Littlewood problem for a singular subquadratic potential

Abstract

We consider a periodically forced singular oscillator in which the potential has subquadratic growth at infinity and admits a singularity.Using Moser's twist theorem of invariant curves, we show the existence of quasiperiodic solutions. This solves the Littlewood problem on the boundedness of all solutions for such a system. © Springer Science+Business Media New York 2013.