Thermodynamics of the two--dimensional O(3) non linear sigma model with   Fixed-Point lattice action
  We calculate the free energy density of the two dimensional O(3) non linear sigma model over a large temperature region. At high temperatures the calculations could be done by perturbation theory whereas in the low temperature regime we used Monte-Carlo simulations. Using the Fixed--Point action the results do not show any remarkable cut-off effects and furthermore the behaviour of these effects is nearly the same over the whole temperature region. The results of the Fixed-Point action are then compared to those of the standard Wilson action. 
S.P. Spiegel (Institut fuer Theoretische Physik, Zuerich, Switzerland)