Renormalizable W Self-Energy in the Unitary Gauge via the Pinch   Technique
  We use the S-matrix pinch technique to derive to one loop order an effective renormalizable self-energy for the W gauge boson, when the theory is quantized in the unitary gauge. We then show that this amplitude is identical to the $\xi$-independent W self-energy previously constructed by applying the pinch technique in the context of the renormalizable $R_{\xi}$ gauges.} 
Joannis Papavassiliou and Alberto Sirlin