14724506
Perturbative expansion in gauge theories on compact manifolds
A geometric formal method for perturbatively expanding functional integrals arising in quantum gauge theories is described when the spacetime is a compact riemannian manifold without boundary. This involves a refined version of the Faddeev-Popov procedure using the covariant background field gauge-fixing condition with background gauge field chosen to be a general critical point for the action functional (i.e. a classical solution). The refinement takes into account the gauge-fixing ambiguities coming from gauge transformations which leave the critical point unchanged, resulting in the absence of infrared divergences when the critical point is isolated modulo gauge transformations. The procedure can be carried out using only the subgroup of gauge transformations which are topologically trivial, possibly avoiding the usual problems which arise due to gauge-fixing ambiguities. For Chern-Simons gauge theory the method enables the partition function to be perturbatively expanded for a number of simple spacetime manifolds such as $S^3$ and lens spaces, and the expansions are shown to be formally independent of the metric used in the gauge-fixing.
8852930
Index of a family of lattice Dirac operators and its relation to the non-Abelian anomaly on the lattice.
In the continuum, a topological obstruction to the vanishing of the non-Abelian anomaly in 2n dimensions is given by the index of a certain Dirac operator in 2n+2 dimensions, or equivalently, the index of a 2-parameter family of Dirac operators in 2n dimensions. In this paper an analogous result is derived for chiral fermions on the lattice in the overlap formulation. This involves deriving an index theorem for a family of lattice Dirac operators satisfying the Ginsparg-Wilson relation. The index density is proportional to Lüscher's topological field in 2n+2 dimensions.
85538824
Dimensionally reduced expression for the QCD fermion determinant at finite temperature and chemical potential
A dimensionally reduced expression for the QCD fermion determinant at finite temperature and chemical potential is derived which sheds light on the determinant's dependence on these quantities. This is done via a partial zeta regularisation, formally applying a general formula for the zeta-determinant of a differential operator in one variable with operator-valued coefficients. The resulting expression generalises the known one for the free fermion determinant, obtained via Matsubara frequency summation, to the case of general background gauge field; moreover there is no undetermined overall factor. Rigorous versions of this result are obtained in a continuous time--lattice space setting. The determinant expression reduces to a remarkably simple form in the low temperature limit. A program for how to use this to obtain insight into the QCD phase transition at zero temperature and nonzero density is outlined.
14208386
Families index theory for Overlap lattice Dirac operator. I
Abstract The index bundle of the Overlap lattice Dirac operator over the orbit space of lattice gauge fields is introduced and studied. Obstructions to the vanishing of gauge anomalies in the Overlap formulation of lattice chiral gauge theory have a natural description in this context. Our main result is a formula for the topological charge (integrated Chern character) of the index bundle over even-dimensional spheres in the orbit space. It reduces under suitable conditions to the topological charge of the usual (continuum) index bundle in the classical continuum limit (this is announced and sketched here; the details will be given in a forthcoming paper). Thus we see that topology of the index bundle of the Dirac operator over the gauge field orbit space can be captured in a finite-dimensional lattice setting.
14198915
Partition function of a quadratic functional and semiclassical approximation for Witten's three manifold invariant
An extension of the method and results of A. Schwarz for evaluating the partition function of a quadratic functional is presented. This enables the partition functions to be evaluated for a wide class of quadratic functionals of interest in topological quantum field theory, for which no other method has previously been available. In particular it enables the partition functions appearing in the semiclassical approximation for the Witten-invariant to be evaluated in the most general case. The resulting k-dependence is precisely that conjectured by D. Freed and R. Gompf.
16500714
Phase and scaling properties of determinants arising in topological field theories
Abstract In topological field theory determinants of maps with negative as well as positive eigenvalues arise. We give a generalisation of the zeta-regularization technique to derive expressions for the phase and scaling-dependence of these determinants. For theories on odd-dimensional manifolds a simple formula for the scaling dependence is obtained in terms of the dimensions of cohomology spaces. This enables a non-perturbative feature of Chern-Simons gauge theory to be reproduced by semiclassical methods.
124601405
MUON IDENTIFICATION AND COMBINED RECONSTRUCTION FOR THE ATLAS DETECTOR AT CERN-LHC
121757543
Measurement of single spin asymmetry for direct photon production in pp collisions at 200 GeV/c
The single spin asymmetry for inclusive direct-photon production has been measured using a polarized proton beam of 200 GeV/c with an unpolarized proton target at −0.15 < xf < 0.15 and 2.5 < pt < 3.1 GeV/c at Fermilab. The data on the cross section for pp → γX at 2.5 < pt < 3.8 GeV/c are also provided. The measurement was done using lead-glass calorimeters and photon detectors which surrounded the fiducial area of the calorimeters. Background rejection has been done using these surrounding photon detectors. The cross section obtained is consistent with the results of previous measurements assuming a nuclear dependence of A1.0. The single spin asymmetry, AN, for the direct-photon production is consistent with zero within experimental uncertainty.
15397334
Improving the low-lying spectrum of the overlap kernel
Abstract The action of the overlap-Dirac operator on a vector is typically implemented indirectly through a multi-shift conjugate gradient solver. The compute-time this takes to evaluate depends upon the condition number κ of the matrix that is used as the overlap kernel. We examine the low-lying spectra of various candidate kernels in an effort to optimise κ, thereby speeding up the overlap evaluation.
71122772
Scintillating pad detectors
We have been investigating the performance of scintillating pad detectors, individual small tiles of scintillator that are read out with wavelength-shifting fibers and visible light photon counters, for application in high luminosity colliding beam experiments such as the DO Upgrade. Such structures could provide "pixel" type readout over large fiducial volumes for tracking, preshower detection and triggering.
13375438
ATLAS Distributed Analysis
The distributed analysis system for the ATLAS experiment is described. Although the system is under construction and the design is still evolving, the major components have been identified. A generic analysis service interface provides the connection between a choice of user environments and a selection of engines capable of carrying out the distributed processing. Other services provide access to catalogs, files and software.