  The finite-temperature phase diagram of the Hubbard model in $d=3$ is
obtained from renormalization-group analysis. It exhibits, around half filling,
an antiferromagnetic phase and, between 30%--40% electron or hole doping from
half filling, a new $\tau $ phase in which the electron hopping strength $t$
asymptotically becomes infinite under repeated rescalings. Next to the $\tau $
phase, a first-order phase boundary with very narrow phase separation (less
than 2% jump in electron density) occurs. At temperatures above the $\tau $
phase, an incommensurate spin modulation phase is indicated. In $d=2$, we find
that the Hubbard model has no phase transition at finite temperature.
