Bounds on the decay of correlations for lambda(Δphi)4 models

We consider models, with an abelian continuous group of symmetry. We generalize Brascamp-Lieb inequalities to get (lambda-independent) bounds on the low momentum behaviour of general correlation functions when these are truncated into two clusters. We then use this result to derive an asymptotic expansion (up the second order in lambda) of the dielectric constant of this system. (orig./HPOE)