  We investigate the two-dimensional Hubbard model with next-nearest-neighbor
hopping, t', using the dynamical cluster approximation. We confirm the
existence of a first-order phase-separation transition terminating at a
second-order critical point at filling n_c(t') and temperature T_ps(t'). We
find that as t' approaches zero, T_ps(t') vanishes and n_c(t') approaches the
filling associated with the quantum critical point separating the Fermi liquid
from the pseudogap phase. We propose that the quantum critical point under the
superconducting dome is the zero-temperature limit of the line of second-order
critical points.
