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Extended mimetic gravity: Hamiltonian analysis and gradient instabilities
Kazufumi Takahashi, Tsutomu Kobayashi
We propose a novel class of degenerate higher-order scalar-tensor theories as an extension of mimetic gravity. By performing a noninvertible conformal transformation on "seed" scal…
Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations
Shin'ichi Hirano, Sakine Nishi, Tsutomu Kobayashi
We study the stability of a recently proposed model of scalar-field matter called mimetic dark matter or imperfect dark matter. It has been known that mimetic matter with higher de…
General invertible transformation and physical degrees of freedom
Kazufumi Takahashi, Hayato Motohashi, Teruaki Suyama +1
An invertible field transformation is such that the old field variables correspond one-to-one to the new variables. As such, one may think that two systems that are related by an i…
Generalized multi-Galileons, covariantized new terms, and the no-go theorem for non-singular cosmologies
Shingo Akama, Tsutomu Kobayashi
It has been pointed out that non-singular cosmological solutions in second-order scalar-tensor theories generically suffer from gradient instabilities. We extend this no-go result…