Browsing by Author "Kobayashi, T"

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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.
Generation of frequency tunable polarization entangled photon pairs
(2006-03-15)
Yabushita, A
;
Kobayashi, T
;
電子物理學系
;
Department of Electrophysics
Photon pairs with correlated frequencies from an optical parametric system were generated by a continuous wave pump focused on a type-II nonlinear crystal with polarization entanglement. The polarization entanglement of the frequency resolved photons was measured under several typical configurations. By optimizing a condition, the degree of polarization entanglement was improved substantially. We proposed the application of the system, which can be used as a light source of wavelength division multiplexing quantum key distribution, optimizing the configuration of the photon-pair generation. (c) 2006 American Institute of Physics.