ON ANALYTICAL SOLUTIONS OF f(R) MODIFIED GRAVITY THEORIES IN FLRW COSMOLOGIES

Stability of spherically symmetric solutions in modified theories of gravity

In recent years, a number of alternative theories of gravity have been proposed as possible resolutions of certain cosmological problems or as toy models for possible but heretofore unobserved effects. However, the implications of such theories for the stability structures such as stars have not been fully investigated. We use our “generalized variational principle”, described in a previous wor...

Homogeneous cosmologies in generalized modified gravity

Dynamical system methods are used in the study of the stability of spatially flat homogeneous cosmologies within a large class of generalized modified gravity models in the presence of a relativistic matter-radiation fluid. The present approach can be considered as the generalization of previous works in which only F (R) cases were considered. Models described by an arbitrary function of all po...

On IR solutions in Horava gravity theories

In this note we search for large distance solutions of Horava gravity. In the case of the ”detailed balance” action, gravity solutions asymptote to IR only above the cosmological constant (∼horizon) scale. However, if one adds IR dominant terms αR(3) + βΛW , one can recover general relativity solutions on usual scales in the real Universe, provided one fine-tunes the cosmological constant, reob...

Introduction to Palatini Theories of Gravity and Nonsingular Cosmologies

Flrw Universes from “wave-like” Cosmologies in 5d

We consider the evolution of a 4D-universe embedded in a five-dimensional (bulk) world with a large extra dimension and a cosmological constant. The cosmology in 5D possesses “wave-like” character in the sense that the metric coefficients in the bulk are functions of the extra coordinate and time in a way similar to a pulse or traveling wave propagating along the fifth dimension. This assumptio...