3,683 research outputs found
Black holes in extended gravity theories in Palatini formalism
We consider several physical scenarios where black holes within classical
gravity theories including and Ricci-squared corrections and formulated
\`a la Palatini can be analytically studied.Comment: 4 pages, contribution to the "Spanish Relativity Meeting in Portugal
2012 (Progress in Mathematical Relativity, Gravitation and Cosmology)",
Springer Proceedings in Mathematics (to appear
Palatini approach to bouncing cosmologies and DSR-like effects
It is shown that a quadratic gravitational Lagrangian in the Palatini
formulation is able to capture different aspects of quantum gravity
phenomenology in a single framework. In particular, in this theory field
excitations propagating with different energy-densities perceive different
background metrics, a fundamental characteristic of the DSR and Rainbow Gravity
approaches. This theory, however, avoids the so-called soccer ball problem.
Also, the resulting isotropic and anisotropic cosmologies are free from the big
bang singularity. This singularity avoidance occurs non-perturbatively and
shares some similitudes with the effective dynamics of loop quantum cosmology.Comment: 4 pages. Proceedings of Loops'11, Madrid. To appear in Journal of
Physics: Conference Series (JPCS
The gravity lagrangian according to solar system experiments
In this work we show that the gravity lagrangian f(R) at relatively low
curvatures in both metric and Palatini formalisms is a bounded function that
can only depart from the linearity within the limits defined by well known
functions. We obtain those functions by analysing a set of inequalities that
any f(R) theory must satisfy in order to be compatible with laboratory and
solar system observational constraints. This result implies that the recently
suggested f(R) gravity theories with nonlinear terms that dominate at low
curvatures are incompatible with observations and, therefore, cannot represent
a valid mechanism to justify the cosmic speed-up.Comment: 4 pages, revtex
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