Browsing by Author "Seto, O"

Now showing 1 - 7 of 7

Affleck-dine baryogenesis in a string model
(2004-05-30)
Dolgov, AD
;
Kohri, K
;
Seto, O
;
Yokoyama, J
;
物理研究所
Entropy production by a dilaton decay is studied in the model where the dilaton acquires potential via gaugino condensation in the hidden gauge group. Its effect on the Affleck-Dine baryogenesis is investigated. It is shown that the baryon asymmetry produced by this mechanism with the higher-dimensional terms is diluted by the dilaton decay and can be regulated to the observed value.
Brane world cosmological solution to the gravitino problem
(2005-01-01)
Okada, N
;
Seto, O
;
物理研究所
;
Institute of Physics
We investigate the thermal production of gravitinos in the context of the brane world cosmology. Since the expansion law is modified from the one in the standard cosmology, the Boltzmann equation for the gravitino production is altered. We find that the late-time gravitino abundance is proportional to the "transition temperature", at which the modified expansion law in the brane world cosmology is connecting with the standard one, rather than the reheating temperature after inflation as in the standard cosmology. This means that, even though the reheating temperature is very high, we can avoid the overproduction of gravitinos by taking the transition temperature low enough. Therefore, the gravitino problem can be solved.
D-term inflation and nonperturbative Kahler potential of dilaton
(2004-07-01)
Higaki, T
;
Kobayashi, T
;
Seto, O
;
物理研究所
;
Institute of Physics
We study the D-term inflation scenario with a nonperturbative Kahler potential of the dilaton field. Although the FI term which leads an inflationary expansion is given by the derivative of the Kahler potential with respect to the dilaton in heterotic string models with anomalous U(1), the too large magnitude is problematic for a viable D-term inflation. In this paper, we point out that the Kahler potential with a nonperturbative term can reduce the magnitude of FI term to desired values while both the dilaton stabilization and D-term domination in the potential are realized by nonperturbative superpotential.
Dilaton and moduli fields in D-term inflation
(2004-01-01)
Kobayashi, T
;
Seto, O
;
物理研究所
;
Institute of Physics
We investigate the possibility of D-term inflation within the framework of type-I string-inspired models. Although the D-term inflation model has the excellent property that it is free of the so-called eta problem, two serious problems appear when we embed D-term inflation in string theory: the magnitude of the FI term and the rolling motion of the dilaton. In the present paper, we analyze the potential of D-term inflation in type-I-inspired models and study the behavior of dilaton and twisted moduli fields. Adopting the nonperturbative superpotential induced by gaugino condensation, the twisted moduli can be stabilized. If the dilaton is in a certain range, it evolves very slowly and does not run away to infinity. Thus D-term-dominated vacuum energy becomes available for driving inflation. By studying the density perturbation generated by the inflation model, we derive the constraints on model parameters and give some implications on D-term inflation in type-I-inspired models.
Neutralino dark matter in brane world cosmology
(2005-03-01)
Nihei, T
;
Okada, N
;
Seto, O
;
物理研究所
;
Institute of Physics
The thermal relic density of neutralino dark matter in the brane world cosmology is studied. Since the expansion law at a high energy regime in the brane world cosmology is modified from the one in the standard cosmology, the resultant relic density can be altered. It has been found that, if the five-dimensional Planck mass M-5 is lower than 10(4) TeV, the brane world cosmological effect is significant at the decoupling time, and the resultant relic density is enhanced. We calculate the neutralino relic density in the constrained minimal supersymmetric standard model and show that the allowed region is dramatically modified from the one in the standard cosmology and eventually disappears as M-5 is decreasing. We also find a new lower bound on M-5 greater than or similar to 600 TeV based on the neutralino dark matter hypothesis, namely, the lower bound in order for the allowed region of neutralino dark matter to exist.
Phenomenology of a TeV right-handed neutrino and the dark matter model
(2004-06-01)
Cheung, KM
;
Seto, O
;
物理研究所
;
Institute of Physics
In a model of a TeV right-handed (RH) neutrino by Krauss, Nasri, and Trodden, the sub-eV scale neutrino masses are generated via a three-loop diagram with the vanishing seesaw mass forbidden by a discrete symmetry, and the TeV mass RH neutrino is simultaneously a novel candidate for cold dark matter. However, we show that with a single RH neutrino it is not possible to generate two mass-square differences as required by the oscillation data. We extend the model by introducing one more TeV RH neutrino and show that it is possible to satisfy the oscillation pattern within the modified model. After studying in detail the constraints coming from the dark matter, lepton flavor violation, the muon anomalous magnetic moment, and the neutrinoless double beta decay, we explore the parameter space and derive predictions of the model. Finally, we study the production and decay signatures of the TeV RH neutrinos at TeV e(+)e(-)/mu(+)mu(-) colliders.
Relic density of dark matter in brane world cosmology
(2004-10-01)
Okada, N
;
Seto, O
;
物理研究所
;
Institute of Physics
We investigate the thermal relic density of cold dark matter in the context of brane world cosmology. Since the expansion law in a high energy regime is modified from the one in the standard cosmology, if the dark matter decouples in such a high energy regime its relic number density is affected by this modified expansion law. We derive analytic formulas for the number density of dark matter. It is found that the resultant relic density is characterized by the "transition temperature" at which the modified expansion law in brane world cosmology is connecting with the standard one, and can be considerably enhanced compared to that in the standard cosmology, if the transition temperature is low enough.