529 research outputs found
Statistical Entropy of Schwarzschild Black Holes
The entropy of a seven dimensional Schwarzschild black hole of arbitrary
large radius is obtained by a mapping onto a near extremal self-dual
three-brane whose partition function can be evaluated. The three-brane arises
from duality after submitting a neutral blackbrane, from which the
Schwarzschild black hole can be obtained by compactification, to an infinite
boost in non compact eleven dimensional space-time and then to a Kaluza-Klein
compactification. This limit can be defined in precise terms and yields the
Bekenstein-Hawking value up to a factor of order one which can be set to be
exactly one with the extra assumption of keeping only transverse brane
excitations. The method can be generalized to five and four dimensional black
holes.Comment: 11 pages, LaTex, no figures, corrected typ
On the Nature of the Hagedorn Transition in NCOS Systems
We extend the study of the nature of the Hagedorn transition in NCOS systems
in various dimensions. The canonical analysis results in a microscopic
ionization picture of a bound state system in which the Hagedorn transition is
postponed till irrelevancy. A microcanonical analysis leads to a limiting
Hagedorn behaviour dominated by highly excited, long open strings. The study of
the full phase diagram of the NCOS system using the AdS/CFT correspondence
suggests that the microscopic ionization picture is the correct one. We discuss
some refinements of the ionization mechanism for NCOS systems, including
the formation of a temperature-dependent barrier for the process. Some possible
consequences of this behaviour, including a potential puzzle for , are
discussed. Phase diagrams of a regularized form of NCOS systems are introduced
and do accomodate a phase of long open strings which disappears in the strict
NCOS limit.Comment: 37 pages, 3 Postscript figure
Long time scales and eternal black holes
We discuss the various scales determining the temporal behaviour of
correlation functions in the presence of eternal black holes. We point out the
origins of the failure of the semiclassical gravity approximation to respect a
unitarity-based bound suggested by Maldacena. We find that the presence of a
subleading (in the large-N approximation involved) master field does restore
the compliance with one bound but additional configurations are needed to
explain the more detailed expected time dependence of the Poincare recurrences
and their magnitude.Comment: 10 pages, 6 figures. Presented at Johns Hopkins 2003 and Ahrenshoop
2003 workshop
Remarks on Black Hole Instabilities and Closed String Tachyons
Physical arguments stemming from the theory of black-hole thermodynamics are
used to put constraints on the dynamics of closed-string tachyon condensation
in Scherk--Schwarz compactifications. A geometrical interpretation of the
tachyon condensation involves an effective capping of a noncontractible cycle,
thus removing the very topology that supports the tachyons. A semiclassical
regime is identified in which the matching between the tachyon condensation and
the black-hole instability flow is possible. We formulate a generalized
correspondence principle and illustrate it in several different circumstances:
an Euclidean interpretation of the transition from strings to black holes
across the Hagedorn temperature and instabilities in the brane-antibrane
system.Comment: harvmac, 20 pp, 4 eps figures. Contribution to Jacob Bekenstein's
Festschrif
Touring the Hagedorn Ridge
We review aspects of the Hagedorn regime in critical string theories, from
basic facts about the ideal gas approximation to the proposal of a global
picture inspired by general ideas of holography. It was suggested that the
condensation of thermal winding modes triggers a first-order phase transition.
We propose, by an Euclidean analogue of the string/black hole correspondence
principle, that the transition is actually related to a topology change in
spacetime. Similar phase transitions induced by unstable winding modes can be
studied in toy models. There, using T-duality of supersymmetric cycles, one can
identify a topology change of the Gregory--Laflamme type, which we associate
with large-N phase transitions of Yang--Mills theories on tori. This essay is
dedicated to the memory of Ian Kogan.Comment: 29 pages, 18 figures, contribution to I.I. Kogan memorial volume,
references adde
On the short-distance structure of irrational non-commutative gauge theories
As shown by Hashimoto and Itzhaki in hep-th/9911057, the perturbative degrees
of freedom of a non-commutative Yang-Mills theory (NCYM) on a torus are
quasi-local only in a finite energy range. Outside that range one may resort to
a Morita equivalent (or T-dual) description appropriate for that energy. In
this note, we study NCYM on a non-commutative torus with an irrational
deformation parameter . In that case, an infinite tower of dual
descriptions is generically needed in order to describe the UV regime. We
construct a hierarchy of dual descriptions in terms of the continued fraction
approximations of . We encounter different descriptions depending on
the level of the irrationality of and the amount of non-locality
tolerated. The behavior turns out to be isomorphic to that found for the phase
structure of the four-dimensional Villain lattice gauge theories, which
we revisit as a warm-up. At large 't Hooft coupling, using the AdS/CFT
correspondance, we find that there are domains of the radial coordinate
where no T-dual description makes the derivative expansion converge. The radial
direction obtains multifractal characteristics near the boundary of AdS.Comment: 17 pages, 4 figures, uses JHEP.cl
Comments on Critical Electric and Magnetic Fields from Holography
We discuss some aspects of critical electric and magnetic fields in a field
theory with holographic dual description. We extend the analysis of
arxiv:1109.2920, which finds a critical electric field at which the Schwinger
pair production barrier drops to zero, to the case of magnetic fields. We first
find that, unlike ordinary weakly coupled theories, the magnetic field is not
subject to any perturbative instability originating from the presence of a
tachyonic ground state in the W-boson spectrum. This follows from the large
value of the 't Hooft coupling \lambda, which prevents the Zeeman interaction
term to overcome the particle mass at high B. Consequently, we study the next
possible B-field instability, i.e. monopole pair production, which is the
S-dual version of the Schwinger effect. Also in this case a critical magnetic
field is expected when the tunneling barrier drops to zero. These
Schwinger-type criticalities are the holographic duals, in the bulk, to the
fields E or B reaching the tension of F1 or D1 strings respectively. We then
discuss how this effect is modified when electric and magnetic fields are
present simultaneously and dyonic states in the spectrum can be pair produced
by a generic E - B background. Finally, we analyze finite temperature effects
on Schwinger criticalities, i.e. in the AdS-Schwarzshild black hole background.Comment: 33 pages, 4 figures; v2: refs added; v3: typos corrected, to appear
on JHE
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