Jaume Garriga

Gravity in the randall-sundrum brane world

We discuss the weak gravitational field created by isolated matter sources in the Randall-Sundrum brane world. For the case of a single wall of positive tension, the field stays localized near the wall if the source is stationary. We calculate the leading Kaluza-Klein corrections to the linearized gravitational field of a nonrelativistic spherical object, which is different from the Schwarzschild solution at large distances. In the case of two branes of opposite tension, linearized Brans-Dicke (BD) gravity is recovered on either wall, with different BD parameters. On the wall with positive tension the BD parameter is larger than 3000 provided that the separation between walls is larger than 4 times the AdS radius. The gravitational field due to shadow matter is also considered.

A note on accelerating cosmologies from compactifications and S-branes

We give a simple interpretation of the recent solutions for cosmologies with a transient accelerating phase obtained from compactification in hyperbolic manifolds, or from S-brane solutions of string/M-theory. In the four-dimensional picture, these solutions correspond to bouncing the radion field off its exponential potential. Acceleration occurs at the turning point, when the radion stops and the potential energy momentarily dominates. The virtues and limitations of these approaches become quite transparent in this interpretation.

Radion effective potential in the brane-world

We show that in brane-world scenarios with warped extra dimensions, the Casimir force due to bulk matter fields may be sufficient to stabilize the radion field φ. In particular, we calculate one loop effective potential for φ induced by bulk gravitons and other possible massless bulk fields in the Randall–Sundrum background. This potential has a local extremum, which can be a maximum or a minimum depending on the detailed bulk matter content. If the parameters of the background are chosen so that the hierarchy problem is solved geometrically, then the radion mass induced by Casimir corrections is hierarchically smaller than the TeV. Hence, in this important case, we must invoke an alternative mechanism (classical or nonperturbative) which gives the radion a sizable mass, to make it compatible with observations.

On likely values of the cosmological constant

We discuss models in which the smallness of the effective vacuum energy density

Transverse Fierz–Pauli symmetry

{\ensuremath{\rho}}_{\ensuremath{\Lambda}}

Many worlds in one

and the coincidence of the time of its dominance

A Stable hierarchy from Casimir forces and the holographic interpretation

{t}_{\ensuremath{\Lambda}}

Football shaped extra dimensions and the absence of self-tuning

with the epoch of galaxy formation

Anthropic Prediction for Λ and the Q Catastrophe

{t}_{G}

Cosmological constant and the time of its dominance

are due to anthropic selection effects. In such models, the probability distribution for