  This PhD thesis discusses the internal structure of topological defects, and
branes in extra-dimensions, carrying fermionic currents.
  The general framework in which these objects may appear is presented in the
first part while the second part is devoted to the dynamic of cosmic strings, a
class of topological defects of uttermost importance to modern cosmology, as it
can be obtained from a macroscopic covariant formalism. This formalism offers a
unified description of cosmic strings, including the case for which they carry
internal currents, and allows the study of their cosmological evolution, and
implications, by means of numerical simulations. Its validity has already been
confirmed for cosmic string carrying bosonic currents, and the third part
provides new results concerning the fermionic currents case. First, the fermion
mass spectrum in a cosmic string is computed, and suggests that fermionic
currents are usually built on massive propagation modes leading to a new
equation of state. This highlights that the usual one parameter macroscopic
formalism is not always sufficient in case of fermionic currents. Moreover,
contrary to the bosonic case, the dynamics stemming from this equation of state
exhibits transitions between the subsonic and supersonic regimes whose
consequences in cosmology could be important. The last part is an extension of
these results to brane cosmology for which our universe is viewed as a four
dimensional domain wall embedded in a five dimensional space-time. In the
framework of the Randall-Sundrum model, the masses of the trapped fermions on
the brane can be predicted.
