3,113 research outputs found
Theoretical aspects of quantum electrodynamics in a finite volume with periodic boundary conditions
First-principles studies of strongly-interacting hadronic systems using
lattice quantum chromodynamics (QCD) have been complemented in recent years
with the inclusion of quantum electrodynamics (QED). The aim is to confront
experimental results with more precise theoretical determinations, e.g. for the
anomalous magnetic moment of the muon and the CP-violating parameters in the
decay of mesons. Quantifying the effects arising from enclosing QED in a finite
volume remains a primary target of investigations. To this end, finite-volume
corrections to hadron masses in the presence of QED have been carefully studied
in recent years. This paper extends such studies to the self-energy of moving
charged hadrons, both on and away from their mass shell. In particular, we
present analytical results for leading finite-volume corrections to the
self-energy of spin-0 and spin- particles in the presence of QED
on a periodic hypercubic lattice, once the spatial zero mode of the photon is
removed, a framework that is called . By altering
modes beyond the zero mode, an improvement scheme is introduced to eliminate
the leading finite-volume corrections to masses, with potential applications to
other hadronic quantities. Our analytical results are verified by a dedicated
numerical study of a lattice scalar field theory coupled to
. Further, this paper offers new perspectives on the
subtleties involved in applying low-energy effective field theories in the
presence of , a theory that is rendered non-local
with the exclusion of the spatial zero mode of the photon, clarifying recent
discussions on this matter.Comment: 57 pages, 10 figures, version accepted for publication in Phys. Rev.
Isolating a light Higgs boson from the di-photon background at the LHC
We compute the QCD corrections to the gluon fusion subprocess gg to gamma
gamma, which forms an important component of the background to the search for a
light Higgs boson at the LHC. We study the dependence of the improved pp to
gamma gamma X background calculation on the factorization and renormalization
scales, on various choices for photon isolation cuts, and on the rapidities of
the photons. We also investigate ways to enhance the statistical significance
of the Higgs signal in the di-photon channel.Comment: Additional reference included, 17 pages, 16 figure files, revte
Curvelet Approach for SAR Image Denoising, Structure Enhancement, and Change Detection
In this paper we present an alternative method for SAR image denoising, structure enhancement, and change detection based on the curvelet transform. Curvelets can be denoted as a two dimensional further development of the well-known wavelets. The original image is decomposed into linear ridge-like structures, that appear in different scales (longer or shorter structures), directions (orientation of the structure) and locations. The influence of these single components on the original image is weighted by the corresponding coefficients. By means of these coefficients one has direct access to the linear structures present in the image. To suppress noise in a given SAR image weak structures indicated by low coefficients can be suppressed by setting the corresponding coefficients to zero. To enhance structures only coefficients in the scale of interest are preserved and all others are set to zero. Two same-sized images assumed even a change detection can be done in the curvelet coefficient domain. The curvelet coefficients of both images are differentiated and manipulated in order to enhance strong and to suppress small scale (pixel-wise) changes. After the inverse curvelet transform the resulting image contains only those structures, that have been chosen via the coefficient manipulation. Our approach is applied to TerraSAR-X High Resolution Spotlight images of the city of Munich. The curvelet transform turns out to be a powerful tool for image enhancement in fine-structured areas, whereas it fails in originally homogeneous areas like grassland. In the change detection context this method is very sensitive towards changes in structures instead of single pixel or large area changes. Therefore, for purely urban structures or construction sites this method provides excellent and robust results. While this approach runs without any interaction of an operator, the interpretation of the detected changes requires still much knowledge about the underlying objects
Topological Signals of Singularities in Ricci Flow
We implement methods from computational homology to obtain a topological
signal of singularity formation in a selection of geometries evolved
numerically by Ricci flow. Our approach, based on persistent homology, produces
precise, quantitative measures describing the behavior of an entire collection
of data across a discrete sample of times. We analyze the topological signals
of geometric criticality obtained numerically from the application of
persistent homology to models manifesting singularities under Ricci flow. The
results we obtain for these numerical models suggest that the topological
signals distinguish global singularity formation (collapse to a round point)
from local singularity formation (neckpinch). Finally, we discuss the
interpretation and implication of these results and future applications.Comment: 24 pages, 14 figure
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