD) mechanism works when the contribution of the two-loop thermal correction to the potential is negative in the gauge-mediated supersymmetry breaking models. The AD field is trapped far away from the origin by the negative thermal correction for a long time until the temperature of the universe becomes low enough. The most striking feature is that the Hubble parameter becomes much smaller than the mass scale of the radial component of the AD field, during the trap. Then, the amplitude of the AD field decreases so slowly that the baryon number is not fixed even after the onset of radial oscillation. The resultant baryon asymmetry crucially depends on whether the Hubble parameter, $H$, is larger than the mass scale of the phase component of the AD field, $M_θ$, at the beginning of oscillation. If $H < M_θ$ holds, the formation of Q balls plays an essential role to determine the baryon number, which is found to be washed out due to the nonlinear dynamics of Q-ball formation. On the other hand, if $H > M_θ$ holds, it is found that the dynamics of Q-ball formation does not affect the baryon asymmetry, and that it is possible to generate the right amount of the baryon asymmetry.

hep-ph↗
arXiv2003

I-balls

We find that there exists a soliton-like solution ``I-ball'' in theories of a real scalar field if the scalar potential satisfies appropriate conditions. Although the I-ball does not have any topological or global U(1) charges, its stability is ensured by the adiabatic invariance for the oscillating field.

hep-ph↗
arXiv2002

Affleck-Dine baryogenesis and the Q-ball dark matter in the gauge-mediated SUSY breaking

We consider the Affleck-Dine baryogenesis comprehensively in the minimal supersymmetric standard model with gauge-mediated supersymmetry breaking. Considering the high temperature effects, we see that the Affleck-Dine field is naturally deformed into the form of the Q ball. In the natural scenario where the initial amplitude of the field and the A-terms are both determined by the nonrenormalizable superpotential, we obtain a narrow allowed region in the parameter space in order to explain the baryon number and the dark matter of the universe simultaneously. Therefore, the Affleck-Dine baryogenesis is successful, although difficult.

hep-ph↗
arXiv2001

Q-ball formation: Obstacle to Affleck-Dine baryogenesis in the gauge-mediated SUSY breaking ?

We consider the Affleck-Dine baryogenesis comprehensively in the minimal supersymmetric standard model with gauge-mediated supersymmetry breaking. Considering the high temperature effects, we see that the Affleck-Dine field is naturally deformed into the form of the Q ball. In the natural scenario where the initial amplitude of the field and the A-terms are both determined by the nonrenormalizable superpotential, we obtain only very a narrow allowed region in the parameter space in order to explain the baryon number of the universe for the case that the Q-ball formation occurs just after baryon number production. Moreover, most of the parameter sets suited have already been excluded by current experiments. We also find new situations in which the Q-ball formation takes place rather late compared with baryon number creation. This situation is more preferable, since it allows a wider parameter region for naturally consistent scenarios, although it is still difficult to realize in the actual cosmological scenario.

hep-ph↗
arXiv2001

On the Moduli Problem and Baryogenesis in Gauge-mediated SUSY Breaking Models

We investigate whether the Affleck-Dine mechanism can produce sufficient baryon number of the universe in the gauge-mediated SUSY breaking models, while evading the cosmological moduli problem by late-time entropy production. We find that the Q-ball formation renders the scenario very difficult to work, irrespective of the detail mechanism of the entropy production.

hep-ph↗
arXiv2001

Difficulty of a spinning complex scalar field to be dark energy

We comment on the possibility of a spinning complex scalar field to be dark energy. We show that it deforms (almost) completely into a nontopological soliton state, a Q ball, and the equation of state becomes that of the matter or radiation, depending on the fate of the Q ball. Thus, the spinning complex scalar field is usually very difficult to play the role of the dark energy. We also show the general condition that the spinning complex scalar field can successfully be the dark energy.

astro-ph↗
arXiv2000

New type of stable Q balls in the gauge-mediated supersymmetry breaking

We obtain a new type of a stable Q ball in the context of gauge-mediated supersymmetry breaking in minimal supersymmetric standard model. It is so-called gravity-mediation type of Q ball, but stable against the decay into nucleons, since the energy per unit charge is equal to gravitino mass m_{3/2}, which can be smaller than nucleon mass in the gauge-mediation mechanism. We consider the cosmological consequences in this new Q-ball scenario, and find that this new type of the Q ball can be considered as the dark matter and the source for the baryon number of the universe simultaneously.

hep-ph↗
arXiv2000

Q-ball formation in the gravity-mediated SUSY breaking scenario

We study the formation of Q-balls which are made of flat directions that appear in the supersymmetric extension of the standard model in the context of gravity-mediated supersymmetry breaking. The full non-linear calculations for the dynamics of the complex scalar field are made. Since the scalar potential in this model is flatter than ϕ^2, we have found that fluctuations develop and go non-linear to form non-topological solitons, Q-balls. The size of a Q-ball is determined by the most amplified mode, which is completely determined by the model parameters. On the other hand, the charge of Q-balls depends linearly on the initial charge density of the Affleck-Dine (AD) field. Almost all the charges are absorbed into Q-balls, and only a tiny fraction of the charges is carried by a relic AD field. It may lead to some constraints on the baryogenesis and/or parameters in the particle theory. The peculiarity of gravity-mediation is the moving Q-balls. This results in collisions between Q-balls. It may increase the charge of Q-balls, and change its fate.

hep-ph↗
arXiv2000

Remarks on Cosmic String Formation during Preheating on Lattice Simulations

We reconsider the formation of (global) cosmic strings during and after preheating by calculating the dynamics of a scalar field on both two- and three- dimensional lattices. We have found that there is little differences between the results in two and three dimensions about the dynamics of fluctuations, at least, during preheating. Practically, it is difficult to determine whether long cosmic strings which may affect the later evolution of the universe could ever be produced from the results of simulations on three-dimensional lattices with smaller box sizes than the horizon. Therefore, using two-dimensional lattices with large box size, we have found that cosmic strings with the breaking scale 0η\sim 10^{16} GeV are produced for broad range of parameter space in η, while for higher breaking scales (η\sim 3\times 10^{16} GeV), their production depends crucially on the value of the breaking scale ηin our simulations.

hep-ph↗
arXiv2000

Q-ball Formation through Affleck-Dine Mechanism

We present the full nonlinear calculation of the formation of a Q-ball through the Affleck-Dine (AD) mechanism by numerical simulations. It is shown that large Q-balls are actually produced by the fragmentation of the condensate of a scalar field whose potential is very flat. We find that the typical size of a Q-ball is determined by the most developed mode of linearized fluctuations, and almost all the initial charges which the AD condensate carries are absorbed into the formed Q-balls, whose sizes and the charges depend only on the initial charge densities.

hep-ph↗
arXiv1998

Topological Defects Formation after Inflation on Lattice Simulation

We consider the formation of topological defects after inflation. In order to take into account the effects of the rescattering of fluctuations, we integrate the classical equation that describes the evolution of a complex scalar field on the two-dimensional lattice with a slab symmetry. The growth of fluctuations during preheating is found not to be enough for defect formation, and rather a long stage of the rescattering of fluctuations after preheating is necessary. We conclude that the topological defects are not formed if the breaking scale ηis lager than \sim (2 - 3)\times 10^{16} GeV.

hep-ph↗
arXiv1997

Can topological defects be formed during preheating ?

We study the dynamics of a scalar field Φwith the potential g(|Φ|^2-η^2)^2/2 (g=self-coupling constant, η=symmetry breaking scale) after inflation and make clear whether topological defects can ever be formed during preheating. In particular, we pay attention to GUT defects (η\sim 10^{15}GeV - 10^{17}GeV), and consider three types of fluctuations. The first one is produced due to parametric resonance, the second is due to the negative curvature of the potential, and the last is created during inflation. We search for the parameter region that nonthermal fluctuations of the scalar field produced through the parametric resonant decay of its homogeneous part do not lead to defect formation. We find that this region is rather wide, and the GUT defects are not produced after inflation. This fact shows that the positiveness of the effective mass square of the field and production of large fluctuations whose amplitude is as large as that of homogeneous mode are not enough conditions for full symmetry restoration.

hep-ph↗
arXiv1997

Domain Wall Problem of Axion and Isocurvature Fluctuations in Chaotic Inflation Models

We study the domain wall problem of an axion in chaotic inflation models. We show that the production of domain walls does not occurs if the Peccei-Quinn scalar has a flat potential and its breaking $F_{a}$ is larger than $\sim 10^{15}$GeV. We find that too large isocurvature fluctuations are produced for such high $F_{a}$. In order for those isocurvature fluctuations to be consistent with observations of the large scale structure of the universe, the self-coupling constant $g$ and the breaking scale of the Peccei-Quinn scalar should be $g \simeq (1-2.8)\times 10^{-13}$ and $F_{a} \simeq (0.6-1.5)\times 10^{15}$GeV, respectively. In particular the value of self-coupling constant is almost the same as that required for a chaotic inflation, which strongly suggests that the Peccei-Quinn scalar itself is an inflaton.

hep-ph↗
arXiv1997

Cosmological Axion Problem in Chaotic Inflationary Universe

We investigate two cosmological axion problems (isocurvature fluctuations and domain-wall formation) in chaotic inflationary universe. It is believed that these problems are solved if potential for the Peccei-Quinn scalar field is very flat. However, we find that too many domain walls are produced through parametric resonance decay of the Peccei-Quinn scalar field. Only the axion model with N=1(N: QCD anomaly factor) is consistent with observations. We also point out that the flat potential is naturally obtained in a supersymmetric extension of the Peccei-Quinn model. If Peccei-Quinn breaking scale $F_a$ is about 10^{12} GeV, this model predicts anisotropies of cosmic microwave background radiation due to the axion isocurvature fluctuations which may be detectable in future observations.

hep-ph↗