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**Inflation and braneworlds.**
*(English)*
Zbl 1073.83051

Bretón, N. (ed.) et al., The early universe and observational cosmology. Papers from 5th Mexican school on gravitation and mathematical physics, Playa del Carmen, Quintana Roo, Mexico, November 24–29, 2002. Berlin: Springer (ISBN 3-540-21847-5/hbk). Lecture Notes in Physics 646, 357-379 (2004).

The Randall-Sundrum braneworld model [L. Randall and R. Sundrum, Phys. Rev. Lett. 83, No. 17, 3370–3373 (1999; Zbl 0946.81063), Phys. Rev. Lett. 83, No. 23, 4690–4693 (1999; Zbl 0946.81074)] supposes that our (four-dimensional) universe is a 3-brane or a domain wall like defect in a five-dimensional bulk space with anti-de Sitter (adS) geometry. This scenario is motivated from string theory, in particular, the so-called adS/CFT correspondence [J. Maldacena, Adv. Theor. Math. Phys. 2, 231–252 (1998; Zbl 0914.53047); E. Witten, Adv. Theor. Math. Phys. 2, 505–532 (1998; Zbl 1057.81550)] according to which a certain superstring theory on a five-dimensional adS space (times a compact space) is equivalent (i.e., dual) to a quantum field theory on a four-dimensional spacetime. The latter is the worldvolume of a 3-brane which is at a conformal boundary of the adS space.

The present review discusses cosmological issues in the context of the so called RS type II model (in which there is a single 3-brane in an adS bulk). The effect of gravity is felt differently in a braneworld model: e.g., there is an inverse-cube correction to Newton’s law at short distance. The Friedmann equation governing the cosmological evolution is also modified. The corrections are in the form of additional friction that can support a steeper inflaton potential compared to the standard scenario. The amplitude of density perturbations is also enhanced. However, the ratio of scalar to tensor perturbations, which being a good model independent parameter is a potential candidate to differentiate between models, turns out to be the same as in the standard scenario, to leading order. This approximation neglects the effect of the bulk on the evolution of the perturbations. Asymmetric braneworld models with different cosmological constants for the adS spaces on either sides of the brane are briefly discussed, as is the effect of a Gauss-Bonnet term.

For the entire collection see [Zbl 1051.83002].

The present review discusses cosmological issues in the context of the so called RS type II model (in which there is a single 3-brane in an adS bulk). The effect of gravity is felt differently in a braneworld model: e.g., there is an inverse-cube correction to Newton’s law at short distance. The Friedmann equation governing the cosmological evolution is also modified. The corrections are in the form of additional friction that can support a steeper inflaton potential compared to the standard scenario. The amplitude of density perturbations is also enhanced. However, the ratio of scalar to tensor perturbations, which being a good model independent parameter is a potential candidate to differentiate between models, turns out to be the same as in the standard scenario, to leading order. This approximation neglects the effect of the bulk on the evolution of the perturbations. Asymmetric braneworld models with different cosmological constants for the adS spaces on either sides of the brane are briefly discussed, as is the effect of a Gauss-Bonnet term.

For the entire collection see [Zbl 1051.83002].

Reviewer: D. Ghoshal (Allahabad)