7 research outputs found
Comments on holographic star and the dual QGP
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 . The QGP with negative heat capacity
produced at higher temperature will still condensate completely into a gas of
confined hadron.Comment: 30 pages, 9 figures, to be published in JHE
Extended DBI massive gravity with generalized fiducial metric
We consider an extended model of DBI massive gravity by generalizing the
fiducial metric to be an induced metric on the brane corresponding to a domain
wall moving in five-dimensional Schwarzschild-Anti-de Sitter spacetime. The
model admits all solutions of FLRW metric including flat, closed and open
geometries while the original one does not. The background solutions can be
divided into two branches namely self-accelerating branch and normal branch.
For the self-accelerating branch, the graviton mass plays the role of
cosmological constant to drive the late-time acceleration of the universe. It
is found that the number degrees of freedom of gravitational sector is not
correct similar to the original DBI massive gravity. There are only two
propagating degrees of freedom from tensor modes. For normal branch, we
restrict our attention to a particular class of the solutions which provides an
accelerated expansion of the universe. It is found that the number of degrees
of freedom in the model is correct. However, at least one of them is ghost
degree of freedom which always present at small scale implying that the theory
is not stable.Comment: 13 pages, 4 figures. Minor changes. A published versio
Magnetized Domain Walls in the Deconfined Sakai-Sugimoto Model at Finite Baryon Density
The magnetized pure pion gradient () phase in the deconfined
Sakai-Sugimoto 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 shows that the excitations behave like a scalar
solitonic free particles. By comparing the free energy of the pion gradient
phase to the competing multiquark-pion gradient (MQ-) phase,
it becomes apparent that the pure pion gradient is less thermodynamically
preferred than the MQ- 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.Comment: 20 pages, 9 figure
Holographic Magnetic Star
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.Comment: 39 pages, 14 figures, 1 table, comments and references added, to
appear in JHE