  In this thesis I review cosmological and astrophysical exact models for
Randall-Sundrum-type braneworlds and their physical implications. I present new
insights and show their analogies with quantum theories via the holographic
idea. In astrophysics I study the two fundamental models of a spherically
symmetric static star and spherically symmetric collapsing objects. I show how
matching for the pressure of a static star encodes braneworld effects. In
addition I study the problem of the vacuum exterior conjecturing a uniqueness
theorem. Furthermore I show that a collapsing dust cloud in the braneworld has
a non-static exterior, in contrast to the General Relativistic case. This
non-static behaviour is linked to the presence of a "surplus potential energy"
that must be released, producing a non-zero flux of energy. Via holography this
can be connected with the Hawking process, giving an indirect measure of the
brane tension. In cosmology I investigate the generalization of the
Randall-Sundrum-type model obtained by introducing the Gauss-Bonnet combination
into the action. I elucidate the junction conditions necessary to study the
brane model and obtain the cosmological dynamics, showing that, even in the
thin shell limit for the brane, the Gauss-Bonnet term implies a non-trivial
internal structure for the matter and geometry distributions. Independently of
the gravitational theory used, I show how to derive the modified Friedman
equation and how it is related to the black hole solution of the theory. Via
holography I also show how to interpret quantum mechanically the mass of this
black hole from a four-dimensional perspective in the simplest
Randall-Sundrum-type scenario.
