We discuss black holes in an effective theory derived from a superstring model, which includes a dilaton field, a gauge field and the Gauss-Bonnet term. Assuming U(1) or SU(2) symmetry for the gauge...
Massive fermion production in nonsingular superstring cosmology (2001)
Tsujikawa, Shinji, Yajima, Hiroki
We study massive spin-1/2 fermion production in nonsingular superstring cosmology, taking into account one-loop quantum corrections to a superstring effective action with dilaton and modulus fields....
New constraints on multi-field inflation with nonminimal coupling (2000)
Tsujikawa, Shinji, Yajima, Hiroki
We study the dynamics and perturbations during inflation and reheating in a multi-field model where a second scalar field $\chi$ is nonminimally coupled to the scalar curvature $(\frac12 \xi...
Black hole solutions in Euler-Heisenberg theory (2000)
Yajima, Hiroki, Tamaki, Takashi
We construct static and spherically symmetric black hole solutions in the Einstein-Euler-Heisenberg (EEH) system which is considered as an effective action of a superstring theory. We considered...
Generality of Singularity Avoidance in Superstring Theory: Anisotropic Case (1999)
Yajima, Hiroki, Maeda, Kei-ichi, Ohkubo, Hidetoshi
In one-loop string effective action, we study a generality of non-singular cosmological solutions found in the isotropic and homogeneous case. We discuss Bianchi I and IX type spacetimes. We find...
Dilatonic Black Holes with Gauss-Bonnet Term (1996)
Torii, Takashi, Yajima, Hiroki, Maeda, Kei-ichi
We discuss black holes in an effective theory derived from a superstring model, which includes a dilaton field, a gauge field and the Gauss-Bonnet term. Assuming U(1) or SU(2) symmetry for the gauge...