16,612 research outputs found
Gluon Chain Model of the Confining Force
We develop a picture of the QCD string as a chain of constituent gluons,
bound by attractive nearest-neighbor forces which may be treated
perturbatively. This picture accounts for both Casimir scaling at large N, and
the asymptotic center dependence of the static quark potential. We discuss the
relevance, to the gluon-chain picture, of recent three-loop results for the
static quark potential. A variational framework is presented for computing the
minimal energy and wavefunction of a long gluon chain, which enables us to
derive both the logarithmic broadening of the QCD flux tube (``roughening''),
and the existence of a Luscher -c/R term in the potential.Comment: 25 pages, 5 figures, latex2
A New Algorithm for Protein Design
We apply a new approach to the reverse protein folding problem. Our method
uses a minimization function in the design process which is different from the
energy function used for folding. For a lattice model, we show that this new
approach produces sequences that are likely to fold into desired structures.
Our method is a significant improvement over previous attempts which used the
energy function for designing sequences.Comment: 10 pages latex 2.09 no figures. Use uufiles to decod
Partial regularity of almost minimizing rectifiable G chains in Hilbert space
We adapt to an infinite dimensional ambient space E.R. Reifenberg's
epiperimetric inequality and a quantitative version of D. Preiss' second
moments computations to establish that the set of regular points of an almost
mass minimizing rectifiable chain in is dense in its support,
whenever the group of coefficients is so that is
discrete and closed.Comment: 96 page
D-brane networks in flux vacua, generalized cycles and calibrations
We consider chains of generalized submanifolds, as defined by Gualtieri in
the context of generalized complex geometry, and define a boundary operator
that acts on them. This allows us to define generalized cycles and the
corresponding homology theory. Gauge invariance demands that D-brane networks
on flux vacua must wrap these generalized cycles, while deformations of
generalized cycles inside of a certain homology class describe physical
processes such as the dissolution of D-branes in higher-dimensional D-branes
and MMS-like instantonic transitions. We introduce calibrations that identify
the supersymmetric D-brane networks, which minimize their energy inside of the
corresponding homology class of generalized cycles. Such a calibration is
explicitly presented for type II N=1 flux compactifications to four dimensions.
In particular networks of walls and strings in compactifications on warped
Calabi-Yau's are treated, with explicit examples on a toroidal orientifold
vacuum and on the Klebanov-Strassler geometry.Comment: 42 pages, 4 eps figures, version to appear in JHE
Quantum Discord and entropic measures of quantum correlations: Optimization and behavior in finite spin chains
We discuss a generalization of the conditional entropy and one-way
information deficit in quantum systems, based on general entropic forms. The
formalism allows to consider simple entropic forms for which a closed
evaluation of the associated optimization problem in qudit-qubit systems is
shown to become feasible, allowing to approximate that of the quantum discord.
As application, we examine quantum correlations of spin pairs in the exact
ground state of finite spin chains in a magnetic field through the quantum
discord and information deficit. While these quantities show a similar
behavior, their optimizing measurements exhibit significant differences, which
can be understood and predicted through the previous approximations. The
remarkable behavior of these quantities in the vicinity of transverse and
non-transverse factorizing fields is also discussed.Comment: 10 pages, 3 figure
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