Stiffening of matter in quark-hadron continuity

Abstract

We discuss stiffening of matter in quark-hadron continuity. We introduce a model that relates quark wavefunctions in a baryon and the occupation probability of states for baryons and quarks in dense matter. In dilute regime, the confined quarks contribute to the energy density through the masses of baryons, but do not directly contribute to the pressure, hence the equations of state are very soft. This dilute regime continues until the low momentum states for quarks get saturated; this may happen even before baryons fully overlap, possibly at density slightly above the nuclear saturation density. After the saturation the pressure grows rapidly while changes in energy density are modest, producing a peak in the speed of sound. If we use baryonic descriptions for quark distributions near the Fermi surface, we reach a description similar to the quarkyonic matter model of McLerran and Reddy. With a simple adjustment of quark interactions to get the nucleon mass, our model becomes consistent with the constraints from 1.4-solar mass neutron stars, but the high density part is too soft to account for two-solar mass neutron stars. We delineate the relation between the saturation effects and short range interactions of quarks, suggesting interactions that leave low density equations of state unchanged but stiffen the high density part.

Cooling of Isolated Neutron Stars with Pion Condensation: Possible Fast Cooling in a Low-Symmetry-Energy Model

“…In particular, if exotic states are included, the EOS tends to significantly become soft, and may fail to reproduce 2M stars (hyperon puzzle, but see also Ref. 48 ). Hence, hyperon puzzle is the most crucial condition for the test of exotic-matter EOSs.…”

Peaks of sound velocity in two color dense QCD: quark saturation effects and semishort range correlations

“…We consider the occupation probability, f q = f q c s , of a quark state for a given set of color (c), flavor (q), spin (s) in baryonic matter. We postulate the form [85]…”

“…which in turn constrains the form of B [85]. For the normalization of Q Iq in , we set the spatial probability after momentum integration to be 1.…”

“…Inspired by the work of McLerran and Reddy, one of the authors (T.K.) in this paper introduced a microscopic model of quark-hadron continuity [85]. Although schematic, the model manifestly keeps track the evolution of the occupation probability for quark states.…”

“…In this description, the peak of sound velocity is triggered by the quark saturation effect, while nuclear interactions tend to smooth out the peak structure. The description contains the above-mentioned quarkyonic matter model as a special case [85].…”