We study static AdS star in generic dimension. The dependence of the mass limit to the bulk fermion mass is explored. In the bulk conformal limit, the mass limit saturates at a value identical to the mass limit of a radiation star or the AdS space filling with pure radiation. The temperature and entropy of the degenerate AdS star in the bulk conformal limit is zero in contrast to the radiation star. Holographically, the universal mass limit corresponds to the upper limit of the deconfinement temperature in the dual gauge picture. The QGP at this temperature is dual to the large black hole and the heat capacity is positive. When the fermion mass increases, the mass limit falls into the range of the small black holes. We found that even though the small black hole has negative heat capacity, the AdS box allows possibilities that it remains in thermal equilibrium with the radiation as long as the size of the black hole is not smaller than a critical size. Consequently, the dual QGP with negative heat capacity can be produced and remains stable thermodynamically at temperature below a saturation temperature T 2 . The QGP with negative heat capacity produced at higher temperature will still condensate completely into a gas of confined hadron.

Abstract:The magnetized pure pion gradient (▽ϕ) phase in the deconfined SakaiSugimoto model is explored at zero and finite temperature. We found that the temperature has very small effects on the phase. The thermodynamical properties of the phase show that the excitations behave like scalar solitonic free particles. By comparing the free energy of the pion gradient phase to the competing multiquark-pion gradient (MQ-▽ϕ) phase, it becomes apparent that the pure pion gradient is less thermodynamically preferred than the MQ-▽ϕ phase. However, in the parameter space where the baryonic chemical potential is smaller than the onset value of the multiquark, the dominating magnetized nuclear matter is the pion gradient phase.

A warm fermionic AdS star under a homogeneous magnetic field is explored. We obtain the relativistic Landau levels by using Dirac equation and use the Tolman-Oppenheimer-Volkoff (TOV) equation to study the physical profiles of the star. Bulk properties such as sound speed, adiabatic index, and entropy density within the star are calculated analytically and numerically. Bulk temperature increases the mass limit of the AdS star but external magnetic field has the opposite effect. The results are partially interpreted in terms of the pre-thermalization process of the gauge matter at the AdS boundary after the mass injection. The entropy density is found to demonstrate similar temperature dependence as the magnetic black brane in the AdS in certain limits regardless of the different nature of the bulk and Hawking temperatures. Total entropy of the AdS star is also found to be an increasing function of the bulk temperature and a decreasing function of the magnetic field, similar behaviour to the mass limit. Since both total entropy and mass limit are global quantities, they could provide some hints to the value of entropy and energy of the dual gauge matter before and during the thermalization.

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