3.9k citations · 23.3k across the 206 of their papers we have counts for
39 papers · 1 filter
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}…
Instabilities in Horndeski Yang-Mills inflation
Jose Beltran Jimenez, Lavinia Heisenberg, Ryotaro Kase +2
A non-abelian gauge field with a non-minimal Horndeski coupling to gravity gives rise to a de Sitter solution followed by a graceful exit to a radiation-dominated epoch. In…
Cosmic microwave background and inflation in multi-fractional spacetimes
Gianluca Calcagni, Sachiko Kuroyanagi, Shinji Tsujikawa
We use FIRAS and Planck 2015 data to place observational bounds on inflationary scenarios in multi-fractional spacetimes with -derivatives. While a power-law expansion in the ge…
Beyond generalized Proca theories
Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa
We consider higher-order derivative interactions beyond second-order generalized Proca theories that propagate only the three desired polarizations of a massive vector field beside…
Disformal invariance of cosmological perturbations in a generalized class of Horndeski theories
Shinji Tsujikawa
It is known that Horndeski theories can be transformed to a sub-class of Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories under the disformal transformation of the metric $g_{μν} \…
Inflationary gravitational waves in the effective field theory of modified gravity
Antonio De Felice, Shinji Tsujikawa
In the approach of the effective field theory of modified gravity, we derive the second-order action and the equation of motion for tensor perturbations on the flat isotropic cosmo…
Effective field theory approach to modified gravity including Horndeski theory and Hořava-Lifshitz gravity
Ryotaro Kase, Shinji Tsujikawa
We review the effective field theory of modified gravity in which the Lagrangian involves three dimensional geometric quantities appearing in the 3+1 decomposition of space-time. O…
Cosmology in generalized Horndeski theories with second-order equations of motion
Ryotaro Kase, Shinji Tsujikawa
We study the cosmology of an extended version of Horndeski theories with second-order equations of motion on the flat Friedmann-Lemaître-Robertson-Walker (FLRW) background. In addi…
Effective field theory of modified gravity on the spherically symmetric background: leading order dynamics and the odd-type perturbations
Ryotaro Kase, László Árpád Gergely, Shinji Tsujikawa
We consider perturbations of a static and spherically symmetric background endowed with a metric tensor and a scalar field in the framework of the effective field theory of modifie…
Effective field theory of modified gravity with two scalar fields: dark energy and dark matter
László Á. Gergely, Shinji Tsujikawa
We present a framework for discussing the cosmology of dark energy and dark matter based on two scalar degrees of freedom. An effective field theory of cosmological perturbations i…
Anisotropic power-law k-inflation
Junko Ohashi, Jiro Soda, Shinji Tsujikawa
It is known that power-law k-inflation can be realized for the Lagrangian , where is the kinetic energy of a scalar field and is an arbitrary…
Super-renormalizable or finite completion of the Starobinsky theory
Fabio Briscese, Leonardo Modesto, Shinji Tsujikawa
The recent Planck data of Cosmic Microwave Background (CMB) temperature anisotropies support the Starobinsky theory in which the quadratic Ricci scalar drives cosmic inflation. We…
Non-local massive gravity
Leonardo Modesto, Shinji Tsujikawa
We present a general covariant action for massive gravity merging together a class of "non-polynomial" and super-renormalizable or finite theories of gravity with the non-local the…
Shapes of primordial non-Gaussianities in the Horndeski's most general scalar-tensor theories
Antonio De Felice, Shinji Tsujikawa
In the Horndeski's most general scalar-tensor theories, we derive the three-point correlation function of scalar non-Gaussianities generated during single-field inflation in the pr…
Consistency of inflation and preheating in F(R) supergravity
Sergei V. Ketov, Shinji Tsujikawa
We study inflation and preheating in F(R) supergravity characterized by two mass scales of a scalar degree of freedom (scalaron): M (associated with the inflationary era) and m (as…
Generalized Galileon cosmology
Antonio De Felice, Shinji Tsujikawa
We study the cosmology of a generalized Galileon field with five covariant Lagrangians in which is replaced by general scalar functions (i=1,...,5). For these th…
Solar system constraints on f(G) gravity models
Antonio De Felice, Shinji Tsujikawa
We discuss solar system constraints on f(G) gravity models, where f is a function of the Gauss-Bonnet term G. We focus on cosmologically viable f(G) models that can be responsible…
Construction of cosmologically viable f(G) gravity models
Antonio De Felice, Shinji Tsujikawa
We derive conditions under which f(G) gravity models, whose Lagrangian densities f are written in terms of a Gauss-Bonnet term G, are cosmologically viable. The most crucial condit…
Prospects of inflation in delicate D-brane cosmology
Sudhakar Panda, M. Sami, Shinji Tsujikawa
We study D-brane inflation in a warped conifold background that includes brane-position dependent corrections for the nonperturbative superpotential. Instead of stabilizing the vol…
UV stable, Lorentz-violating dark energy with transient phantom era
Maxim Libanov, Eleftherios Papantonopoulos, Valery Rubakov +2
Phantom fields with negative kinetic energy are often plagued by the vacuum quantum instability in the ultraviolet region. We present a Lorentz-violating dark energy model free fro…
Realizing Scale-invariant Density Perturbations in Low-energy Effective String Theory
Zong-Kuan Guo, Nobuyoshi Ohta, Shinji Tsujikawa
We discuss the realization of inflation and resulting cosmological perturbations in the low-energy effective string theory. In order to obtain nearly scale-invariant spectra of den…
String-inspired cosmology: Late time transition from scaling matter era to dark energy universe caused by a Gauss-Bonnet coupling
Shinji Tsujikawa, M. Sami
The Gauss-Bonnet (GB) curvature invariant coupled to a scalar field can lead to an exit from a scaling matter-dominated epoch to a late-time accelerated expansion, which is att…
General analytic formulae for attractor solutions of scalar-field dark energy models and their multi-field generalizations
Shinji Tsujikawa
We study general properties of attractors for scalar-field dark energy scenarios which possess cosmological scaling solutions. In all such models there exists a scalar-field domina…
Inflation from D3-brane motion in the background of D5-branes
Sudhakar Panda, M. Sami, Shinji Tsujikawa +1
We study inflation arising from the motion of a BPS D3-brane in the background of a stack of k parallel D5-branes. There are two scalar fields in this set up-- (i) the radion field…