Generating the mass gap of the sine-Gordon model
  We discuss in this study the possibility of finding a finite mass gap in the broken phase of the sine-Gordon model in $d=2$ using the functional flows. We demonstrate that the signal of the presence of massive excitations, a finite positively-curved {\em blocked} potential around its minima, is recovered only in our treatment. The usual results based on the flow of the Fourier expansion of the {\em blocked} action are then shown to actually fit a singularity. 
V. Pangon
hep-th cond-mat.stat-mech cond-mat.str-el