587 research outputs found
On boundary RG-flows in coset conformal field theories
We propose a new rule for boundary renormalization group flows in fixed-point
free coset models. Our proposal generalizes the 'absorption of boundary
spin'-principle formulated by Affleck and Ludwig to a large class of
perturbations in boundary conformal field theories. We illustrate the rule in
the case of unitary minimal models.Comment: 3 pages, uses RevTeX
Representation Theory of Chern Simons Observables
Recently we suggested a new quantum algebra, the moduli algebra, which was
conjectured to be a quantum algebra of observables of the Hamiltonian Chern
Simons theory. This algebra provides the quantization of the algebra of
functions on the moduli space of flat connections on a 2-dimensional surface.
In this paper we classify unitary representations of this new algebra and
identify the corresponding representation spaces with the spaces of conformal
blocks of the WZW model. The mapping class group of the surface is proved to
act on the moduli algebra by inner automorphisms. The generators of these
automorphisms are unitary elements of the moduli algebra. They are constructed
explicitly and proved to satisfy the relations of the (unique) central
extension of the mapping class group.Comment: 63 pages, late
Brane dynamics in CFT backgrounds
In this note we discuss bound states of un- or meta-stable brane configurations in various non-trivial (curved) backgrounds. We begin by reviewing some known results concerning brane dynamics on group manifolds. These are then employed to study condensation in cosets of the WZW model. While the basic ideas are more general, our presentation focuses on parafermion theories and, closely related, superconformal minimal models. We determine the (non-commutative) low energy effective actions for all maximally symmetric branes in a decoupling limit of the two theories. These actions are used to show that the lightest branes can be regarded as elementary constituents for all other maximally symmetric branes
Heptagon Amplitude in the Multi-Regge Regime
As we have shown in previous work, the high energy limit of scattering
amplitudes in N=4 supersymmetric Yang-Mills theory corresponds to the infrared
limit of the 1-dimensional quantum integrable system that solves minimal area
problems in AdS5. This insight can be developed into a systematic algorithm to
compute the strong coupling limit of amplitudes in the multi-Regge regime
through the solution of auxiliary Bethe Ansatz equations. We apply this
procedure to compute the scattering amplitude for n=7 external gluons in
different multi-Regge regions at infinite 't Hooft coupling. Our formulas are
remarkably consistent with the expected form of 7-gluon Regge cut contributions
in perturbative gauge theory. A full description of the general algorithm and a
derivation of results will be given in a forthcoming paper.Comment: 14 page
Asymptotic boundary layer method for unstable trajectories : Semiclassical expansions for individual scar wavefunctions.
We extend the asymptotic boundary layer (ABL) method, originally developed for stable resonator modes, to the description of individual wave functions localized around unstable periodic orbits. The formalism applies to the description of scar states in fully or partially chaotic quantum systems, and also allows for the presence of smooth and sharp potentials, as well as magnetic fields. We argue that the separatrix wave function provides the largest contribution to the scars on a single wave function. This agrees with earlier results on the wave-function asymptotics and on the quantization condition of the scar states. Predictions of the ABL formalism are compared with the exact numerical solution for a strip resonator with a parabolic confinement potential and a magnetic field
Non-commutative World-volume Geometries: Branes on SU(2) and Fuzzy Spheres
The geometry of D-branes can be probed by open string scattering. If the
background carries a non-vanishing B-field, the world-volume becomes
non-commutative. Here we explore the quantization of world-volume geometries in
a curved background with non-zero Neveu-Schwarz 3-form field strength H = dB.
Using exact and generally applicable methods from boundary conformal field
theory, we study the example of open strings in the SU(2) Wess-Zumino-Witten
model, and establish a relation with fuzzy spheres or certain (non-associative)
deformations thereof. These findings could be of direct relevance for D-branes
in the presence of Neveu-Schwarz 5-branes; more importantly, they provide
insight into a completely new class of world-volume geometries.Comment: 19 pages, LaTeX, 1 figure; some explanations improved, references
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Brane Dynamics in Background Fluxes and Non-commutative Geometry
Branes in non-trivial backgrounds are expected to exhibit interesting
dynamical properties. We use the boundary conformal field theory approach to
study branes in a curved background with non-vanishing Neveu-Schwarz 3-form
field strength. For branes on an , the low-energy effective action is
computed to leading order in the string tension. It turns out to be a field
theory on a non-commutative `fuzzy 2-sphere' which consists of a Yang-Mills and
a Chern-Simons term. We find a certain set of classical solutions that have no
analogue for flat branes in Euclidean space. These solutions show, in
particular, how a spherical brane can arise as bound state from a stack of
D0-branes.Comment: 25 page
Counting statistics for mesoscopic conductors with internal degrees of freedom
We consider the transport of electrons passing through a mesoscopic device
possessing internal dynamical quantum degrees of freedom. The mutual
interaction between the system and the conduction electrons contributes to the
current fluctuations, which we describe in terms of full counting statistics.
We identify conditions where this discriminates coherent from incoherent
internal dynamics, and also identify and illustrate conditions under which the
device acts to dynamically bunch transmitted or reflected electrons, thereby
generating super-Poissonian noise.Comment: 4 pages, 2 figure
A Note on Noncommutative String theory and its low energy limit
The noncommutative string theory is described by embedding open string theory
in a constant second rank antisymmetric field and the
noncommutative gauge theory is defined by a deformed product. As a
check, study of various scattering amplitudes in both noncommutative string and
noncommutative gauge theory confirm that in the limit, the
noncommutative string theoretic amplitude goes over to the noncommutative gauge
theoretic amplitude, and the couplings are related as
. Furthermore we show that in this
limit there will not be any correction to the gauge theoretic action because of
absence of massive modes. We get sin/cos factors in the scattering amplitudes
depending on the odd/even number of external photons.Comment: 14 pages including 2 figure
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