What does low energy physics tell us about the zero momentum gluon propagator

The connection between QCD, a nonlocal Nambu-Jona-Lasinio type model and the Landau gauge gluon propagator is explored. This two point function is parameterized by a functional form which is compatible with Dyson-Schwinger and lattice QCD results. Demanding the nonlocal model to reproduce the experimental values for the pion mass, the pion decay constant, Γπ→γγ and the light quark condensate we conclude that low energy physics does not distinguish between the so-called decoupling and scaling solutions of the Dyson-Schwinger equations. This result means that, provided that the model parameters are chosen appropriately, one is free to choose any of the above scenarios. Furthermore, the nonlocal Nambu-Jona-Lasinio quark model considered here is chiral invariant and satisfies the GMOR relation at the 1% level of precision.