The QCD spectrum and phase diagram on the lattice - 1991

Recent numerical computations of the hadron spectrum and phase diagram in lattice QCD are summarized. Incremental improvements in the quality of spectrum calculations give increasing credibility to the claim that lattice calculations reproduce the physical hadron spectrum as the quark mass is lowered. A transition to high temperature behavior is clear, both for Kogut-Susskind and Wilson fermions. For four flavors of Kogut-Susskind fermions the transition appears to be first order. However, for two flavors no indications of metastability are seen. Hints of new phenomena with many flavors of quarks are seen with both Kogut-Susskind and Wilson quarks. Observations of the masses and spatial structure of screening propagators give information about the nature of high temperature QCD. For Wilson fermions it remains difficult to simulate with small pion mass, both for the zero temperature and high temperature simulations.