Roy Maartens
Institute of Cosmology & Gravitation
Portsmouth University
Portsmouth PO12EG
U.K.
email:
homepage:http://www.tech.port.ac.uk/staffweb/maartenr/
(Accepted on 29 April 2004)
(Published on 21 June 2004)
The observable
universe could be a -surface (the “brane”)
embedded in a
-dimensional spacetime
(the “bulk”), with Standard Model particles and fields trapped on the brane while gravity is free to
access the bulk. At least one of the
extra spatial dimensions could be very large
relative to the Planck scale, which lowers the fundamental
gravity scale, possibly even down to
the electroweak (
) level. This
revolutionary picture arises in
the framework of recent developments in M theory. The
-dimensional M theory encompasses the known
-dimensional superstring theories, and is
widely considered to be a
promising potential route to quantum gravity. General relativity
cannot describe gravity at high
enough energies and must be replaced by a quantum gravity theory,
picking up significant
corrections as the fundamental energy scale is approached. At low
energies, gravity is localized
at the brane and general relativity is recovered, but at high
energies gravity “leaks” into
the bulk, behaving in a truly higher-dimensional way. This
introduces significant changes
to gravitational dynamics and perturbations, with interesting and
potentially testable implications for high-energy astrophysics,
black holes, and cosmology. Brane-world models offer a phenomenological way to test some of the
novel predictions and corrections to general relativity
that are implied by M theory. This review discusses the geometry,
dynamics and perturbations of
simple brane-world models for cosmology and astrophysics, mainly
focusing on warped 5-dimensional
brane-worlds based on the Randall-Sundrum models.