Sante Carloni

Cosmological dynamics of R**n gravity

A detailed analysis of dynamics of cosmological models based on Rn gravity is presented. We show that the cosmological equations can be written as a first-order autonomous system and analysed using the standard techniques of dynamical system theory. In the absence of perfect fluid matter, we find exact solutions whose behaviour and stability are analysed in terms of the values of the parameter n. When matter is introduced, the nature of the (non-minimal) coupling between matter and higher order gravity induces restrictions on the allowed values of n. Selecting such intervals of values and following the same procedure used in the vacuum case, we present exact solutions and analyse their stability for a generic value of the parameter n. From this analysis emerges the result that for a large set of initial conditions an accelerated expansion is an attractor for the evolution of the Rn cosmology. When matter is considered a transient almost-Friedman phase can also be present before the transition to accelerated expansion.

New framework for studying spherically symmetric static solutions in f (R) gravity

We develop a new covariant formalism to treat spherically symmetric spacetimes in metric f(R) theories of gravity. Using this formalism we derive the general equations for a static and spherically symmetric metric in a general f(R) gravity. These equations are used to determine the conditions for which the Schwarzschild metric is the only vacuum solution with vanishing Ricci scalar. We also show that our general framework provides a clear way of showing that the Schwarzschild solution is not a unique static spherically symmetric solution, providing some insight into how the current form of Birkhoffs theorem breaks down for these theories.

Solar system constraints on Rindler acceleration

We discuss the classical tests of general relativity in the presence of Rindler acceleration. Among these tests the perihelion shifts give the tightest constraints and indicate that the Pioneer anomaly cannot be caused by a universal solar system Rindler acceleration. We address potential caveats for massive test-objects. Our tightest bound on Rindler acceleration that comes with no caveats is derived from radar echo delay and yields |a|<3nm/s^2.

Dynamical system analysis for a nonminimal torsion-matter coupled gravity

Centro Multidisciplinar de Astrofisica - CENTRA Instituto Superior Tecnico IST Universidade de Lisboa-UL, Avenida Rovisco Pais 1

On dynamical systems approaches and methods in

We discuss dynamical systems approaches and methods applied to flat Robertson-Walker models in

f(R)

f(R)

cosmology

-gravity. We argue that a complete description of the solution space of a model requires a global state space analysis that motivates globally covering state space adapted variables. This is shown explicitly by an illustrative example,

An analysis of the phase space of Hořava-Lifshitz cosmologies

f(R) = R + \alpha R^2

Geometrical approach to strong gravitational lensing in f(R) gravity

,

Conformal transformations in cosmology of modified gravity: the covariant approach perspective

\alpha > 0