NONLINEAR RESPONSE THEORY IN DAMPED MATHIEUS SYSTEM

A response theory for dissipative systems, which are driven by an exte rnal periodic field, is proposed. The propagator of the system is deco mposed into the periodic factor with the same frequency as the externa l field and the remaining factor. The relation between the usual Floqu et exponent and the remaining factor is studied. It is shown that the remaining factor is responsible for the appearance of subharmonics. Da mped Mathieu's equation is studied as an application of the general th eory.