41 research outputs found
Early Time Dynamics in Heavy Ion Collisions from AdS/CFT Correspondence
We study the matter produced in heavy ion collisions assuming that this
matter is strongly interacting and employing AdS/CFT correspondence to
investigate its dynamics. At late proper times we show that Bjorken
hydrodynamics solution, obtained recently by Janik and Peschanski using
gauge-gravity duality [hep-th/0512162], can be singled out by simply requiring
that the metric tensor is a real and single-valued function of the coordinates
everywhere in the bulk, without imposing any constraints on the curvature
invariant. At early proper times we use similar strategy to show that the
energy density approaches a constant as proper time goes to zero. We therefore
demonstrate that the strong coupling dynamics incorporates the isotropization
transition in heavy ion collisions. By matching our early-time regime with the
late-time one of Janik and Peschanski we estimate the isotropization time at
RHIC to be approximately 0.3 fm/c, in good agreement with results of
hydrodynamic simulations.Comment: 24 pages, 2 figures; v2: some references added, minor typos correcte
Heavy Quark Potential at Finite Temperature Using the Holographic Correspondence
We revisit the calculation of a heavy quark potential in N =4 supersymmetric
Yang-Mills theory at finite temperature using the AdS/CFT correspondence. As is
widely known, the potential calculated in the pioneering works of Rey et al.
and Brandhuber et al. is zero for separation distances r between the quark and
the anti-quark above a certain critical separation, at which the potential has
a kink. We point out that by analytically continuing the string configurations
into the complex plane, and using a slightly different renormalization
subtraction, one obtains a smooth non-zero (negative definite) potential
without a kink. The obtained potential also has a non-zero imaginary
(absorptive) part for separations r > r_c = 0.870/\pi T . At large separations
r the real part of the potential does not exhibit the exponential Debye falloff
expected from perturbation theory and instead falls off as a power law,
proportional to 1/r^4 for r > r_0 = 2.702 / \pi T.Comment: 5 pages, 3 figures. Title modified. Discussion extended and
references modifie
Desalination using renewable energy sources on the arid islands of South Aegean Sea
Water and energy supply are strongly interrelated and their efficient management is crucial for a sustainable future. Water and energy systems on several Greek islands face a number of pressing issues. Water supply is problematic as regards both to the water quality and quantity. There is significant lack of water on several islands and this is mainly dealt with tanker vessels which transport vast amounts of water from the mainland. At the same time island energy systems are congested and rely predominanty on fossil fuels, despite the abundant renewable energy potential. These issues may be addressed by combining desalination and renewable energy technologies. It is essential to analyse the feasibility of this possibility. This study focuses on developing a tool capable of designing and optimally sizing desalination and renewable energy units. Several parameters regarding an island's water demandand the desalination's energy requirements are taken into account as well as input data which concern technological performance, resource availability and economic data. The tool is applied on three islands in the South Aegean Sea, Patmos (large), Lipsoi (medium) ad Thirasia (small). Results of the modelling exercise show that the water selling price ranges from 1.45 euro/m^3 for the large island, while the corresponding value is about 2.6 euro/m^3 for the small island, figures significantly lower than the current water cost (7-9 euro/m^3)
Allogeneic Mesenchymal Stromal Cell Injection to Alleviate Ischemic Heart Failure Following Arterial Switch Operation.
Cell therapy is a promising tool to prevent and treat heart failure in congenital heart disease. We report the first case of intramyocardial injection of allogeneic mesenchymal stromal cells as rescue therapy in a neonate with ischemic heart failure following arterial switch procedure for isolated transposition of the great arteries. (Level of Difficulty: Advanced.
Asymmetric Collision of Two Shock Waves in AdS_5
We consider high energy collisions of two shock waves in AdS_5 as a model of
ultrarelativistic nucleus-nucleus collisions in the boundary theory. We first
calculate the graviton field produced in the collisions in the NLO and NNLO
approximations, corresponding to three- and four-graviton exchanges with the
shock waves. We then consider the asymmetric limit where the energy density in
one shock wave is much higher than in the other one. In the boundary theory
this setup corresponds to proton-nucleus collisions, with the nucleus being the
denser of the two shock waves and the proton being the less dense one.
Employing the eikonal approximation we find the exact high energy analytic
solution for the metric in AdS_5 for the asymmetric collision of two
delta-function shock waves. The solution resums all-order graviton exchanges
with the "nucleus" shock wave and a single-graviton exchange with the "proton"
shock wave. Using the holographic renormalization prescription we read off the
energy-momentum tensor of the matter produced in proton-nucleus collisions. We
show in explicit detail that in the boundary theory the proton is completely
stopped by strong-coupling interactions with the nucleus, in agreement with our
earlier results. We also apply the eikonal technique to the asymmetric
collision of two unphysical delta-prime shock waves, which we introduced in an
earlier work as a means of modeling nuclear collisions with weak coupling
initial dynamics. We obtain a surprising result that, for delta-prime shock
waves, the multiple bulk graviton exchange series giving the leading
energy-dependent contribution to the energy-momentum tensor terminates at the
order of two graviton exchanges with the nucleus.Comment: 44 pages, 8 figures; v2: typos corrected, references added; v3: a
subsection added, more typos correcte
Gravitational collapse and thermalization in the hard wall model
We study a simple example of holographic thermalization in a confining field
theory: the homogeneous injection of energy in the hard wall model. Working in
an amplitude expansion, we find black brane formation for sufficiently fast
energy injection and a scattering wave solution for sufficiently slow
injection. We comment on our expectations for more sophisticated holographic
QCD models.Comment: 33 pages, 5 figure
Holographic phase diagram of quark-gluon plasma formed in heavy-ions collisions
The phase diagram of quark gluon plasma (QGP) formed at a very early stage
just after the heavy ion collision is obtained by using a holographic dual
model for the heavy ion collision. In this dual model colliding ions are
described by the charged shock gravitational waves. Points on the phase diagram
correspond to the QGP or hadronic matter with given temperatures and chemical
potentials. The phase of QGP in dual terms is related to the case when the
collision of shock waves leads to formation of trapped surface. Hadronic matter
and other confined states correspond to the absence of trapped surface after
collision.
Multiplicity of the ion collision process is estimated in the dual language
as area of the trapped surface. We show that a non-zero chemical potential
reduces the multiplicity. To plot the phase diagram we use two different dual
models of colliding ions, the point and the wall shock waves, and find
qualitative agreement of the results.Comment: 33 pages, 14 figures, typos correcte
The dynamics of quark-gluon plasma and AdS/CFT
In these pedagogical lectures, we present the techniques of the AdS/CFT
correspondence which can be applied to the study of real time dynamics of a
strongly coupled plasma system. These methods are based on solving
gravitational Einstein's equations on the string/gravity side of the AdS/CFT
correspondence. We illustrate these techniques with applications to the
boost-invariant expansion of a plasma system. We emphasize the common
underlying AdS/CFT description both in the large proper time regime where
hydrodynamic dynamics dominates, and in the small proper time regime where the
dynamics is far from equilibrium. These AdS/CFT methods provide a fascinating
arena interrelating General Relativity phenomenae with strongly coupled gauge
theory physics.Comment: 35 pages, 3 figures. Lectures at the 5th Aegean summer school, `From
gravity to thermal gauge theories: the AdS/CFT correspondence'. To appear in
the proceedings in `Lecture Notes in Physics
Long-Range Rapidity Correlations in Heavy Ion Collisions at Strong Coupling from AdS/CFT
We use AdS/CFT correspondence to study two-particle correlations in heavy ion
collisions at strong coupling. Modeling the colliding heavy ions by shock waves
on the gravity side, we observe that at early times after the collision there
are long-range rapidity correlations present in the two-point functions for the
glueball and the energy-momentum tensor operators. We estimate rapidity
correlations at later times by assuming that the evolution of the system is
governed by ideal Bjorken hydrodynamics, and find that glueball correlations in
this state are suppressed at large rapidity intervals, suggesting that
late-time medium dynamics can not "wash out" the long-range rapidity
correlations that were formed at early times. These results may provide an
insight on the nature of the "ridge" correlations observed in heavy ion
collision experiments at RHIC and LHC, and in proton-proton collisions at LHC.Comment: 32 pages, 2 figures; v2: typos corrected, references adde
A holographic model for the fractional quantum Hall effect
Experimental data for fractional quantum Hall systems can to a large extent
be explained by assuming the existence of a modular symmetry group commuting
with the renormalization group flow and hence mapping different phases of
two-dimensional electron gases into each other. Based on this insight, we
construct a phenomenological holographic model which captures many features of
the fractional quantum Hall effect. Using an SL(2,Z)-invariant
Einstein-Maxwell-axio-dilaton theory capturing the important modular
transformation properties of quantum Hall physics, we find dyonic diatonic
black hole solutions which are gapped and have a Hall conductivity equal to the
filling fraction, as expected for quantum Hall states. We also provide several
technical results on the general behavior of the gauge field fluctuations
around these dyonic dilatonic black hole solutions: We specify a sufficient
criterion for IR normalizability of the fluctuations, demonstrate the
preservation of the gap under the SL(2,Z) action, and prove that the
singularity of the fluctuation problem in the presence of a magnetic field is
an accessory singularity. We finish with a preliminary investigation of the
possible IR scaling solutions of our model and some speculations on how they
could be important for the observed universality of quantum Hall transitions.Comment: 86 pages, 16 figures; v.2 references added, typos fixed, improved
discussion of ref. [39]; v.3 more references added and typos fixed, several
statements clarified, v.4 version accepted for publication in JHE