Thermodynamics of strange quark matter with the density-dependent bag constant

Abstract

The thermodynamics of strange quark matter with density dependent bag constant are studied selfconsistently in the framework of the general ensemble theory and the MIT bag model. In our treatment, an additional term is found in the expression of pressure. With the additional term, the zero pressure locates exactly at the lowest energy state, indicating that our treatment is a self-consistently thermodynamic treatment. The self-consistent equations of state of strange quark matter in both the normal and color-flavor-locked phase are derived. They are both softer than the inconsistent ones. Strange stars in both the normal and color-flavor locked phase have smaller masses and radii in our treatment. It is also interesting to find that the energy density at a star surface in our treatment is much higher than that in the inconsistent treatment for both phases. Consequently, the surface properties and the corresponding observational properties of strange stars in our treatment are different from those in the inconsistent treatment.dense matter, bag model, quark stars, thermodynamic functions and equations of stateThe conjecture that strange quark matter (SQM) may be the true ground state of the quantum chromodynamics (QCD) vacuum was proposed nearly three decades ago [1−4] . The possible existence of strange stars has attracted many authors [5,6] , since it is an alternative way to find free quarks other than terrestrial high energy heavy-ion collision experiments. Usually phenomenological models, such as the MIT bag model, are adopted in the study of hadrons and SQM because of the difficulty of QCD in non-perturbative domain. It is the purpose of this paper to study the thermodynamics of SQM with the density-dependent bag constant self-consistently.In the MIT bag model, hadrons are taken as bubbles emerging from the QCD vacuum. Quarks bound in those bubbles have a weak interaction among them, which is known as asymptotic freedom. To form such bubbles in the QCD vacuum, additional energy E B = BV is required. The bag constant B is understood as the background energy density in those bubbles and the net inward pressure exerted on them by the surrounding vacuum.Along with the increase of energy density, deconfinement phase transition (hadron-quark phase transition) is believed to happen. When such phase

Recent progress in theoretical nuclear physics related to large-scale scientific facilities

“…The thermodynamics of strange quark matter with density dependent bag constant is studied self-consistently in the framework of the general ensemble theory and the MIT bag model [28]. In this work, an additional term is found in the expression of pressure.…”