834 research outputs found
Next-to-leading order numerical calculations in Coulomb gauge
Calculations of observables in quantum chromodynamics can be performed using
a method in which all of the integrations, including integrations over virtual
loop momenta, are performed numerically. We use the flexibility inherent in
this method in order to perform next-to-leading order calculations for event
shape variables in electron-positron annihilation in Coulomb gauge. The use of
Coulomb gauge provides the potential to go beyond a purely order alpha_s^2
calculation by including, for instance, renormalon or parton showering effects.
We expect that the approximations needed to include such effects at all orders
in alpha_s will be simplest in a gauge in which unphysically polarized gluons
do not propagate over long distances.Comment: 36 pages with 7 figure
Choosing integration points for QCD calculations by numerical integration
I discuss how to sample the space of parton momenta in order to best perform
the numerical integrations that lead to a calculation of three jet cross
sections and similar observables in electron-positron annihilation.Comment: 25 pages with 8 figure
General subtraction method for numerical calculation of one-loop QCD matrix elements
We present a subtraction scheme for eliminating the ultraviolet, soft, and
collinear divergences in the numerical calculation of an arbitrary one-loop QCD
amplitude with an arbitrary number of external legs. The subtractions consist
of local counter terms in the space of the four-dimensional loop momentum. The
ultraviolet subtraction terms reproduce MSbar renormalization. The key point in
the method for the soft and collinear subtractions is that, although the
subtraction terms are defined graph-by-graph and the matrix element is also
calculated graph-by-graph, the sum over graphs of the integral of each the
subtraction term can be evaluated analytically and provides the well known
simple pole structure that arises from subtractions from real emission graphs,
but with the opposite sign.Comment: 38 pages, 10 figures, axodraw styl
Hadronic Probes of the Polarized Intrinsic Strangeness of the Nucleon
We have previously interpreted the various large apparent violations of the naive Okubo-Zweig-Iizuka (OZI) rule found in many channels in annihilation at LEAR as evidence for an intrinsic polarized component of the nucleon wave function. The model is further supported by new data from LEAR and elsewhere. Here we discuss in more detail the possible form of the component of the nucleon wave function, interpret the new data and clarify the relative roles of strangeness shake-out and rearrangement, discuss whether alternative interpretations are still allowed by the new data, and propose more tests of the model.We have previously interpreted the various large apparent violations of the naive Okubo-Zweig-Iizuka (OZI) rule found in many channels in annihilation at LEAR as evidence for an intrinsic polarized component of the nucleon wave function. The model is further supported by new data from LEAR and elsewhere. Here we discuss in more detail the possible form of the component of the nucleon wave function, interpret the new data and clarify the relative roles of strangeness shake-out and rearrangement, discuss whether alternative interpretations are still allowed by the new data, and propose more tests of the model.We have previously interpreted the various large apparent violations of the naive Okubo-Zweig-Iizuka (OZI) rule found in many channels in annihilation at LEAR as evidence for an intrinsic polarized component of the nucleon wave function. The model is further supported by new data from LEAR and elsewhere. Here we discuss in more detail the possible form of the component of the nucleon wave function, interpret the new data and clarify the relative roles of strangeness shake-out and rearrangement, discuss whether alternative interpretations are still allowed by the new data, and propose more tests of the model.We have previously interpreted the various large apparent violations of the naive Okubo-Zweig-Iizuka (OZI) rule found in many channels in annihilation at LEAR as evidence for an intrinsic polarized component of the nucleon wave function. The model is further supported by new data from LEAR and elsewhere. Here we discuss in more detail the possible form of the component of the nucleon wave function, interpret the new data and clarify the relative roles of strangeness shake-out and rearrangement, discuss whether alternative interpretations are still allowed by the new data, and propose more tests of the model.We have previously interpreted the various large apparent violations of the naıÌve OkuboâZweigâIizuka (OZI) rule found in many channels in p Ì p annihilation at LEAR as evidence for an intrinsic polarized s Ì s component of the nucleon wave function. The model is further supported by new data from LEAR and elsewhere. Here we discuss in more detail the possible form of the s Ì s component of the nucleon wave function, interpret the new data and clarify the relative roles of strangeness shake-out and rearrangement, discuss whether alternative interpretations are still allowed by the new data, and propose more tests of the model
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Theoretical studies of defects in binary and ternary oxides
This paper presents some preliminary results of electronic structure of substitutional defects and vacancy in binary and ternary cubic zirconium oxides obtained by the embedded molecular-cluster model calculation. The importance of electronic charge redistribution in the solids where the defect is introduced into the perfect lattice is highlighted and the effect of electron polarization of the surrounding ions of the defect discussed
Hadronic Probes of the Polarized Intrinsic Strangeness of the Nucleon
We have previously interpreted the various large apparent violations of the
naive Okubo-Zweig-Iizuka (OZI) rule found in many channels in
annihilation at LEAR as evidence for an intrinsic polarized
component of the nucleon wave function. The model is further supported by new
data from LEAR and elsewhere. Here we discuss in more detail the possible form
of the component of the nucleon wave function, interpret the new
data and clarify the relative roles of strangeness shake-out and rearrangement,
discuss whether alternative interpretations are still allowed by the new data,
and propose more tests of the model.Comment: LaTeX, 31 page
Structure of Fat Jets at the Tevatron and Beyond
Boosted resonances is a highly probable and enthusiastic scenario in any
process probing the electroweak scale. Such objects when decaying into jets can
easily blend with the cornucopia of jets from hard relative light QCD states.
We review jet observables and algorithms that can contribute to the
identification of highly boosted heavy jets and the possible searches that can
make use of such substructure information. We also review previous studies by
CDF on boosted jets and its measurements on specific jet shapes.Comment: invited review for a special "Top and flavour physics in the LHC era"
issue of The European Physical Journal C, we invite comments regarding
contents of the review; v2 added references and institutional preprint
number
Study of the dependence of 198Au half-life on source geometry
We report the results of an experiment to determine whether the half-life of
\Au{198} depends on the shape of the source. This study was motivated by recent
suggestions that nuclear decay rates may be affected by solar activity, perhaps
arising from solar neutrinos. If this were the case then the -decay
rates, or half-lives, of a thin foil sample and a spherical sample of gold of
the same mass and activity could be different. We find for \Au{198},
, where
is the mean half-life. The maximum neutrino flux at the sample in our
experiments was several times greater than the flux of solar neutrinos at the
surface of the Earth. We show that this increase in flux leads to a significant
improvement in the limits that can be inferred on a possible solar contribution
to nuclear decays.Comment: 5 pages, 1 figur
Can multi-TeV (top and other) squarks be natural in gauge mediation?
We investigate whether multi-TeV (1-3 TeV) squarks can be natural in models
of gauge mediated SUSY breaking. The idea is that for some boundary condition
of the scalar (Higgs and stop) masses, the Higgs (mass), evaluated at the
renormalization scale GeV, is not very sensitive to (boundary
values of) the scalar masses (this has been called ``focussing'' in recent
literature). Then, the stop masses can be multi-TeV without leading to
fine-tuning in electroweak symmetry breaking. {\em Minimal} gauge mediation
does {\em not} lead to this focussing (for all values of and the
messenger scale): the (boundary value of) the Higgs mass is too small compared
to the stop masses. Also, in minimal gauge mediation, the gaugino masses are of
the same order as the scalar masses so that multi-TeV scalars implies multi-TeV
gauginos (especially gluino) leading to fine-tuning. We discuss ideas to {\em
increase} the Higgs mass relative to the stop masses (so that focussing can be
achieved) and also to {\em suppress} gaugino masses relative to scalar masses
(or to modify the gaugino mass relations) in {\em non-minimal} models of gauge
mediation -- then multi-TeV (top and other) squarks can be natural. Specific
models of gauge mediation which incorporate these ideas and thus have squarks
(and in some cases, the gluino) heavier than a TeV without resulting in
fine-tuning are also studied and their collider signals are contrasted with
those of other models which have multi-TeV squarks.Comment: LaTeX, 29 pages, 9 eps figures. Replacing an earlier version. In
version 3, some references and a minor comment have been added and typos have
been correcte
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