  Baryon-loops vacuum contribution in renormalized models like the Linear sigma
model and the Walecka model give rise to large unnatural interaction
coefficients, indicating that the quantum vacuum is not adequately described by
long-range degrees of freedom. We extend such models into nonrenormalizable
class by introducing an ultraviolet cutoff into the model definition and treat
the Dirac-sea explicitly. In this way, one can avoid unnaturalness. We
calculate the equation of state for symmetric nuclear matter at zero
temperature in a modified $\sigma-\omega$ model. We show that the strong
attraction originating from the Dirac-sea softens the nuclear matter equation
of state and generates a vacuum with dynamically broken symmetry. In this model
the vector-meson is important for the description of normal nuclear matter, but
it obstructs the chiral phase transition. We investigate the chiral phase
transition in this model by incorporating deconfinement at high density. A
first-order quark deconfinement is simulated by changing the active degrees of
freedom from nucleons to quarks at high density. We show that the chiral phase
transition is first-order when quark decouples from the vector-meson and
coincides with the deconfinement critical density.
