Truncation schemes in the SDE approach to non-perturbative studies often break symmetries of the Lagrangian of the theory, and so one attempts to construct improved vertex ansatze that better preserve them. Using strongly coupling QED as a prototype field theory, we show how one may apply multiplicative renormalisability to further constrain the fermion-vector boson vertex of unquenched QED, and give explicit numerical calculations. Following this, we examine the chiral condensates dependence upon the current quark mass in three models of QCD, via the Schwinger-Dyson equations, with the aim of determining the ss-bar condensate so necessary an input for QCD sum rules.
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