Cosmological scaling solutions in generalised Gauss-Bonnet gravity theories

The conditions for the existence and stability of cosmological power-law scaling solutions are established when the Einstein-Hilbert action is modified by the inclusion of a function of the Gauss-Bonnet curvature invariant. The general form of the action that leads to such solutions is determined for the case where the universe is sourced by a barotropic perfect fluid. It is shown by employing an equivalence between the Gauss-Bonnet action and a scalar-tensor theory of gravity that the cosmological field equations can be written as a plane autonomous system. It is found that stable scaling solutions exist when the parameters of the model take appropriate values.Comment: 10 pages and 5 figure

f(R) theories

Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity - such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory and Gauss-Bonnet gravity, and address models that can satisfy both cosmological and local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in Relativity, Published version, Comments are welcom

Cosmic acceleration and phantom crossing in f(T)f(T)-gravity

In this paper, we propose two new models in $f(T)$ gravity to realize universe acceleration and phantom crossing due to dark torsion in the formalism. The model parameters are constrained and the observational test are discussed. The best fit results favors an accelerating universe with possible phantom crossing in the near past or future followed respectively by matter and radiation dominated era.Comment: 20 pages, 18 figures, Will appear in Astrophys Space Sc

Joufrois, roman français du XIIIe siècle, publié avec une introduction, un glossaire et des notes par Walter O. Streng-Renkonen, 1930. (Annales Universitatis Aboensis, Series B, t. XII)

Fay Percival B. Joufrois, roman français du XIIIe siècle, publié avec une introduction, un glossaire et des notes par Walter O. Streng-Renkonen, 1930. (Annales Universitatis Aboensis, Series B, t. XII). In: Romania, tome 58 n°229, 1932. pp. 114-120

Joufrois, roman français du XIIIe siècle, publié avec une introduction, un glossaire et des notes par Walter O. Streng-Renkonen, 1930. (Annales Universitatis Aboensis, Series B, t. XII)

Fay Percival B. Joufrois, roman français du XIIIe siècle, publié avec une introduction, un glossaire et des notes par Walter O. Streng-Renkonen, 1930. (Annales Universitatis Aboensis, Series B, t. XII). In: Romania, tome 58 n°229, 1932. pp. 114-120