On the Viability of a Non-Analytical f(R)-Theory

In this paper, we show how a power-law correction to the Einstein-Hilbert action provides a viable modified theory of gravity, passing the Solar-System tests, when the exponent is between the values 2 and 3. Then, we implement this paradigm on a cosmological setting outlining how the main phases of the Universe thermal history are properly reproduced. As a result, we find two distinct constraints on the characteristic length scale of the model, i.e., a lower bound from the Solar-System test and an upper one by guaranteeing the matter dominated Universe evolution.Comment: 9 pages, 2 figure

The Bianchi Classification of the Three-Dimensional Lie Algebras and Homogeneous Cosmologies and the Mixmaster Universe

The Bianchi classification of the three-dimensional Lie algebras and of the spatially homogeneous universes is presented in a rather pedagogical manner. The dynamics of the Bianchi-I, Bianchi-II and Bianchi-IX universes are discussed in detail. A special attention is paid to the phenomenon of the oscillatory approach to the cosmological singularity (BKL) known also as the Mixmaster universe. The stochasticity in cosmology and the connection between cosmological billiards and infinite-dimensional Lie algebras are briefly illustrated