173 research outputs found
Acoustic black holes for relativistic fluids
We derive a new acoustic black hole metric from the Abelian Higgs model. In
the non-relativistic limit, while the Abelian Higgs model becomes the
Ginzburg-Landau model, the metric reduces to an ordinary Unruh type. We
investigate the possibility of using (type I and II) superconductors as the
acoustic black holes. We propose to realize experimental acoustic black holes
by using spiral vortices solutions from the Navier-stokes equation in the
non-relativistic classical fluids.Comment: 16 pages. typos corrected, contents expande
Early-Time Energy Loss in a Strongly-Coupled SYM Plasma
We carry out an analytic study of the early-time motion of a quark in a
strongly-coupled maximally-supersymmetric Yang-Mills plasma, using the AdS/CFT
correspondence. Our approach extracts the first thermal effects as a small
perturbation of the known quark dynamics in vacuum, using a double expansion
that is valid for early times and for (moderately) ultrarelativistic quark
velocities. The quark is found to lose energy at a rate that differs
significantly from the previously derived stationary/late-time result: it
scales like T^4 instead of T^2, and is associated with a friction coefficient
that is not independent of the quark momentum. Under conditions representative
of the quark-gluon plasma as obtained at RHIC, the early energy loss rate is a
few times smaller than its late-time counterpart. Our analysis additionally
leads to thermally-corrected expressions for the intrinsic energy and momentum
of the quark, in which the previously discovered limiting velocity of the quark
is found to appear naturally.Comment: 39 pages, no figures. v2: Minor corrections and clarifications.
References added. Version to be published in JHE
Analytical study on holographic superconductors in external magnetic field
We investigate the holographic superconductors immersed in an external
magnetic field by using the analytical approach. We obtain the spatially
dependent condensate solutions in the presence of the magnetism and find
analytically that the upper critical magnetic field satisfies the relation
given in the Ginzburg-Landau theory. We observe analytically the reminiscent of
the Meissner effect where the magnetic field expels the condensate. Extending
to the D-dimensional Gauss-Bonnet AdS black holes, we examine the influence
given by the Gauss-Bonnet coupling on the condensation. Different from the
positive coupling, we find that the negative Gauss-Bonnet coupling enhances the
condensation when the external magnetism is not strong enough.Comment: revised version, to appear in JHE
Critical Trapped Surfaces Formation in the Collision of Ultrarelativistic Charges in (A)dS
We study the formation of marginally trapped surfaces in the head-on
collision of two ultrarelativistic charges in space-time. The metric of
ultrarelativistic charged particles in is obtained by boosting
Reissner-Nordstr\"om space-time to the speed of light. We show that
formation of trapped surfaces on the past light cone is only possible when
charge is below certain critical - situation similar to the collision of two
ultrarelativistic charges in Minkowski space-time. This critical value depends
on the energy of colliding particles and the value of a cosmological constant.
There is richer structure of critical domains in case. In this case
already for chargeless particles there is a critical value of the cosmological
constant only below which trapped surfaces formation is possible. Appearance of
arbitrary small nonzero charge significantly changes the physical picture.
Critical effect which has been observed in the neutral case does not take place
more. If the value of the charge is not very large solution to the equation on
trapped surface exists for any values of cosmological radius and energy density
of shock waves. Increasing of the charge leads to decrease of the trapped
surface area, and at some critical point the formation of trapped surfaces of
the type mentioned above becomes impossible.Comment: 30 pages, Latex, 7 figures, Refs. added and typos correcte
Drag force in a strongly coupled anisotropic plasma
We calculate the drag force experienced by an infinitely massive quark
propagating at constant velocity through an anisotropic, strongly coupled N=4
plasma by means of its gravity dual. We find that the gluon cloud trailing
behind the quark is generally misaligned with the quark velocity, and that the
latter is also misaligned with the force. The drag coefficient can be
larger or smaller than the corresponding isotropic value depending on the
velocity and the direction of motion. In the ultra-relativistic limit we find
that generically . We discuss the conditions under which this
behaviour may extend to more general situations.Comment: 25 pages, 13 figures; v2: minor changes, added reference
Nuclear matter to strange matter transition in holographic QCD
We construct a simple holographic QCD model to study nuclear matter to
strange matter transition. The interaction of dense medium and hadrons is taken
care of by imposing the force balancing condition for stable D4/D6/D6
configuration. By considering the intermediate and light flavor branes
interacting with baryon vertex homogeneously distributed along R^3 space and
requesting the energy minimization, we find that there is a well defined
transition density as a function of current quark mass. We also find that as
density goes up very high, intermediate (or heavy) and light quarks populate
equally as expected from the Pauli principle. In this sense, the effect of the
Pauli principle is realized as dynamics of D-branes.Comment: 13 pages, 14 figure
Self-bound dense objects in holographic QCD
We study a self-bound dense object in the hard wall model. We consider a
spherically symmetric dense object which is characterized by its radial density
distribution and non-uniform but spherically symmetric chiral condensate. For
this we analytically solve the partial differential equations in the hard wall
model and read off the radial coordinate dependence of the density and chiral
condensate according to the AdS/CFT correspondence. We then attempt to describe
nucleon density profiles of a few nuclei within our framework and observe that
the confinement scale changes from a free nucleon to a nucleus. We briefly
discuss how to include the effect of higher dimensional operator into our
study. We finally comment on possible extensions of our work.Comment: 17 pages, 5 figures, figures replaced, minor revision, to appear in
JHE
Holographic Hadrons in a Confining Finite Density Medium
We study a sector of the hadron spectrum in the presence of finite baryon
density. We use a non-supersymmetric gravity dual to a confining guage theory
which exhibits a running dilaton. The interaction of mesons with the finite
density medium is encoded in the dual theory by a force balancing between
flavor D7-branes and a baryon vertex provided by a wrapped D5-brane. When the
current quark mass m_q is sufficiently large, the meson mass reduces,
exhibiting an interesting spectral flow as we increase the baryon density while
it has a more complicated behaviour for very small m_q.Comment: 34 pages, 20 figures, errors for some figures are fixe
Modulation of Sn concentration in ZnO nanorod array: intensification on the conductivity and humidity sensing properties
Tin (Sn)-doped zinc oxide (ZnO) nanorod arrays (TZO) were synthesized onto aluminum-doped ZnO-coated glass substrate via a facile sonicated solâgel immersion method for humidity sensor applications. These nanorod arrays were grown at different Sn concentrations ranging from 0.6 to 3 at.%. X-ray diffraction patterns showed that the deposited TZO arrays exhibited a wurtzite structure. The stress/strain condition of the ZnO film metamorphosed from tensile strain/compressive stress to compressive strain/tensile stress when the Sn concentrations increased. Results indicated that 1 at.% Sn doping of TZO, which has the lowest tensile stress of 0.14 GPa, generated the highest conductivity of 1.31 S cmâ 1. In addition, 1 at.% Sn doping of TZO possessed superior sensitivity to a humidity of 3.36. These results revealed that the optimum performance of a humidity-sensing device can be obtained mainly by controlling the amount of extrinsic element in a ZnO film
Holographic zero sound at finite temperature in the Sakai-Sugimoto model
In this paper, we study the fate of the holographic zero sound mode at finite
temperature and non-zero baryon density in the deconfined phase of the
Sakai-Sugimoto model of holographic QCD. We establish the existence of such a
mode for a wide range of temperatures and investigate the dispersion relation,
quasi-normal modes, and spectral functions of the collective excitations in
four different regimes, namely, the collisionless quantum, collisionless
thermal, and two distinct hydrodynamic regimes. For sufficiently high
temperatures, the zero sound completely disappears, and the low energy physics
is dominated by an emergent diffusive mode. We compare our findings to
Landau-Fermi liquid theory and to other holographic models.Comment: 1+24 pages, 19 figures, PDFTeX, v2: some comments and references
added, v3: some clarifications relating to the different regimes added,
matches version accepted for publication in JHEP, v4: corrected typo in eq.
(3.18
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