Analytic Structure of the Quark Propagator in a Model with an infrared vanishing Gluon Propagator

The Dyson-Schwinger equation for the quark self energy is solved in rainbow approximation using an infrared (IR) vanishing gluon propagator that introduces an IR mass scale $b$. There exists a $b$ dependent critical coupling indicating the spontaneous breakdown of chiral symmetry. If one chooses realistic QCD coupling constants the strength and the scale of spontaneous chiral symmetry breaking decouple from the IR scale for small $b$ while for large $b$ no dynamical chiral symmetry breaking occurs. At timelike momenta the quark propagator possesses a pole, at least for a large range of the parameter $b$. Therefore it is suggestive that quarks are not confined in this model for all values of $b$. Furthermore, we argue that the quark propagator is analytic within the whole complex momentum plane except on the timelike axis. Hence the na\"ıve Wick rotation is allowed.

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