Résumé:
The work presented in this thesis is devoted to the study of the existence and multiplicity
positive non-trivial solutions of a fractional p-Laplacian problem. The results are obtained
using some variational techniques. The first result is that of the existence of two non-trivial
positive solutions, using the Nehari manifold and the fibering method, in the critical and
subcritical cases. The second result contains the existence of three distinct solutions, only in
the critical case, using Ekeland’s variational principle, under different assumptions.