3 papers
gr-qc2026
Geometric deformations of symmetric spacetimes with a string cloud
Hiroshi Kozaki, Satsuki Matsuno, Tatsuhiko Koike +2
We establish a deformation framework for highly symmetric solutions to the Einstein equations. In this framework, four-dimensional metrics are constructed from three-dimensional η…
math-ph2026
Timescale for macroscopic equilibration in isolated quantum systems: a rigorous derivation for free fermions
Takashi Hara, Tatsuhiko Koike
For a class of translation-invariant free-fermion systems (including those with uniform nearest neighbor hopping) on a -dimensional hypercubic lattice…
gr-qc2024
Spacetime constructed from a contact manifold with a degenerate metric
Hiroshi Kozaki, Hideki Ishihara, Tatsuhiko Koike +1
We construct a four-dimensional spacetime using a three-dimensional contact manifold equipped with a degenerate metric. The degenerate metric is set to be compatible with the conta…