Atypical bifurcation for periodic solutions of φ -Laplacian systems

In this paper, we study the T-periodic solutions of the parameter-dependent \phi-Laplacian equation \begin{equation*} (\phi(x'))'=F(\lambda,t,x,x'). \end{equation*} Based on the topological degree theory, we present some atypical bifurcation results in the sense of Prodi-Ambrosetti, i.e., bifurcation of T-periodic solutions from \lambda=0. Finally, we propose some applications to Liénard-type equations.