Exponential return to equilibrium for hypoelliptic quadratic systems
  We study the problem of convergence to equilibrium for evolution equations associated to general quadratic operators. Quadratic operators are non-selfadjoint differential operators with complex-valued quadratic symbols. Under appropriate assumptions, a complete description of the spectrum of such operators is given and the exponential return to equilibrium with sharp estimates on the rate of convergence is proven. Some applications to the study of chains of oscillators and the generalized Langevin equation are given. 
M. Ottobre, G.A. Pavliotis, K. Pravda-Starov
math-ph math.MP math.SP