Deconfinement, naturalness and the nuclear-quark equation of state

Abstract

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.