  This thesis is essentially organized in two parts: braneworlds and higher
dimensional black objects with a cosmological constant. We present solitonic
braneworld models where the brane are inflating and with the presence of a
cosmological constant, by analyzing four particular models. These models,
although slightly different exhibit common features which are pointed out. We
also consider $1+1$ dimensional toy models for coupling fermionic matter fields
to braneworld. In particular, we focus on a kink or kink/anti-kink solution of
the Sine-Gordon model, which can be seen as modeling a brane in the dimensions
transverse to our four dimensional spacetime. We also analyze the stability of
three particular models admitting kink or anti-kink like solutions and show
that the stability equations are Poschl-Teller equations. In the second part
after quickly reviewing available analytically known solutions, we present the
numerical construction of the higher dimensional charged rotating black hole
with a cosmological constant. Then, we present the black string solution and
review the stability problem of the latter before investigating the existence
of a de Sitter black string, which turns out not to be regular. Finally, we
present the AdS counterpart of the black string solution and study its
stability. Then, we construct numerically non uniform black strings, first in a
perturbative approach, then in the full non linear regime. Our result suggest
the existence of a thermodynamically stable phase of non uniform black string
and point to the presence of a phase of AdS localized black hole. Moreover, we
argue that the phase transition from uniform to non uniform black strings can
be of order larger than one in any number of dimensions, which is not the case
without a cosmological constant.
