Shinta Kasuya

Isocurvature fluctuations in the Affleck–Dine mechanism and constraints on inflation models

We argue that, in the Affleck–Dine mechanism, baryonic isocurvature fluctuations are generated in most inflation models in supergravity. The inflationary scale and a reheating temperature are constrained in order not to induce too large baryonic isocurvature fluctuations. In particular, high-scale inflation models with high reheating temperatures are disfavored in this context.

Axion isocurvature fluctuations with extremely blue spectrum

We construct an axion model for generating isocurvature fluctuations with blue spectrum, n{sub iso}=2-4, which is suggested by recent analyses of admixture of adiabatic and isocurvature perturbations with independent spectral indices, n{sub ad}{ne}n{sub iso}. The distinctive feature of the model is that the spectrum is blue at large scales while scale invariant at small scales. This is naturally realized by the dynamics of the Peccei-Quinn scalar field.

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.

Can MSSM particle be the inflaton

Abstract We consider the possibility of using one of the D -flat directions in the minimal supersymmetric standard model (MSSM) as the inflaton. We show that the flat direction consisting of (first generation) left- and right-handed up-squarks as well as the up-type Higgs boson may play the role of the inflaton if dominant part of the up-quark mass is radiatively generated from supersymmetric loop diagrams. We also point out that, if the R -parity violating Yukawa coupling is of O (10 −7 ), R -odd D -flat directions may be another possible candidate of the inflaton. Such inflation models using D -flat directions in the MSSM are not only testable with collider experiments but also advantageous to resolve the problem how the inflaton reheats the Universe.

Entropy production by Q-ball decay for diluting long-lived charged particles

The cosmic abundance of a long-lived charged particle such as a stau is tightly constrained by catalyzed big bang nucleosynthesis. One of the ways to evade the constraints is to dilute these particles with a huge entropy production. We evaluate the dilution factor in a case where non-relativistic matter dominates the energy density of the universe and decays with large entropy production. We find that large Q balls can fulfill this role; they are naturally produced in the gauge-mediated supersymmetry breaking scenario.

511 keV line from Q balls in the galactic center

The 511 keV photons from the galactic center can be explained by positrons produced through Q-ball decay. In the scheme of gauge-mediated supersymmetry breaking, large Q balls with lepton charge are necessarily long-lived. In particular, the lifetime can be as long as (or even longer than) the age of the Universe. If kinematically allowed, such large Q balls decay into positrons, which eventually annihilate with electrons into 511 keV photons. Our scenario is realized within the minimal supersymmetric standard model in the inflationary universe, which is very plausible.

Gravitino dark matter and baryon asymmetry from Q -ball decay in gauge mediation

We investigate the

511 keV line and diffuse gamma rays from moduli

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Revisiting the gravitino dark matter and baryon asymmetry from Q-ball decay in gauge mediation

-ball decay in the gauge-mediated supersymmetry breaking.

IceCube potential for detecting Q-ball dark matter in gauge mediation

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