Thermodynamics of a Fermi liquid beyond the low-energy limit

We consider the non-analytic temperature dependences of the specific heat coefficient, C(T)/T, and spin susceptibility, \chi_{s} (T), of 2D interacting fermions beyond the weak-coupling limit. We demonstrate within the Luttinger-Ward formalism that the leading temperature dependences of C(T)/T and \chi_s (T) are linear in T, and are described by the Fermi liquid theory. We show that these temperature dependences are universally determined by the states near the Fermi level and, for a generic interaction, are expressed via the spin and charge components of the exact backscattering amplitude of quasi-particles. We compare our theory to recent experiments on monolayers of 3He.