2,199 research outputs found
Coordinate representation of particle dynamics in AdS and in generic static spacetimes
We discuss the quantum dynamics of a particle in static curved spacetimes in
a coordinate representation. The scheme is based on the analysis of the squared
energy operator E^2, which is quadratic in momenta and contains a scalar
curvature term. Our main emphasis is on AdS spaces, where this term is fixed by
the isometry group. As a byproduct the isometry generators are constructed and
the energy spectrum is reproduced. In the massless case the conformal symmetry
is realized as well. We show the equivalence between this quantization and the
covariant quantization, based on the Klein-Gordon type equation in AdS. We
further demonstrate that the two quantization methods in an arbitrary
(N+1)-dimensional static spacetime are equivalent to each other if the scalar
curvature terms both in the operator E^2 and in the Klein-Gordon type equation
have the same coefficient equal to (N-1)/(4N).Comment: 14 pages, no figures, typos correcte
An Exact Algorithm for TSP in Degree-3 Graphs via Circuit Procedure and Amortization on Connectivity Structure
The paper presents an O^*(1.2312^n)-time and polynomial-space algorithm for
the traveling salesman problem in an n-vertex graph with maximum degree 3. This
improves the previous time bounds of O^*(1.251^n) by Iwama and Nakashima and
O^*(1.260^n) by Eppstein. Our algorithm is a simple branch-and-search
algorithm. The only branch rule is designed on a cut-circuit structure of a
graph induced by unprocessed edges. To improve a time bound by a simple
analysis on measure and conquer, we introduce an amortization scheme over the
cut-circuit structure by defining the measure of an instance to be the sum of
not only weights of vertices but also weights of connected components of the
induced graph.Comment: 24 pages and 4 figure
Recent Greenland accumulation estimated from regional climate model simulations and ice core analysis
Loop Equation in Two-dimensional Noncommutative Yang-Mills Theory
The classical analysis of Kazakov and Kostov of the Makeenko-Migdal loop
equation in two-dimensional gauge theory leads to usual partial differential
equations with respect to the areas of windows formed by the loop. We extend
this treatment to the case of U(N) Yang-Mills defined on the noncommutative
plane. We deal with all the subtleties which arise in their two-dimensional
geometric procedure, using where needed results from the perturbative
computations of the noncommutative Wilson loop available in the literature. The
open Wilson line contribution present in the non-commutative version of the
loop equation drops out in the resulting usual differential equations. These
equations for all N have the same form as in the commutative case for N to
infinity. However, the additional supplementary input from factorization
properties allowing to solve the equations in the commutative case is no longer
valid.Comment: 20 pages, 3 figures, references added, small clarifications adde
Halocarbon ozone depletion and global warming potentials
Concern over the global environmental consequences of fully halogenated chlorofluorocarbons (CFCs) has created a need to determine the potential impacts of other halogenated organic compounds on stratospheric ozone and climate. The CFCs, which do not contain an H atom, are not oxidized or photolyzed in the troposphere. These compounds are transported into the stratosphere where they decompose and can lead to chlorine catalyzed ozone depletion. The hydrochlorofluorocarbons (HCFCs or HFCs), in particular those proposed as substitutes for CFCs, contain at least one hydrogen atom in the molecule, which confers on these compounds a much greater sensitivity toward oxidation by hydroxyl radicals in the troposphere, resulting in much shorter atmospheric lifetimes than CFCs, and consequently lower potential for depleting ozone. The available information is reviewed which relates to the lifetime of these compounds (HCFCs and HFCs) in the troposphere, and up-to-date assessments are reported of the potential relative effects of CFCs, HCFCs, HFCs, and halons on stratospheric ozone and global climate (through 'greenhouse' global warming)
Quantum-Gravitational Diffusion and Stochastic Fluctuations in the Velocity of Light
We argue that quantum-gravitational fluctuations in the space-time background
give the vacuum non-trivial optical properties that include diffusion and
consequent uncertainties in the arrival times of photons, causing stochastic
fluctuations in the velocity of light ``in vacuo''. Our proposal is motivated
within a Liouville string formulation of quantum gravity that also suggests a
frequency-dependent refractive index of the particle vacuum. We construct an
explicit realization by treating photon propagation through quantum excitations
of -brane fluctuations in the space-time foam. These are described by
higher-genus string effects, that lead to stochastic fluctuations in couplings,
and hence in the velocity of light. We discuss the possibilities of
constraining or measuring photon diffusion ``in vacuo'' via -ray
observations of distant astrophysical sources.Comment: 17 pages LATEX, uses axodraw style fil
Seiberg-Witten maps and noncommutative Yang-Mills theories for arbitrary gauge groups
Seiberg-Witten maps and a recently proposed construction of noncommutative
Yang-Mills theories (with matter fields) for arbitrary gauge groups are
reformulated so that their existence to all orders is manifest. The ambiguities
of the construction which originate from the freedom in the Seiberg-Witten map
are discussed with regard to the question whether they can lead to inequivalent
models, i.e., models not related by field redefinitions.Comment: 12 pages; references added, minor misprints correcte
Liouville Correlation Functions from Four-dimensional Gauge Theories
We conjecture an expression for the Liouville theory conformal blocks and
correlation functions on a Riemann surface of genus g and n punctures as the
Nekrasov partition function of a certain class of N=2 SCFTs recently defined by
one of the authors. We conduct extensive tests of the conjecture at genus 0,1.Comment: 32 pages, 8 figures; v2: minor corrections, published versio
Electron impact double ionization of helium from classical trajectory calculations
With a recently proposed quasiclassical ansatz [Geyer and Rost, J. Phys. B 35
(2002) 1479] it is possible to perform classical trajectory ionization
calculations on many electron targets. The autoionization of the target is
prevented by a M\o{}ller type backward--forward propagation scheme and allows
to consider all interactions between all particles without additional
stabilization. The application of the quasiclassical ansatz for helium targets
is explained and total and partially differential cross sections for electron
impact double ionization are calculated. In the high energy regime the
classical description fails to describe the dominant TS1 process, which leads
to big deviations, whereas for low energies the total cross section is
reproduced well. Differential cross sections calculated at 250 eV await their
experimental confirmation.Comment: LaTeX, 22 pages, 10 figures, submitted to J. Phys.
On the invariance under area preserving diffeomorphisms of noncommutative Yang-Mills theory in two dimensions
We present an investigation on the invariance properties of noncommutative
Yang-Mills theory in two dimensions under area preserving diffeomorphisms.
Stimulated by recent remarks by Ambjorn, Dubin and Makeenko who found a
breaking of such an invariance, we confirm both on a fairly general ground and
by means of perturbative analytical and numerical calculations that indeed
invariance under area preserving diffeomorphisms is lost. However a remnant
survives, namely invariance under linear unimodular tranformations.Comment: LaTeX JHEP style, 16 pages, 2 figure
- …