M. Berti, L. Biasco
Vibrations
with nonmonotone forcing terms
(127K, latex)

ABSTRACT.  We prove existence and regularity of periodic in time solutions of
completely resonant nonlinear forced wave equations with Dirichlet
boundary conditions for a large class of non-monotone
forcing terms.
Our approach is based on
a variational Lyapunov-Schmidt reduction.
It turns out that the infinite dimensional
bifurcation equation exhibits an intrinsic
lack of compactness.
We solve it via a minimization argument
and a-priori estimate methods inspired to regularity theory of
[R67]