219 citations · 2.3k across the 55 of their papers we have counts for
7 papers · 1 filter
Weak cosmic growth in coupled dark energy with a Lagrangian formulation
Ryotaro Kase, Shinji Tsujikawa
We investigate a dark energy scenario in which a canonical scalar field is coupled to the four velocity of cold dark matter (CDM) through a derivative interaction $u_…
Scalar-field dark energy nonminimally and kinetically coupled to dark matter
Ryotaro Kase, Shinji Tsujikawa
We provide a general framework for studying the dark energy cosmology in which a scalar field is nonminimally and kinetically coupled to Cold Dark Matter (CDM). The scalar-grav…
Coupled vector dark energy
Shintaro Nakamura, Ryotaro Kase, Shinji Tsujikawa
We provide a general framework for studying the evolution of background and cosmological perturbations in the presence of a vector field coupled to cold dark matter (CDM). We…
Neutron stars in gravity and scalar-tensor theories
Ryotaro Kase, Shinji Tsujikawa
In gravity and Brans-Dicke theory with scalar potentials, we study the structure of neutron stars on a spherically symmetric and static background for two equations of state…
Anisotropic -form dark energy
Juan P. Beltrán Almeida, Alejandro Guarnizo, Ryotaro Kase +2
We study the dynamics of dark energy in the presence of a 2-form field coupled to a canonical scalar field . We consider the coupling proportional to $e^{-μϕ/M_{\rm pl}} H_{αβγ}…
Tracker and scaling solutions in DHOST theories
Noemi Frusciante, Ryotaro Kase, Kazuya Koyama +2
In quadratic-order degenerate higher-order scalar-tensor (DHOST) theories compatible with gravitational-wave constraints, we derive the most general Lagrangian allowing for tracker…