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Inflation with a constant rate of roll

- H. Motohashi, A. Starobinsky, J. Yokoyama
- Economics
- 18 November 2014

We consider an inflationary scenario where the rate of inflaton roll defined by $\ddot\phi/H\dot \phi$ remains constant. The rate of roll is small for slow-roll inflation, while a generic rate of… Expand

Primordial black holes and slow-roll violation

- H. Motohashi, Wayne Hu
- Physics
- 21 June 2017

For primordial black holes (PBH) to be the dark matter in single-field inflation, the slow-roll approximation must be violated by at least $\mathcal{O}(1)$ in order to enhance the curvature power… Expand

Exact black hole solutions in shift-symmetric quadratic degenerate higher-order scalar-tensor theories

- H. Motohashi, M. Minamitsuji
- PhysicsPhysical Review D
- 26 March 2019

We find various exact black hole solutions in the shift-symmetric subclass of the quadratic degenerate higher-order scalar-tensor (DHOST) theories with linearly time dependent scalar field whose… Expand

Constant-roll inflation: Confrontation with recent observational data

- H. Motohashi, A. Starobinsky
- Economics
- 20 February 2017

The previously proposed class of phenomenological inflationary models in which the assumption of inflaton slow-roll is replaced by the more general, constant-roll condition is compared with the most… Expand

Linear stability analysis of hairy black holes in quadratic degenerate higher-order scalar-tensor theories: Odd-parity perturbations

- Kazufumi Takahashi, H. Motohashi, M. Minamitsuji
- MathematicsPhysical Review D
- 7 April 2019

We study static spherically symmetric black hole solutions with a linearly time-dependent scalar field and discuss their linear stability in the shift- and reflection-symmetric subclass of quadratic… Expand

Ultra Slow-Roll Inflation and the non-Gaussianity Consistency Relation

- Jérôme Martin, H. Motohashi, Teruaki Suyama
- Computer Science
- 1 November 2012

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f(R) constant-roll inflation

- H. Motohashi, A. Starobinsky
- Physics
- 26 April 2017

The previously introduced class of two-parametric phenomenological inflationary models in general relativity in which the slow-roll assumption is replaced by the more general, constant-roll condition… Expand

Stealth Schwarzschild solution in shift symmetry breaking theories

- M. Minamitsuji, H. Motohashi
- PhysicsPhysical Review D
- 18 September 2018

We find stealth Schwarzschild solutions with a nontrivial profile of the scalar field regular on the horizon in the Einstein gravity coupled to the scalar field with the k-essence and/or generalized… Expand

Generalized Slow Roll in the Unified Effective Field Theory of Inflation

- H. Motohashi, Wayne Hu
- Mathematics
- 4 April 2017

We provide a compact and unified treatment of power spectrum observables for the effective field theory (EFT) of inflation with the complete set of operators that lead to second-order equations of… Expand

On rotating black holes in DHOST theories

- J. B. Achour, Hongguang Liu, H. Motohashi, S. Mukohyama, K. Noui
- Physics
- 12 June 2020

Using the disformal solution-generating method, we construct new axisymmetric solutions in Degenerate Higher Order Scalar Tensor (DHOST) theories. The method consists in first considering a "seed"… Expand

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