12,844 research outputs found
Chiral Scale and Conformal Invariance in 2D Quantum Field Theory
It is well known that a local, unitary Poincare-invariant 2D QFT with a
global scaling symmetry and a discrete non-negative spectrum of scaling
dimensions necessarily has both a left and a right local conformal symmetry. In
this paper we consider a chiral situation beginning with only a left global
scaling symmetry and do not assume Lorentz invariance. We find that a left
conformal symmetry is still implied, while right translations are enhanced
either to a right conformal symmetry or a left U(1) Kac-Moody symmetry.Comment: 6 pages, no figures. v2: reference added, minor typos correcte
Deformations of Closed Strings and Topological Open Membranes
We study deformations of topological closed strings. A well-known example is
the perturbation of a topological closed string by itself, where the
associative OPE product is deformed, and which is governed by the WDVV
equations. Our main interest will be closed strings that arise as the boundary
theory for topological open membranes, where the boundary string is deformed by
the bulk membrane operators. The main example is the topological open membrane
theory with a nonzero 3-form field in the bulk. In this case the Lie bracket of
the current algebra is deformed, leading in general to a correction of the
Jacobi identity. We identify these deformations in terms of deformation theory.
To this end we describe the deformation of the algebraic structure of the
closed string, given by the BRST operator, the associative product and the Lie
bracket. Quite remarkably, we find that there are three classes of deformations
for the closed string, two of which are exemplified by the WDVV theory and the
topological open membrane. The third class remains largely mysterious, as we
have no explicit example.Comment: 50 pages, LaTeX; V2: minor changes, 2 references added, V3: typos
corrected, signs added, modified discussion on higher correlator
Einstein gravity from ANEC correlators
We study correlation functions with multiple averaged null energy (ANEC)
operators in conformal field theories. For large CFTs with a large gap to
higher spin operators, we show that the OPE between a local operator and the
ANEC can be recast as a particularly simple differential operator acting on the
local operator. This operator is simple enough that we can resum it and obtain
the finite distance OPE. Under the large - large gap assumptions, the
vanishing of the commutator of ANEC operators tightly constrains the OPE
coefficients of the theory. An important example of this phenomenon is the
conclusion that in . This implies that the bulk dual of such a CFT
is semi-classical Einstein-gravity with minimally coupled matter.Comment: 32 pages + appendices, 6 figures; v2:typos corrected and a comment
added in introductio
Warped Weyl fermion partition functions
Warped conformal field theories (WCFTs) are a novel class of non-relativistic
theories. A simple, yet non-trivial, example of such theory is a massive Weyl
fermion in -dimensions, which we study in detail. We derive general
properties of the spectrum and modular properties of partition functions of
WCFTs. The periodic (Ramond) sector of this fermionic system is non-trivial,
and we build two novel partition functions for this sector which have no
counterpart in a CFT. The thermodynamical properties of WCFTs are revisited
in the canonical and micro-canonical ensemble.Comment: 41 page
Black Holes, Entropy Bound and Causality Violation
The gravity/gauge theory duality has provided us a way of studying QCD at
short distances from straightforward calculations in classical general
relativity. Among numerous results obtained so far, one of the most striking is
the universality of the ratio of the shear viscosity to the entropy density.
For all gauge theories with Einstein gravity dual, this ratio is \eta/s=1/4\pi.
However, in general higher-curvature gravity theories, including two concrete
models under discussion - the Gauss-Bonnet gravity and the (Riemann)^2 gravity
- the ratio \eta/s can be smaller than 1/4\pi (thus violating the conjecture
bound), equal to 1/4\pi or even larger than 1/4\pi. As we probe spacetime at
shorter distances, there arises an internal inconsistency in the theory, such
as a violation of microcausality, which is correlated with a classical limit on
black hole entropy.Comment: 8 pages, no figures; Invited contribution to appear in the
Proceedings of the 75 Years since Solvay, Singapore, Nov 2008, (World
Scientific, Singapore, 2009
Context-Free Path Querying with Structural Representation of Result
Graph data model and graph databases are very popular in various areas such
as bioinformatics, semantic web, and social networks. One specific problem in
the area is a path querying with constraints formulated in terms of formal
grammars. The query in this approach is written as grammar, and paths querying
is graph parsing with respect to given grammar. There are several solutions to
it, but how to provide structural representation of query result which is
practical for answer processing and debugging is still an open problem. In this
paper we propose a graph parsing technique which allows one to build such
representation with respect to given grammar in polynomial time and space for
arbitrary context-free grammar and graph. Proposed algorithm is based on
generalized LL parsing algorithm, while previous solutions are based mostly on
CYK or Earley algorithms, which reduces time complexity in some cases.Comment: Evaluation extende
Generalized Lifshitz-Kosevich scaling at quantum criticality from the holographic correspondence
We characterize quantum oscillations in the magnetic susceptibility of a
quantum critical non-Fermi liquid. The computation is performed in a strongly
interacting regime using the nonperturbative holographic correspondence. The
temperature dependence of the amplitude of the oscillations is shown to depend
on a critical exponent nu. For general nu the temperature scaling is distinct
from the textbook Lifshitz-Kosevich formula. At the `marginal' value nu = 1/2,
the Lifshitz-Kosevich formula is recovered despite strong interactions. As a
by-product of our analysis we present a formalism for computing the amplitude
of quantum oscillations for general fermionic theories very efficiently.Comment: 18 pages, pdftex, 1 figure. v2: figure and few comments adde
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