Periodic solutions to second order nonautonomous differential systems with unbounded nonlinearities

Abstract

Key words Second order system, Ahmad-Lazer-Paul type condition, saddle point theorem MSC (2010) 58F22We investigate the existence of periodic solutions of differential systems with a skew-symmetric matrix term and unbounded nonlinearities. Under new generalized Ahmad-Lazer-Paul conditions, some existence results are obtained and some results in the literature are improved.