9,018 research outputs found
Theta Dependence In The Large N Limit Of Four-Dimensional Gauge Theories
The theta dependent of pure gauge theories in four dimensions can be studied
using a duality of large N gauge theories with string theory on a certain
spacetime. Via this duality, one can argue that for every theta, there are
infinitely many vacua that are stable in the large N limit. The true vacuum,
found by minimizing the energy in this family, is a smooth function of theta
except at theta equal to pi, where it jumps. This jump is associated with
spontaneous breaking of CP symmetry. Domain walls separating adjacent vacua are
described in terms of wrapped sixbranes.Comment: 8 p
Existence of Majorana fermions for M-branes wrapped in space and time
We show that it is possible to define Majorana (s)pinor fields on M-branes
which have been identified under the action of the antipodal map on the adS
factor of the throat geometry, or which have been wrapped on two-cycles of
arbitrary genus. This is an important consistency check, since it means that
one may still take the generators of supertranslations in superspace to
transform as Majorana fermions under the adjoint action of , even
though the antipodally identified M2-brane is {\it not} space-orientable. We
point out that similar conclusions hold for any p-branes which have the generic
(adS)(Sphere) throat geometry.Comment: 10 pages REVTe
New Compactifications of Supergravities and Large N QCD
We construct supergravity backgrounds representing non-homogeneous
compactifications of d=10,11 supergravities to four dimensions, which cannot be
written as a direct product. The geometries are regular and approach
or at infinity; they are generically
non-supersymmetric, except in a certain "extremal" limit, where a Bogomol'nyi
bound is saturated and a naked singularity appears. By using these spaces, one
can construct a model of QCD that generalizes by one (or two) extra parameters
a recently proposed model of QCD based on the non-extremal D4 brane. This
allows for some extra freedom to circumvent some (but not all) limitations of
the simplest version.Comment: two small misprints corrected, to appear in Nucl.Phys.B, 17 pages,
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Some Comments on Branes, G-flux, and K-theory
This is a summary of a talk at Strings2000 explaining three ways in which
string theory and M-theory are related to the mathematics of K-theory.Comment: 10pp., late
Chern-Simons Field Theory and Completely Integrable Systems
We show that the classical non-abelian pure Chern-Simons action is related in
a natural way to completely integrable systems of the Davey-Stewartson
hyerarchy, via reductions of the gauge connection in Hermitian spaces and by
performing certain gauge choices. The B\"acklund Transformations are
interpreted in terms of Chern-Simons equations of motion or, on the other hand,
as a consistency condition on the gauge. A mapping with a nonlinear
-model is discussed.Comment: 11 pages, Late
Online and offline heuristics for inferring hierarchies of repetitions in sequences
Hierarchical dictionary-based compression schemes form a grammar for a text by replacing each repeated string with a production rule. While such schemes usually operate online, making a replacement as soon as repetition is detected, offline operation permits greater freedom in choosing the order of replacement. In this paper, we compare the online method with three offline heuristics for selecting the next substring to replace: longest string first, most common string first, and the string that minimized the size of the grammar locally. Surprisingly, two of the offline techniques, like the online method, run in time linear in the size of the input. We evaluate each technique on artificial and natural sequences. In general, the locally-most-compressive heuristic performs best, followed by most frequent, the online technique, and, lagging by some distance, the longest-first technique
Detecting sequential structure
Programming by demonstration requires detection and analysis of sequential patterns in a user’s input, and the synthesis of an appropriate structural model that can be used for prediction. This paper describes SEQUITUR, a scheme for inducing a structural description of a sequence from a single example. SEQUITUR integrates several different inference techniques: identification of lexical subsequences or vocabulary elements, hierarchical structuring of such subsequences, identification of elements that have equivalent usage patterns, inference of programming constructs such as looping and branching, generalisation by unifying grammar rules, and the detection of procedural substructure., Although SEQUITUR operates with abstract sequences, a number of concrete illustrations are provided
Baryons and Flux Tubes in Confining Gauge Theories from Brane Actions
We study baryon configurations in large N non-supersymmetric SU(N) gauge
theories, applying the AdS/CFT correspondence. Using the D5-brane worldvolume
theory in the near-horizon geometry of non-extremal D3-branes, we find
embeddings which describe baryonic states in three-dimensional QCD. In
particular, we construct solutions corresponding to a baryon made of N quarks,
and study what happens when some fraction of the total number of quarks
are bodily moved to a large spatial separation from the others. The individual
clumps of quarks are represented by Born-Infeld string tubes obtained from a
D5-brane whose spatial section has topology . They are connected
by a confining color flux tube, described by a portion of the fivebrane that
runs very close and parallel to the horizon. We find that this flux tube has a
tension with a nontrivial -dependence (not previously obtained by other
methods). A similar picture is presented for the four-dimensional case.Comment: LaTeX, 20 pages, 6 eps figures; v2: added reference, corrected
numerical error in Eqs. (13) and (23
Heavy Quark Potential from Gauge/Gravity Duality: A Large D Analysis
The heavy-quark potential is calculated in the framework of gauge/gravity
duality using the large-D approximation, where D is the number of dimensions
transverse to the flux tube connecting a quark and an antiquark in a flat
D+2-dimensional spacetime. We find that in the large-D limit the leading
correction to the ground-state energy, as given by an effective Nambu-Goto
string, arises not from the heavy modes but from the behavior of the massless
modes in the vicinity of the quark and the antiquark. We estimate this
correction and find that it should be visible in the near-future lattice QCD
calculations of the heavy-quark potential.Comment: 22 pages, 5 Figures. v2: references added, typos corrected and, Sec.
4 rewritten with an expanded non-perturbative discussion of the corrections
to the Arvis potential arising from the massless modes near the boundary of
the qcd strin
Study of Bose-Einstein Correlations in e+e- -> W+W- events at LEP
Bose-Einstein correlation between like-sign charged-particle pairs in e+e- ->
W+W- events recorded with the OPAL detector at LEP at centre-of-mass energies
between 183 GeV and 209 GeV are studied. Recently proposed methods which allow
direct searches for correlations in the data via distributions of test
variables are used to investigate the presence of correlations between hadrons
originating from different W bosons in W+W- -> qqqq events. Within the
statistics of the data sample no evidence for inter-WW Bose-Einstein
correlations is obtained. The data are also compared with predictions of a
recent implementation of Bose-Einstein correlation effects in the Monte Carlo
model PYTHIA.Comment: 29 pages, 10 figures, Submitted to Eur. Phys. J.
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