Improved Hartree--Fock resummations and spontaneous symmetry breaking release_rev_6f5a8669-4e1d-46df-adbc-a317c17bef10

Abstract

The standard Hartree--Fock approximation of the O(N)-invariant ϕ^4 model suffers from serious renormalization problems. In addition, when the symmetry is spontaneously broken, another shortcoming appears in relation to the Goldstone bosons: they fail to be massless in the intermediate states. In this work, within the framework of out--of--equilibrium Quantum Field Theory, we propose a class of systematic improvements of the Hartree--Fock resummation which overcomes all the above mentioned difficulties while ensuring also exact Renormalization--Group invariance to one loop.
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