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On a subtle point of sum rules calculations: toy model
We consider a two-point correlator in massless model within the
ladder approximation . The spectral density of the correlator is known
explicitly and does not contain any resonances. Meanwhile making use of the
standard sum rules technique with a simple "resonance + continuum" model of the
spectrum allows to predict parameters of the "resonance" very accurately in the
sense that all necessary criteria of stability are perfectly satisfied.Comment: LaTeX fil
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