154 research outputs found
Entropy of Thermally Excited Black Rings
A string theory description of near extremal black rings is proposed. The
entropy is computed and the thermodynamic properties are derived for a large
family of black rings that have not yet been constructed in supergravity. It is
also argued that the most general black ring in N=8 supergravity has 21
parameters up to duality.Comment: 17 pages; v2: minor edits and refs adde
Closed-String Tachyons and the Hagedorn Transition in AdS Space
We discuss some aspects of the behaviour of a string gas at the Hagedorn
temperature from a Euclidean point of view. Using AdS space as an infrared
regulator, the Hagedorn tachyon can be effectively quasi-localized and its
dynamics controled by a finite energetic balance. We propose that the off-shell
RG flow matches to an Euclidean AdS black hole geometry in a generalization of
the string/black-hole correspondence principle. The final stage of the RG flow
can be interpreted semiclassically as the growth of a cool black hole in a
hotter radiation bath. The end-point of the condensation is the large Euclidean
AdS black hole, and the part of spacetime behind the horizon has been removed.
In the flat-space limit, holography is manifest by the system creating its own
transverse screen at infinity. This leads to an argument, based on the
energetics of the system, explaining why the non-supersymmetric type 0A string
theory decays into the supersymmetric type IIB vacuum. We also suggest a notion
of `boundary entropy', the value of which decreases along the line of flow.Comment: 24 pages, Harvmac. 2 Figures. Typos corrected and reference adde
Solitonic Strings and BPS Saturated Dyonic Black Holes
We consider a six-dimensional solitonic string solution described by a
conformal chiral null model with non-trivial superconformal transverse
part. It can be interpreted as a five-dimensional dyonic solitonic string wound
around a compact fifth dimension. The conformal model is regular with the
short-distance (`throat') region equivalent to a WZW theory. At distances
larger than the compactification scale the solitonic string reduces to a dyonic
static spherically-symmetric black hole of toroidally compactified heterotic
string. The new four-dimensional solution is parameterised by five charges,
saturates the Bogomol'nyi bound and has nontrivial dilaton-axion field and
moduli fields of two-torus. When acted by combined T- and S-duality
transformations it serves as a generating solution for all the static
spherically-symmetric BPS-saturated configurations of the low-energy heterotic
string theory compactified on six-torus. Solutions with regular horizons have
the global space-time structure of extreme Reissner-Nordstrom black holes with
the non-zero thermodynamic entropy which depends only on conserved (quantised)
charge vectors. The independence of the thermodynamic entropy on moduli and
axion-dilaton couplings strongly suggests that it should have a microscopic
interpretation as counting degeneracy of underlying string configurations. This
interpretation is supported by arguments based on the corresponding
six-dimensional conformal field theory. The expression for the level of the WZW
theory describing the throat region implies a renormalisation of the string
tension by a product of magnetic charges, thus relating the entropy and the
number of oscillations of the solitonic string in compact directions.Comment: 27 Pages, uses RevTeX (solution for the axion field corrected,
erratum to appear in Phys. Rev. D
On fluctuations of closed string tachyon solitons
We discuss fluctuations on solitons in the dilaton/graviton/tachyon system
using the low energy effective field theory approach. It is shown that closed
string solitons are free of tachyons in this approximation, regardless of the
exact shape of the tachyon potential.Comment: 13 pages, 1 figure, uses JHEP3.cl
Closed String Tachyon Condensation on Twisted Circles
We study IIA/B string theory compactified on twisted circles. These models
possess closed string tachyons and reduce to type 0B/A theory in a special
limit. Using methods of gauged linear sigma models and mirror symmetry we
construct a conformal field theory which interpolates between these models and
flat space via an auxiliary Liouville direction. Interpreting motion in the
Liouville direction as renormalization group flow, we argue that the end point
of tachyon condensation in all these models (including 0B/A theory) is
supersymmetric type II theory. We also find a zero-slope limit of these models
which is best described in a T-dual picture as a type II NS-NS fluxbrane. In
this limit tachyon condensation is an interesting and well posed problem in
supergravity. We explicitly determine the tachyon as a fluctuation of
supergravity fields, and perform a rudimentary numerical analysis of the
relevant flows.Comment: 21 pages plus appendices (12 pages), harvmac, 1 fig, v2: minor
changes and references added, v3: minor changes version published in JHE
Computing in String Field Theory Using the Moyal Star Product
Using the Moyal star product, we define open bosonic string field theory
carefully, with a cutoff, for any number of string oscillators and any
oscillator frequencies. Through detailed computations, such as Neumann
coefficients for all string vertices, we show that the Moyal star product is
all that is needed to give a precise definition of string field theory. The
formulation of the theory as well as the computation techniques are
considerably simpler in the Moyal formulation. After identifying a monoid
algebra as a fundamental mathematical structure in string field theory, we use
it as a tool to compute with ease the field configurations for wedge, sliver,
and generalized projectors, as well as all the string interaction vertices for
perturbative as well as monoid-type nonperturbative states. Finally, in the
context of VSFT we analyze the small fluctuations around any D-brane vacuum. We
show quite generally that to obtain nontrivial mass and coupling, as well as a
closed strings, there must be an associativity anomaly. We identify the
detailed source of the anomaly, but leave its study for future work.Comment: 77 pages, LaTeX. v3: corrections of signs or factors (for a list of
corrections see beginning of source file
Random walks and the Hagedorn transition
We study details of the approach to the Hagedorn temperature in string theory
in various static spacetime backgrounds. We show that the partition function
for a {\it single} string at finite temperature is the torus amplitude
restricted to unit winding around Euclidean time. We use the worldsheet path
integral to derive the statement that the the sum over random walks of the
thermal scalar near the Hagedorn transition is precisely the image under a
modular transformation of the sum over spatial configurations of a single
highly excited string. We compute the radius of gyration of thermally excited
strings in . We show that the winding mode indicates an
instability despite the AdS curvature at large radius, and that the negative
mass squared decreases with decreasing AdS radius, much like the type 0
tachyon. We add further arguments to statements by Barbon and Rabinovici, and
by Adams {\it et. al.}, that the Euclidean AdS black hole can thought of as a
condensate of the thermal scalar. We use this to provide circumstantial
evidence that the condensation of the thermal scalar decouples closed string
modes.Comment: 34 pages (7 of references), 5 figures. v2: Reference added, grant
acknowledgement added, typos correcte
Classical and Thermodynamic Stability of Black Branes
It is argued that many non-extremal black branes exhibit a classical
Gregory-Laflamme instability if, and only if, they are locally
thermodynamically unstable. For some black branes, the Gregory-Laflamme
instability must therefore disappear near extremality. For the black -branes
of the type II supergravity theories, the Gregory-Laflamme instability
disappears near extremality for but persists all the way down to
extremality for (the black D3-brane is not covered by the analysis of
this paper). This implies that the instability also vanishes for the
near-extremal black M2 and M5-brane solutions.Comment: 21 pages, LaTeX. v2: Various points clarified, typos corrected and
reference adde
Closed string tachyons, flips and conifolds
Following the analysis of tachyons and orbifold flips described in
hep-th/0412337, we study nonsupersymmetric analogs of the supersymmetric
conifold singularity and show using their toric geometry description that they
are nonsupersymmetric orbifolds of the latter. Using linear sigma models, we
see that these are unstable to localized closed string tachyon condensation and
exhibit flip transitions between their two small resolutions (involving
2-cycles), in the process mediating mild dynamical topology change. Our
analysis shows that the structure of these nonsupersymmetric conifolds as
quotients of the supersymmetric conifold obstructs the 3-cycle deformation of
such singularities, suggesting that these nonsupersymmetric conifolds decay by
evolving towards their stable small resolutions.Comment: Latex, 22 pgs, 2 figs. v4: matches JHEP version, 29 pgs, 3 figures,
more elaborate Introduction, various clarifications adde
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