LANDAU POLE SCREENING IN THE GROSS-NEVEU MODEL - 1 N VERSUS OPERATOR PRODUCT EXPANSION/

In asymptotically free theories, Landau poles at low energy scales lim it the range of validity of perturbative predictions. Taking into acco unt non-perturbative corrections in an operator product expansion (OPE ) does not alleviate this problem, however, non-vanishing condensates are believed to prevent the singularities from producing unphysical (t achyonic) poles in Green's functions. We illustrate the mechanism of L andau pole screening by dynamically generated condensates in the Gross -Neveu model, in which a dynamical fermion mass and a scalar boundstat e are formed. In the large N limit the pertinent Green's function is a n entirely smooth function of the Euclidean momentum transfer. We demo nstrate that its asymptotic behaviour nevertheless resembles the renor malisation group improved perturbative result accompanied by OPE corre ctions for momenta well above the Landau pole. The 1/N expansion is su ited to account for non-trivial ground state correlations beyond the r ange of validity of OPE predictions.