164 research outputs found
Black hole thermodynamics from quantum gravity
The semiclassical approximation is studied on hypersurfaces approaching the
union of future null infinity and the event horizon on a large class of four
dimensional black hole backgrounds. Quantum fluctuations in the background
geometry are shown to lead to a breakdown of the semiclassical approximation in
these models. The boundary of the region where the semiclassical approximation
breaks down is used to define a `stretched horizon'. It is shown that the same
effect that brings about the breakdown in semiclassical evolution associates a
temperature and an entropy to the region behind the stretched horizon, and
identifies the microstates that underlie the thermodynamical properties. The
temperature defined in this way is equal to that of the black hole and the
entropy is equal to the Bekenstein entropy up to a factor of order unity.Comment: Latex, 18 pages, no figure
Properties of D-Branes in Matrix Model of IIB Superstring
We discuss properties of D-brane configurations in the matrix model of type
IIB superstring recently proposed by Ishibashi, Kawai, Kitazawa and Tsuchiya.
We calculate central charges in supersymmetry algebra at infinite N and
associate them with one- and five-branes present in IIB superstring theory. We
consider classical solutions associated with static three- and five-branes and
calculate their interactions at one loop in the matrix model. We discuss some
aspects of the matrix-model formulation of IIB superstring.Comment: 15pp., Latex, v2: a few typos corrected, v3: coefficient in Eq.(3.19)
correcte
Quantum Hall Effect in a Holographic Model
We consider a holographic description of a system of strongly coupled
fermions in 2+1 dimensions based on a D7-brane probe in the background of
D3-branes, and construct stable embeddings by turning on worldvolume fluxes. We
study the system at finite temperature and charge density, and in the presence
of a background magnetic field. We show that Minkowski-like embeddings that
terminate above the horizon describe a family of quantum Hall states with
filling fractions that are parameterized by a single discrete parameter. The
quantization of the Hall conductivity is a direct consequence of the
topological quantization of the fluxes. When the magnetic field is varied
relative to the charge density away from these discrete filling fractions, the
embeddings deform continuously into black-hole-like embeddings that enter the
horizon and that describe metallic states. We also study the thermodynamics of
this system and show that there is a first order phase transition at a critical
temperature from the quantum Hall state to the metallic state.Comment: v2: 27 pages, 12 figures. There is a major revision in the
quantitative analysis. The qualitative results and conclusions are unchanged,
with one exception: we show that the quantum Hall state embeddings, which
exist for discrete values of the filling fraction, deform continuously into
metallic state embeddings away from these filling fraction
p-p' System with B-field, Branes at Angles and Noncommutative Geometry
We study the generic system in the presence of constant NS
2-form field. We derive properties concerning with the
noncommutativity of D-brane worldvolume, the Green functions and the spectrum
of this system. In the zero slope limit, a large number of light states appear
as the lowest excitations in appropriate cases. We are able to relate the
energies of the lowest states after the GSO projection with the configurations
of branes at angles. Through analytic continuation, the system is compared with
the branes with relative motion.Comment: 21 pages, Latex. References regarding to section 3 and 4 added. Typos
correcte
Black Holes with Multiple Charges and the Correspondence Principle
We consider the entropy of near extremal black holes with multiple charges in
the context of the recently proposed correspondence principle of Horowitz and
Polchinski, including black holes with two, three and four Ramond-Ramond
charges. We find that at the matching point the black hole entropy can be
accounted for by massless open strings ending on the D-branes for all cases
except a black hole with four Ramond-Ramond charges, in which case a possible
resolution in terms of brane-antibrane excitations is considered.Comment: 26 pages, harvmac, minor correction
Topologically induced local P and CP violation in QCD x QED
The existence of topological solutions and axial anomaly open a possibility
of P and CP violation in QCD. For a reason that has not yet been established
conclusively, this possibility is not realized in strong interactions - the
experimental data indicate that a global P and CP violation in QCD is absent.
Nevertheless, the fluctuations of topological charge in QCD vacuum, although
not observable directly, are expected to play an important role in the breaking
of symmetry and in the mass spectrum and other properties of hadrons.
Moreover, in the presence of very intense external electromagnetic fields
topological solutions of QCD can induce local P- and CP-odd effects in the
gauge theory that can be observed in experiment
directly. Here I show how these local parity-violating phenomena can be
described by using the Maxwell-Chern-Simons, or axion, electrodynamics as an
effective theory. Local P- and CP- violation in hot QCD matter can be observed
in experiment through the "chiral magnetic effect" - the separation of electric
charge along the axis of magnetic field. Very recently, STAR Collaboration
presented an observation of the electric charge asymmetry with respect to
reaction plane in relativistic heavy ion collisions at RHIC.Comment: 24 pages, 6 figures; prepared for the special issue of Annals of
Physic
Phase transition between the BTZ black hole and AdS space
In three dimensions, a phase transition occurs between the non-rotating BTZ
black hole and the massless BTZ black hole. Further, introducing the mass of a
conical singularity, we show that a transition between the non-rotating BTZ
black hole and thermal AdS space is also possible.Comment: 10 pages, 4 eps figures, version to appear in PL
Entropies of Scalar Fields on Three Dimensional Black Holes
Thermodynamics of scalar fields is investigated in three dimensional black
hole backgrounds in two approaches. One is mode expansion and direct
computation of the partition sum, and the other is the Euclidean path integral
approach. We obtain a number of exact results, for example, mode functions,
Hartle-Hawking Green functions on the black holes, Green functions on a cone
geometry, free energies and entropies. They constitute reliable bases for the
thermodynamics of scalar fields. It is shown that thermodynamic quantities
largely depend upon the approach to calculate them, boundary conditions for the
scalar fields and regularization method. We find that, in general, the
entropies are not proportional to the area of the horizon and that their
divergent parts are not necessarily due to the existence of the horizon.Comment: 35 pages, Latex, 1 figure, postscript file attached at the en
Anomalies and the chiral magnetic effect in the Sakai-Sugimoto model
In the chiral magnetic effect an imbalance in the number of left- and
right-handed quarks gives rise to an electromagnetic current parallel to the
magnetic field produced in noncentral heavy-ion collisions. The chiral
imbalance may be induced by topologically nontrivial gluon configurations via
the QCD axial anomaly, while the resulting electromagnetic current itself is a
consequence of the QED anomaly. In the Sakai-Sugimoto model, which in a certain
limit is dual to large-N_c QCD, we discuss the proper implementation of the QED
axial anomaly, the (ambiguous) definition of chiral currents, and the
calculation of the chiral magnetic effect. We show that this model correctly
contains the so-called consistent anomaly, but requires the introduction of a
(holographic) finite counterterm to yield the correct covariant anomaly.
Introducing net chirality through an axial chemical potential, we find a
nonvanishing vector current only before including this counterterm. This seems
to imply the absence of the chiral magnetic effect in this model. On the other
hand, for a conventional quark chemical potential and large magnetic field,
which is of interest in the physics of compact stars, we obtain a nontrivial
result for the axial current that is in agreement with previous calculations
and known exact results for QCD.Comment: 35 pages, 4 figures, v2: added comments about frequency-dependent
conductivity at the end of section 4; references added; version to appear in
JHE
Black Hole Entropy and Superconformal Field Theories on Brane-Antibrane Systems
We obtain the enropy of Schwarzschild and charged black holes in D>4 from
superconformal gases that live on p=10-D dimensional brane-antibrane systems
wrapped on T^p. The preperties of the strongly coupled superconformal theories
such as the appearance of hidden dimensions (for p=1,4) and fractional strings
(for p=5) are crucial for our results. In all cases, the Schwarzschild radius
is given by the transverse fluctuations of the branes and antibranes due to the
finite temperature. We show that our results can be generalized to multicharged
black holes.Comment: 24 pages in phyzzx.te
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