6.3k citations
Counting papers with at most 25 authors, so collaboration author lists do not stand in for the people here.
- Kyoto UniversityJP16 papers
- Tokyo Institute of TechnologyJP10 papers
- Inter-University Centre for Astronomy and AstrophysicsIN9 papers
- The University of TokyoJP9 papers
- Jamia Millia IslamiaIN8 papers
- Özyeğin UniversityTR8 papers
- Yukawa Institute for Theoretical PhysicsJP8 papers
- Advanced Science Research CenterJP7 papers
- Japan Atomic Energy AgencyJP7 papers
- Astronomical Observatory of RomeIT6 papers
- The University of OsakaJP5 papers
- Jožef Stefan InstituteSI4 papers
18 papers · 1 filter
Constraints on scalar-tensor models of dark energy from observational and local gravity tests
Shinji Tsujikawa, Kotub Uddin, Shuntaro Mizuno +2
We construct a family of viable scalar-tensor models of dark energy (DE) which possess a phase of late-time acceleration preceded by a standard matter era, while at the same time s…
Density perturbations in f(R) gravity theories in metric and Palatini formalisms
Shinji Tsujikawa, Kotub Uddin, Reza Tavakol
We make a detailed study of matter density perturbations in both metric and Palatini formalisms in theories whose Lagrangian density is a general function, f(R), of the Ricci scala…
Observational signatures of f(R) dark energy models that satisfy cosmological and local gravity constraints
Shinji Tsujikawa
We discuss observational consequences of f(R) dark energy scenarios that satisfy local gravity constraints (LGC) as well as conditions of the cosmological viability. The model we s…
Matter density perturbations and effective gravitational constant in modified gravity models of dark energy
Shinji Tsujikawa
We derive the equation of matter density perturbations on sub-horizon scales for a general Lagrangian density f(R, phi, X) that is a function of a Ricci scalar R, a scalar field ph…
Phantom crossing, equation-of-state singularities, and local gravity constraints in f(R) models
Luca Amendola, Shinji Tsujikawa
We identify the class of f(R) dark energy models which have a viable cosmology, i.e. a matter dominated epoch followed by a late-time acceleration. The deviation from a LambdaCDM m…
Probing the Coupling between Dark Components of the Universe
Zong-Kuan Guo, Nobuyoshi Ohta, Shinji Tsujikawa
We place observational constraints on a coupling between dark energy and dark matter by using 71 Type Ia supernovae (SNe Ia) from the first year of the five-year Supernova Legacy S…
f(R) gravity theories in Palatini formalism: cosmological dynamics and observational constraints
Stephane Fay, Reza Tavakol, Shinji Tsujikawa
We make a systematic study of the cosmological dynamics for a number of f(R) gravity theories in Palatini formalism. We find a number of interesting results: (i) models based on th…
Challenges for scaling cosmologies
Luca Amendola, Miguel Quartin, Shinji Tsujikawa +1
A cosmological model that aims at solving the coincidence problem should show that dark energy and dark matter follow the same scaling solution from some time onward. At the same t…
Power-laws f(R) theories are cosmologically unacceptable
Luca Amendola, David Polarski, Shinji Tsujikawa
In a recent paper [1] (PRL 98,131302,2007) we have shown that f(R)=R + mu R^{n} modified gravity dark energy models are not cosmologically viable because during the matter era that…
Are f(R) dark energy models cosmologically viable ?
Luca Amendola, David Polarski, Shinji Tsujikawa
All modified gravity theories are conformally identical to models of quintessence in which matter is coupled to dark energy with a strong coupling. This coupling induces a c…
Reconstruction of general scalar-field dark energy models
Shinji Tsujikawa
The reconstruction of scalar-field dark energy models is studied for a general Lagrangian density , where is a kinematic term of a scalar field . We implement the c…
Dynamics of assisted quintessence
Soo A Kim, Andrew R Liddle, Shinji Tsujikawa
We explore the dynamics of assisted quintessence, where more than one scalar field is present with the same potential. For potentials with tracking solutions, the fields naturally…
Inflation Dynamics and Reheating
Bruce A. Bassett, Shinji Tsujikawa, David Wands
We review the theory of inflation with single and multiple fields paying particular attention to the dynamics of adiabatic and entropy/isocurvature perturbations which provide the…
Phantom damping of matter perturbations
Luca Amendola, Shinji Tsujikawa, M. Sami
Cosmological scaling solutions are particularly important in solving the coincidence problem of dark energy. We derive the equations of sub-Hubble linear matter perturbations for a…
Flow equations in generalized braneworld scenarios
Gianluca Calcagni, Andrew R. Liddle, Erandy Ramirez
We discuss the flow equations in the context of general braneworld cosmologies with a modified Friedmann equation, for either an ordinary scalar field or a Dirac-Born-Infeld tachyo…
Testing for double inflation with WMAP
David Parkinson, Shinji Tsujikawa, Bruce A. Bassett +1
With the WMAP data we can now begin to test realistic models of inflation involving multiple scalar fields. These naturally lead to correlated adiabatic and isocurvature (entropy)…
Observational constraints on patch inflation in noncommutative spacetime
Gianluca Calcagni, Shinji Tsujikawa
We study constraints on a number of patch inflationary models in noncommutative spacetime using a compilation of recent high-precision observational data. In particular, the four-d…
Observational constraints on braneworld inflation: the effect of a Gauss-Bonnet term
Shinji Tsujikawa, M. Sami, Roy Maartens
High-energy modifications to general relativity introduce changes to the perturbations generated during inflation, and the latest high-precision cosmological data can be used to pl…