Title of the Colloquium : Periodic Orbits, Localization in Normal Mode Space, and the Fermi-Pasta-Ulam Problem

Speaker : Dr. Sergej Flach, Max-Planck-Institut fuer Physik, Germany

Date: July 30, 2010 at 1500 hrs.

Venue: SINP Lecture Hall -II, Auditorium Complex

Abstract : I will discuss the Fermi-Pasta-Ulam (FPU) problem of non-equipartition of normal mode energies in a nonlinear chain, which is the first computational experiment known in literature. Non-equipartition is observed due to different time scales characterizing the mode-mode interaction, and finite available computational times. Exact periodic orbits are constructed, which are localized in normal mode space. The properties of these orbits largely dictate the dynamical outcome of the FPU experiment on the short time scales (which can be however very long). A discussion about the open problems in addressing the long time scale evolution is concluding the talk, together with a cross link to a recent hot topic of wave packet spreading in disordered nonlinear media.