90 citations · 276 across the 9 of their papers we have counts for
9 papers
Boundary Conditions for Constraint Systems in Variational Principle
Keisuke Izumi, Keigo Shimada, Kyosuke Tomonari +1
We show the well-posed variational principle in constraint systems. In a naive procedure of the variational principle with constraints, the proper number of boundary conditions doe…
Mimetic K-essence
Pavel Jiroušek, Keigo Shimada, Alexander Vikman +1
We propose a new non-trivial way to combine mimetic dark matter with the mimetic formulation of unimodular gravity. This yields a Weyl-invariant higher-derivative scalar-vector-ten…
New Dynamical Degrees of Freedom from Invertible Transformations
Pavel Jiroušek, Keigo Shimada, Alexander Vikman +1
We show that invertible transformations of dynamical variables can change the number of dynamical degrees of freedom. Moreover, even in cases when the number of dynamical degrees o…
Disforming to Conformal Symmetry
Pavel Jiroušek, Keigo Shimada, Alexander Vikman +1
We analyse the dynamical properties of disformally transformed theories of gravity. We show that disformal transformation typically introduces novel degrees of freedom, equivalent…
Losing the trace to find dynamical Newton or Planck constants
Pavel Jiroušek, Keigo Shimada, Alexander Vikman +1
We show that promoting the trace part of the Einstein equations to a trivial identity results in the Newton constant being an integration constant. Thus, in this formulation the Ne…
Cosmological Perturbations in Palatini Formalism
Mio Kubota, Kin-ya Oda, Keigo Shimada +1
We investigate cosmological perturbations of scalar-tensor theories in Palatini formalism. First we introduce an action where the Ricci scalar is conformally coupled to a function…
Scalar-metric-affine theories: Can we get ghost-free theories from symmetry?
Katsuki Aoki, Keigo Shimada
We reveal the existence of a certain hidden symmetry in general ghost-free scalar-tensor theories which can only be seen when generalizing the geometry of the spacetime from Rieman…
Metric-affine Gravity and Inflation
Keigo Shimada, Katsuki Aoki, Kei-ichi Maeda
We classify the metric-affine theories of gravitation, in which the metric and the connections are treated as independent variables, by use of several constraints on the connection…
Galileon and generalized Galileon with projective invariance in a metric-affine formalism
Katsuki Aoki, Keigo Shimada
We study scalar-tensor theories respecting the projective invariance in the metric-affine formalism. The metric-affine formalism is a formulation of gravitational theories such tha…