Both the right and left eigenfunctions and eigenvalues of the linearized
homogeneous Boltzmann equation for inelastic Maxwell molecules corresponding to
the hydrodynamic modes are calculated. Also, some non-hydrodynamic modes are
identified. It is shown that below a critical value of the parameter
characterizing the inelasticity, one of the kinetic modes decays slower than
one of the hydrodynamic ones. As a consequence, a closed hydrodynamic
description does not exist in that regime. Some implications of this behavior
on the formally computed Navier-Stokes transport coefficients are discussed.Comment: Submitted to PRL (13/04/10
