Stability of magnetized strange quark matter in the MIT bag model with the density dependent bag pressure

TL;DR

This paper investigates the stability of magnetized strange quark matter within the MIT bag model, considering density-dependent bag pressure, and determines the maximum magnetic field strength sustainable in strange quark stars.

Contribution

It introduces a consistent thermodynamic framework for MSQM with density-dependent bag pressure and identifies the magnetic field limits for stability in strange quark stars.

Findings

Existence of a maximum magnetic field strength (~10^{18} G) for stable MSQM.

The stability window depends on the density dependence parameters of the bag pressure.

The upper bound on the bag pressure vanishes at a specific magnetic field strength.

Abstract

The stability of magnetized strange quark matter (MSQM) is studied in the MIT bag model with the density dependent bag pressure. In the consistent thermodynamic description of MSQM, the quark chemical potentials, the total thermodynamic potential and the anisotropic pressure acquire the corresponding additional term proportional to the density derivative of the bag pressure. The model parameter space is determined, for which MSQM is absolutely stable, i.e., its energy per baryon is less than that of the most stable $^{56}$Fe nucleus under the zero external pressure and vanishing temperature. It is shown that there exists the magnetic field strength $H_{u\,max}$ at which the upper bound $B_\infty^u$ on the asymptotic bag pressure $B_\infty\equiv B(\varrho_B\gg \varrho_0$) ($\varrho_0$ being the nuclear saturation density) from the absolute stability window vanishes. The value of this field, \hbox{$H_{u\,max}\sim$$(1$--$3)\cdot10^{18}$}~G, represents the upper bound on the magnetic field strength, which can be reached in a strongly magnetized strange quark star. It is clarified how the absolute stability window and upper bound on the magnetic field strength are affected by varying the parameters in the Gaussian parametrization for the density dependence of the bag pressure.