334 citations · 4k across the 75 of their papers we have counts for
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Inflation with a constant rate of roll
Hayato Motohashi, Alexei A. Starobinsky, Jun'ichi Yokoyama
We consider an inflationary scenario where the rate of inflaton roll defined by remains constant. The rate of roll is small for slow-roll inflation, while a generi…
Third order equations of motion and the Ostrogradsky instability
Hayato Motohashi, Teruaki Suyama
It is known that any nondegenerate Lagrangian containing time derivative terms higher than first order suffers from the Ostrogradsky instability, pathological excitation of positiv…
Consistency relation for inflation
Hayato Motohashi
We consider inflation with , allowing small deviation from inflation. Using the inflaton potential in the Einstein frame, we construct a consistency relati…
Stability of cosmological solutions in extended quasidilaton massive gravity
Hayato Motohashi, Wayne Hu
We consider the stability of self-accelerating solutions to extended quasidilaton massive gravity in the presence of matter. By making a second or extended fiducial metric dynamica…
Black hole perturbation in the most general scalar-tensor theory with second-order field equations II: the even-parity sector
Tsutomu Kobayashi, Hayato Motohashi, Teruaki Suyama
We perform a fully relativistic analysis of even-parity linear perturbations around a static and spherically symmetric solution in the most general scalar-tensor theory with second…
Loop contribution to inflationary magnetic field
Hayato Motohashi, Teruaki Suyama
Within the framework of the standard quantum electrodynamics, we compute contribution of vacuum polarization at one-loop order to the power spectrum of the magnetic field on inflat…