The Quasi-Infra-Red Fixed Point at Higher Loops
  We calculate the four-loop $\beta$-function for the generalised Wess-Zumino model. We use the result and Pad\'e-Borel summation to discuss the domain of attraction of the quasi-infra-red fixed point of the top-quark Yukawa coupling in the supersymmetric standard model, and argue that the domain is in fact substantial. 
P.M. Ferreira, I. Jack and D.R.T. Jones