On the periodic solutions of perturbed 4D non-resonant systems

Agraïments: The second author is partially supported by a FAPESP-BRAZIL grant 2012/10231-7. The third author is partially supported by a FAPESP-BRAZIL grant 2007/06896-5. The first and third authors are also supported by the joint project CAPES-MECD grant PHB-2009-0025-PC.We provide sufficient conditions for the existence of periodic solutions of a 4D non-resonant system perturbed by smooth or non-smooth functions. We apply these results to study the small amplitude periodic solutions of the non-linear planar double pendulum perturbed by smooth or non-smooth function