Differential geometry, Palatini gravity and reduction

Hybrid Metric-Palatini Gravity

Recently, the phenomenology of f(R) gravity has been scrutinized. This scrutiny has been motivated by the possibility to account for the self-accelerated cosmic expansion without invoking dark energy sources. Besides, this kind of modified gravity is capable of addressing the dynamics of several self-gravitating systems alternatively to the presence of dark matter. It has been established that ...

Palatini Actions and Quantum Gravity Phenomenology

We show that an invariant an universal length scale can be consistently introduced in a generally covariant theory through the gravitational sector using the Palatini approach. The resulting theory is able to capture different aspects of quantum gravity phenomenology in a single framework. In particular, it is found that in this theory field excitations propagating with different energy-densiti...

Bouncing cosmologies in Palatini fðRÞ gravity

Hèlios Sanchis-Alepuz Departamento de Fı́sica Teórica and IFIC, Centro Mixto Universidad de Valencia-CSIC. Facultad de Fı́sica, Universidad de Valencia, Burjassot-46100, Valencia, Spain and Fachbereich Theoretische Physik, Institut für Physik, Karl-Franzens-Universität Graz, Universitätsplatz 5, A-8010 Graz, Austria (Received 12 June 2009; published 16 July 2009) We consider the early time cosmol...

Isotropic and Anisotropic Bouncing Cosmologies in Palatini Gravity

We study isotropic and anisotropic (Bianchi I) cosmologies in Palatini f(R) and f(R,RμνR μν) theories of gravity and consider the existence of non-singular bouncing solutions in the early universe. We find that all f(R) models with isotropic bouncing solutions develop shear singularities in the anisotropic case. On the contrary, the simple quadratic model R+ aR/RP +RμνR /RP exhibits regular bou...

Introduction to Palatini Theories of Gravity and Nonsingular Cosmologies