1,993 research outputs found
Skewed Sudakov Regime, Harmonic Numbers, and Multiple Polylogarithms
On the example of massless QED we study an asymptotic of the vertex when only
one of the two virtualities of the external fermions is sent to zero. We call
this regime the skewed Sudakov regime. First, we show that the asymptotic is
described with a single form factor, for which we derive a linear evolution
equation. The linear operator involved in this equation has a discrete
spectrum. Its eigenfunctions and eigenvalues are found. The spectrum is a
shifted sequence of harmonic numbers. With the spectrum found, we represent the
expansion of the asymptotic in the fine structure constant in terms of multiple
polylogarithms. Using this representation, the exponentiation of the doubly
logarithmic corrections of the Sudakov form factor is recovered. It is pointed
out that the form factor of the skewed Sudakov regime is growing with the
virtuality of a fermion decreasing at a fixed virtuality of another fermion.Comment: 6 page
The Challenge of Light-Front Quantisation: Recent Results
We explain what is the challenge of light-front quantisation, and how we can
now answer it because of recent progress in solving the problem of zero modes
in the case of non-Abelian gauge theories. We also give a description of the
light-front Hamiltonian for SU(2) finite volume gluodynamics resulting from
this recent solution to the problem of light-front zero modes.Comment: 17 pages, lecture delivered by GBP at the XXXIV PNPI Winter School,
Repino, St.Petersburg, Russia, February 14-20, 2000, version to appear in the
Proceeding
Phase composition, structure and properties of the spark plasma sintered ceramics obtained from the Al12Mg17-B-Si powder mixtures
In this work, composite materials were obtained by spark plasma sintering of an Al12Mg17-B-Si powder mixture. The structure, phase composition, and mechanical properties of the obtained composites were studied. It was found that various compounds based on B12 icosahedrons, such as AlB12, B4Si, and B6Si, are formed during spark plasma sintering. Based on the SEM images and results of XRD analysis of the obtained specimens, a probable scheme for the formation of the phase composition of composite materials during spark plasma sintering was proposed. An increase in the Al12Mg17-B powder content in the initial mixture from 30 to 70 wt% leads to an increase in hardness from 16.55 to 21.24 GPa and a decrease in the friction coefficient and wear rate from 0.56 to 0.32 and 13.60 to 5.60 10−5 mm−3/(N/m), respectively
Some New Results on Complex-Temperature Singularities in Potts Models on the Square Lattice
We report some new results on the complex-temperature (CT) singularities of
-state Potts models on the square lattice. We concentrate on the problematic
region (where ) in which CT zeros of the partition function
are sensitive to finite lattice artifacts. From analyses of low-temperature
series expansions for , we establish the existence, in this
region, of complex-conjugate CT singularities at which the magnetization and
susceptibility diverge. From calculations of zeros of the partition function,
we obtain evidence consistent with the inference that these singularities occur
at endpoints of arcs protruding into the (complex-temperature
extension of the) FM phase. Exponents for these singularities are determined;
e.g., for , we find , consistent with .
By duality, these results also imply associated arcs extending to the (CT
extension of the) symmetric PM phase. Analytic expressions are suggested for
the positions of some of these singularities; e.g., for , our finding is
consistent with the exact value . Further discussions of
complex-temperature phase diagrams are given.Comment: 26 pages, latex, with eight epsf figure
Canonical Formulation of the Light-Front Gluodynamics and Quantization of the Non-Abelian Plane Waves
Without a gauge fixing, canonical variables for the light-front SU(2)
gluodynamics are determined. The Gauss law is written in terms of the canonical
variables. The system is qualified as a generalized dynamical system with first
class constraints. Abeliazation is a specific feature of the formulation (most
of the canonical variables transform nontrivially only under the action of an
Abelian subgroup of the gauge transformations). At finite volume, a discrete
spectrum of the light-front Hamiltonian is obtained in the sector of
vanishing . We obtain, therefore, a quantized form of the classical
solutions previously known as non-Abelian plane waves. Then, considering the
infinite volume limit, we find that the presence of the mass gap depends on the
way the infinite volume limit is taken, which may suggest the presence of
different ``phases'' of the infinite volume theory. We also check that the
formulation obtained is in accord with the standard perturbation theory if the
latter is taken in the covariant gauges.Comment: REVTEX, 18 pages, version to appear in Phys. Rev.
Complex-Temperature Singularities in the Ising Model. III. Honeycomb Lattice
We study complex-temperature properties of the uniform and staggered
susceptibilities and of the Ising model on the honeycomb
lattice. From an analysis of low-temperature series expansions, we find
evidence that and both have divergent singularities at the
point (where ), with exponents
. The critical amplitudes at this
singularity are calculated. Using exact results, we extract the behaviour of
the magnetisation and specific heat at complex-temperature
singularities. We find that, in addition to its zero at the physical critical
point, diverges at with exponent , vanishes
continuously at with exponent , and vanishes
discontinuously elsewhere along the boundary of the complex-temperature
ferromagnetic phase. diverges at with exponent
and at (where ) with exponent , and
diverges logarithmically at . We find that the exponent relation
is violated at ; the right-hand side is 4
rather than 2. The connections of these results with complex-temperature
properties of the Ising model on the triangular lattice are discussed.Comment: 22 pages, latex, figures appended after the end of the text as a
compressed, uuencoded postscript fil
Dark sectors 2016 Workshop: community report
This report, based on the Dark Sectors workshop at SLAC in April 2016,
summarizes the scientific importance of searches for dark sector dark matter
and forces at masses beneath the weak-scale, the status of this broad
international field, the important milestones motivating future exploration,
and promising experimental opportunities to reach these milestones over the
next 5-10 years
Efficiency of Finding Muon Track Trigger Primitives in CMS Cathode Strip Chambers
In the CMS Experiment, muon detection in the forward direction is accomplished by cathode strip chambers~(CSC). These detectors identify muons, provide a fast muon trigger, and give a precise measurement of the muon trajectory. There are 468 six-plane CSCs in the system. The efficiency of finding muon trigger primitives (muon track segments) was studied using~36 CMS CSCs and cosmic ray muons during the Magnet Test and Cosmic Challenge~(MTCC) exercise conducted by the~CMS experiment in~2006. In contrast to earlier studies that used muon beams to illuminate a very small chamber area (~m), results presented in this paper were obtained by many installed CSCs operating {\em in situ} over an area of ~m as a part of the~CMS experiment. The efficiency of finding 2-dimensional trigger primitives within 6-layer chambers was found to be~. These segments, found by the CSC electronics within ~ns after the passing of a muon through the chambers, are the input information for the Level-1 muon trigger and, also, are a necessary condition for chambers to be read out by the Data Acquisition System
A genetic cause of Alzheimer disease: mechanistic insights from Down syndrome
Down syndrome, caused by an extra copy of chromosome 21, is associated with a greatly increased risk of early onset Alzheimer disease. It is thought that this risk is conferred by the presence of three copies of the gene encoding amyloid precursor protein (APP), an Alzheimer risk factor, although the possession of extra copies of other chromosome 21 genes may also play a role. Further study of the mechanisms underlying the development of Alzheimer disease in Down syndrome could provide insights into the mechanisms that cause dementia in the general population
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