Violation of Quantum Gauge Invariance in Georgi-Glashow SU(5)
  We check whether the SU(5) model, originally suggested by Georgi and Glashow, is compatible with perturbative quantum gauge invariance in first and second order for massive asymptotic gauge fields. We see that this is not the case: the SU(5) grand unified model does not meet with our restrictions from second order gauge invariance. 
Martin Ambauen, Gunter Scharf