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Conditions for the cosmological viability of f(R) dark energy models
Luca Amendola, Radouane Gannouji, David Polarski +1
We derive the conditions under which dark energy models whose Lagrangian densities f are written in terms of the Ricci scalar R are cosmologically viable. We show that the cosmolog…
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…
Avoidance of future singularities in loop quantum cosmology
M. Sami, Parampreet Singh, Shinji Tsujikawa
We consider the fate of future singularities in the effective dynamics of loop quantum cosmology. Non-perturbative quantum geometric effects which lead to modification of the…
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…