2,398 research outputs found
Gluon Chain Model of the Confining Force
We develop a picture of the QCD string as a chain of constituent gluons,
bound by attractive nearest-neighbor forces which may be treated
perturbatively. This picture accounts for both Casimir scaling at large N, and
the asymptotic center dependence of the static quark potential. We discuss the
relevance, to the gluon-chain picture, of recent three-loop results for the
static quark potential. A variational framework is presented for computing the
minimal energy and wavefunction of a long gluon chain, which enables us to
derive both the logarithmic broadening of the QCD flux tube (``roughening''),
and the existence of a Luscher -c/R term in the potential.Comment: 25 pages, 5 figures, latex2
A theoretical study of microwave beam absorption by a rectenna
The rectenna's microwave power beam absorption limit was theoretically confirmed by two mathematical models descriptive of the microwave absorption process; first one model was based on the current sheet equivalency of a large planar array above a reflector and the second model, which was based on the properties of a waveguide with special imaging characteristics, quantified the electromagnetic modes (field configurations) in the immediate vicinity of a Rectenna element spacing which permit total power beam absorption by preventing unwanted modes from propagating (scattering) were derived using these models. Several factors causing unwanted scattering are discussed
Scattering of Glue by Glue on the Light-cone Worldsheet I: Helicity Non-conserving Amplitudes
We give the light-cone gauge calculation of the one-loop on-shell scattering
amplitudes for gluon-gluon scattering which violate helicity conservation. We
regulate infrared divergences by discretizing the p^+ integrations, omitting
the terms with p^+=0. Collinear divergences are absent diagram by diagram for
the helicity non-conserving amplitudes. We also employ a novel ultraviolet
regulator that is natural for the light-cone worldsheet description of planar
Feynman diagrams. We show that these regulators give the known answers for the
helicity non-conserving one-loop amplitudes, which don't suffer from the usual
infrared vagaries of massless particle scattering. For the maximal helicity
violating process we elucidate the physics of the remarkable fact that the loop
momentum integrand for the on-shell Green function associated with this
process, with a suitable momentum routing of the different contributing
topologies, is identically zero. We enumerate the counterterms that must be
included to give Lorentz covariant results to this order, and we show that they
can be described locally in the light-cone worldsheet formulation of the sum of
planar diagrams.Comment: 30 pages, 17 figure
Calculating the Rest Tension for a Polymer of String Bits
We explore the application of approximation schemes from many body physics,
including the Hartree-Fock method and random phase approximation (RPA), to the
problem of analyzing the low energy excitations of a polymer chain made up of
bosonic string bits. We accordingly obtain an expression for the rest tension
of the bosonic relativistic string in terms of the parameters
characterizing the microscopic string bit dynamics. We first derive an exact
connection between the string tension and a certain correlation function of the
many-body string bit system. This connection is made for an arbitrary
interaction potential between string bits and relies on an exact dipole sum
rule. We then review an earlier calculation by Goldstone of the low energy
excitations of a polymer chain using RPA. We assess the accuracy of the RPA by
calculating the first order corrections. For this purpose we specialize to the
unique scale invariant potential, namely an attractive delta function potential
in two (transverse) dimensions. We find that the corrections are large, and
discuss a method for summing the large terms. The corrections to this improved
RPA are roughly 15\%.Comment: 44 pages, phyzzx, psfig required, Univ. of Florida preprint,
UFIFT-HEP-94
Spontaneous Symmetry Breaking at Infinite Momentum without P+ Zero-Modes
The nonrelativistic interpretation of quantum field theory achieved by
quantization in an infinite momentum frame is spoiled by the inclusion of a
mode of the field carrying p+=0. We therefore explore the viability of doing
without such a mode in the context of spontaneous symmetry breaking (SSB),
where its presence would seem to be most needed. We show that the physics of
SSB in scalar quantum field theory in 1+1 space-time dimensions is accurately
described without a zero-mode.Comment: LaTeX, 8 pages, 3 eps figure
Scattering of Glue by Glue on the Light-cone Worldsheet II: Helicity Conserving Amplitudes
This is the second of a pair of articles on scattering of glue by glue, in
which we give the light-cone gauge calculation of the one-loop on-shell
helicity conserving scattering amplitudes for gluon-gluon scattering
(neglecting quark loops). The 1/p^+ factors in the gluon propagator are
regulated by replacing p^+ integrals with discretized sums omitting the p^+=0
terms in each sum. We also employ a novel ultraviolet regulator that is
convenient for the light-cone worldsheet description of planar Feynman
diagrams. The helicity conserving scattering amplitudes are divergent in the
infra-red. The infrared divergences in the elastic one-loop amplitude are shown
to cancel, in their contribution to cross sections, against ones in the cross
section for unseen bremsstrahlung gluons. We include here the explicit
calculation of the latter, because it assumes an unfamiliar form due to the
peculiar way discretization of p^+ regulates infrared divergences. In resolving
the infrared divergences we employ a covariant definition of jets, which allows
a transparent demonstration of the Lorentz invariance of our final results.
Because we use an explicit cutoff of the ultraviolet divergences in exactly 4
space-time dimensions, we must introduce explicit counterterms to achieve this
final covariant result. These counter-terms are polynomials in the external
momenta of the precise order dictated by power-counting. We discuss the
modifications they entail for the light-cone worldsheet action that reproduces
the ``bare'' planar diagrams of the gluonic sector of QCD. The simplest way to
do this is to interpret the QCD string as moving in six space-time dimensions.Comment: 56 pages, 21 figures, references added, minor typos correcte
-Dimensional Large QCD coupled to Adjoint Fermions
We consider 1+1-dimensional QCD coupled to Majorana fermions in the adjoint
representation of the gauge group . Pair creation of partons (fermion
quanta) is not suppressed in the large- limit, where the glueball-like bound
states become free. In this limit the spectrum is given by a linear \lc\ Schr\"
odinger equation, which we study numerically using the discretized \lcq. We
find a discrete spectrum of bound states, with the logarithm of the level
density growing approximately linearly with the mass. The wave function of a
typical excited state is a complicated mixture of components with different
parton numbers. A few low-lying states, however, are surprisingly close to
being eigenstates of the parton number, and their masses can be accurately
calculated by truncated diagonalizations.Comment: 22 pages + 9 figures (available by request from
[email protected]), uses phyzzx.tex + tables.tex PUPT-1413,
IASSNS-HEP-93/4
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Electrical capacitance tomography for flow imaging: System model for development of image reconstruction algorithms and design of primary sensors
A software tool that facilitates the development of image reconstruction algorithms, and the design of optimal capacitance sensors for a capacitance-based 12-electrode tomographic flow imaging system are described. The core of this software tool is the finite element (FE) model of the sensor, which is implemented in OCCAM-2 language and run on the Inmos T800 transputers. Using the system model, the in-depth study of the capacitance sensing fields and the generation of flow model data are made possible, which assists, in a systematic approach, the design of an improved image-reconstruction algorithm. This algorithm is implemented on a network of transputers to achieve a real-time performance. It is found that the selection of the geometric parameters of a 12-electrode sensor has significant effects on the sensitivity distributions of the capacitance fields and on the linearity of the capacitance data. As a consequence, the fidelity of the reconstructed images are affected. Optimal sensor designs can, therefore, be provided, by accommodating these effect
Increased Wellbeing following Engagement in a Group Nature-Based Programme: The Green Gym Programme Delivered by the Conservation Volunteers
The wellbeing benefits of engaging in a nature-based programme, delivered by the Voluntary, Community and Social Enterprise sector, were examined in this study. Prior to attending The Conservation Volunteers’ Green Gym™, attendees (n = 892) completed demographics, health characteristics and the Warwick Edinburgh Mental Wellbeing Short-Form Scale. Attendees (n = 253, 28.4%) provided a measure on average 4.5 months later. There were significant increases in wellbeing after engaging in Green Gym, with the greatest increases in those who had the lowest starting levels of wellbeing. Wellbeing increases were sustained on average 8.5 months and 13 months later in those providing a follow up measure (n = 92, n = 40, respectively). Attendees who continued to engage in Green Gym but not provide follow up data (n = 318, 35.7%) tended to be more deprived, female and self-report a health condition. Attendees who did not continue to engage in Green Gym (n = 321, 36.0%) tended to be less deprived and younger. These findings provide evidence of the wellbeing benefits of community nature-based activities and social (‘green’) prescribing initiatives and indicate that Green Gym targets some groups most in need
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