A Manifestly Gauge Invariant, Continuum Calculation of the SU(N)   Yang-Mills two-loop beta function
  The manifestly gauge invariant Exact Renormalisation Group provides a framework for performing continuum computations in SU(N) Yang-Mills theory, without fixing the gauge. We use this formalism to compute the two-loop beta function in a manifestly gauge invariant way, and without specifying the details of the regularisation scheme. 
Tim R. Morris and Oliver J.Rosten