Three-dimensional thirring model for small N-f

We formulate the three-dimensional Thirring model on a space-time lattice and study it for various even numbers of fermion flavours N-f by Monte Carlo simulation. We find clear evidence for spontaneous chiral symmetry breaking at strong coupling, contradicting the predictions of the 1/N-f expansion. The critical point appears to correspond to an ultraviolet fixed point of the renormalisation group; a fit to a RG-inspired equation of state in the vicinity of the fixed point yields distinct critical exponents for N-f = 2 and N-f = 4, while no fit is found for N-f = 6, suggesting there is a critical number N-f < 6 beyond which no chiral symmetry breaking occurs. The spectrum of the N-f = 2 theory is studied; the states examined vary sharply but continuously across the transition. (C) 1997 Elsevier Science B.V.