We formulate the three dimensional Thirring model on a spacetime lattice and
study it for various even numbers of fermion flavors 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 ultra-violet 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_fc<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.Comment: 50 pages LaTeX, including 16 tables and 20 figures - uses style file
ldd_art.sty (included
