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Primordial Black Holes as Dark Matter through Higgs Criticality
Samuel Passaglia, Wayne Hu, Hayato Motohashi
We study the dynamics of a spectator Higgs field which stochastically evolves during inflation onto near-critical trajectories on the edge of a runaway instability. We show that it…
Weakly-coupled stealth solution in scordatura degenerate theory
Hayato Motohashi, Shinji Mukohyama
In scalar-tensor theories we revisit the issue of strong coupling of perturbations around stealth solutions, i.e.\ backgrounds with the same forms of the metric as in General Relat…
Constant roll and primordial black holes
Hayato Motohashi, Shinji Mukohyama, Michele Oliosi
The constant-roll inflation with small positive value of the constant-roll parameter has been known to produce a slightly red-tilted cu…
Constant-roll inflation in scalar-tensor gravity
Hayato Motohashi, Alexei A. Starobinsky
We generalize the notion of constant-roll inflation earlier introduced in General Relativity (GR) and gravity to inflationary models in more general scalar-tensor gravity. A…
Linear stability analysis of hairy black holes in quadratic degenerate higher-order scalar-tensor theories: Odd-parity perturbations
Kazufumi Takahashi, Hayato Motohashi, Masato Minamitsuji
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 sub…
Exact black hole solutions in shift-symmetric quadratic degenerate higher-order scalar-tensor theories
Hayato Motohashi, Masato Minamitsuji
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 scal…