1,633 research outputs found
A numerical test of differential equations for one- and two-loop sunrise diagrams using configuration space techniques
We use configuration space methods to write down one-dimensional integral
representations for one- and two-loop sunrise diagrams (also called Bessel
moments) which we use to numerically check on the correctness of the second
order differential equations for one- and two-loop sunrise diagrams that have
recently been discussed in the literature.Comment: 11 pages, no figures, published versio
Local and global duality and the determination of \alpha(M_Z)
This talk presents work concepts and results for the determination of the
fine structure constant at the mass resonance. The problem
consisting of the break-down of global duality for singular integral weights is
circumvented by using a polynomial fit which mimics this weight function. This
method is conservative in the sense that it is mostly independent of special
assumptions. In this context the difference between local and global duality is
explained.Comment: 8 pages in LaTeX using aipproc.cls (appended), 2 PostScript figures,
talk given at the conference High Energy Physics at the Millennium (MRST'99),
Ottawa, Canada, May 10-12, 1999, to appear in the proceeding
Analytical results for O(\alpha_s) radiative corrections to e+ e- -> tbar t(pol.) up to a given gluon energy cut
We determine the O(\alpha_s) radiative corrections to polarized top quark
pair production in e+ e- -annihilations with a specified gluon energy cut. We
write down fully analytical results for the unpolarized and polarized
O(\alpha_s) cross sections e+ e- -> tbar t (G) and e+ e- -> tbar t(pol.) (G)
including their polar orientation dependence relative to the beam direction. In
the soft gluon limit we recover the usual factorizing form known from the soft
gluon approximation. In the limit when the gluon energy cut takes its maximum
value we recover the totally inclusive unpolarized and polarized cross sections
calculated previously. We provide some numerical results on the cut-off
dependence of the various polarized and unpolarized cross sections and discuss
how the exact results numerically differ from the approximate soft-gluon
results.Comment: 49 pages in LaTeX, including 17 encapsulated PostScript figure
On the rigidity of back-to-back top quark pairs in e^+e^- annihilation
We consider the effect of gluon radiation on the energy of top/antitop quarks
and on the anticollinearity of top-antitop quark pairs produced in
annihilation. Our results are presented in terms of the -dependence of the
cross section and the dependence on the cosine of the opening angle
between top and antitop for a center of mass energy of
. We then go on to determine mean values for the top
quark's energy as well as its longitudinal and transverse projections, and for
the deviation of and from the
anticollinearity limits and . For a
center of mass energy of we obtain , and . Thus, at this energy gluon radiation causes a total
average energy loss of 0.71% of the top quark's energy. The average energy loss
in the longitudinal direction is 1.06% and the average energy gain in the
transverse direction is 1.88%. These percentage figures go up to 3.77%, 5.19%
and 6.06%, respectively, at 1000\GeV. For the mean of the acollinearity angle
we obtain at
, the value of which goes up to at . From an
analysis of the transverse momentum of the top we find that the mean transverse
momentum of the top stays close to the mean total momentum of the gluon in the
energy range from threshold to showing that the gluon momentum has a
large mean transverse component in this energy range.Comment: 17 pages, 7 postscript figures, to appear in Nucl. Phys.
Resolving the SELEX--LHCb Double-Charm Baryon Conflict: The Impact of Intrinsic Heavy-Quark Hadroproduction and Supersymmetric Light-Front Holographic QCD
In this paper we show that the intrinsic heavy-quark QCD mechanism for the
hadroproduction of heavy hadrons at large can resolve the apparent
conflict between measurements of double-charm baryons by the SELEX fixed-target
experiment and the LHCb experiment at the LHC collider. We show that both
experiments are compatible, and that both results can be correct. The observed
spectroscopy of double-charm hadrons is in agreement with the predictions of
supersymmetric light front holographic QCD.Comment: 15 pages, no figur
Heavy quark induced effective action for gauge fields in the SU(N_c) x U(1) model and the low-energy structure of heavy quark current correlators
We calculate the low-energy limit of heavy quark current correlators within
an expansion in the inverse heavy quark mass. The induced low-energy currents
built from the gluon fields corresponding to the initial heavy quark currents
are obtained from an effective action for gauge fields in the one-loop
approximation at the leading order of the 1/m expansion. Explicit formulae for
the low-energy spectra of electromagnetic and tensor heavy quark current
correlators are given. Consequences of the appearance of a nonvanishing
spectral density below the two-particle threshold for high precision
phenomenology of heavy quarks are discussed quantitatively.Comment: 21 pages in LaTeX, 2 PostScript figures included in the tex
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