667 research outputs found
Two-loop two-point functions with masses: asymptotic expansions and Taylor series, in any dimension
In all mass cases needed for quark and gluon self-energies, the two-loop
master diagram is expanded at large and small , in dimensions, using
identities derived from integration by parts. Expansions are given, in terms of
hypergeometric series, for all gluon diagrams and for all but one of the quark
diagrams; expansions of the latter are obtained from differential equations.
Pad\'{e} approximants to truncations of the expansions are shown to be of great
utility. As an application, we obtain the two-loop photon self-energy, for all
, and achieve highly accelerated convergence of its expansions in powers of
or , for .Comment: 25 pages, OUT--4102--43, BI--TP/92--5
Review of a Small-scale Pelagic Longline Fishery off Northeastern Brazil
The annual catches of four small longliners operating off northeast Brazil from 1983 to 1997 were examined across different areas and locations. The total catch comprised tunas (30%), sharks (54%), billfishes (12%), and other fish species (4%). Fishing strategy and annual composition of catches showed large spatial and temporal variabilities with the dominant catches alternating among yellowfin tuna,
Thunnus albacares; gray sharks, Carcharhinus spp.; and blue shark, Prionace glauca. Catches of blue and gray sharks
showed a significant interaction among seamounts, with gray sharks occurring in maximum abundance around those seamounts
that had relatively deep summits and low-sloping depth profiles. Results are discussed in terms of the various factors that may have influenced distribution of effort
Detecting the Gravitational Redshift of Cluster Gas
We examine the gravitational redshift of radiation emitted from within the
potential of a cluster. Spectral lines from the intracluster medium (ICM) are
redshifted in proportion to the emission-weighted mean potential along the line
of sight, amounting to approximately 50 km/s at a radius of 100 kpc/h, for a
cluster dispersion of 1200 km/s. We show that the relative redshifts of
different ionization states of metals in the ICM provide a unique probe of the
three-dimensional matter distribution. An examination of the reported peculiar
velocities of cD galaxies in well studied Abell clusters reveals they are
typically redshifted by an average of km/s. This can be achieved by
gravity with the addition of a steep central potential associated with the cD
galaxy. Note that in general gravitational redshifts cause a small overestimate
of the recessional velocities of clusters by an average of 20 km/s.Comment: 6 pages, 3 figures, accepted to the Astrophysical Journal Letter
Heavy-Light Meson Decay Constant from QCD Sum Rules in Three-Loop Approximation
In this paper we compute the decay constant of the pseudo-scalar heavy-light
mesons in the heavy quark effective theory framework of QCD sum rules. In our
analysis we include the recently evaluated three-loop result of order
for the heavy-light current correlator. The value of the bottom
quark mass, which essentially limits the accuracy of the sum rules for
meson, is extracted from the nonrelativistic sum rules for
resonances in the next-to-next-to-leading approximation. We find stability of
our result with respect to all types of corrections and the specific form of
the sum rule which reduces the uncertainty. Our results MeV and
MeV for the and meson decay constants are in impressive
agreement with recent lattice calculations.Comment: minor editorial changes, references added, to appear in PR
Second Order QCD Corrections to
Corrections of to the decay of the top quark into a W boson
and a bottom quark are calculated. The method is based on an expansion of the
top quark propagator for small external momentum, q, as compared to the top
quark mass, M_t. The physical point q^2 = M_t^2 is reached through Pad\'e
approximations. The described method allows to take effects induced by a finite
W boson mass into account. The numerical relevance of the result is discussed.
Important cross-checks against recent results for the decay rate and the two-loop QED corrections to -decay are performed.Comment: Latex, 21 pages, 1 figure included as ps-file. Minor changes;
reference added. Version to be published in PRD. The complete paper is also
available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-25/ or via www at
http://www-ttp.physik.uni-karlsruhe.de/Preprints
Current correlators to all orders in the quark masses
The contributions to the coefficient functions of the quark and the mixed
quark-gluon condensate to mesonic correlators are calculated for the first time
to all orders in the quark masses, and to lowest order in the strong coupling
constant. Existing results on the coefficient functions of the unit operator
and the gluon condensate are reviewed. The proper factorization of short- and
long-distance contributions in the operator product expansion is discussed in
detail. It is found that to accomplish this task rigorously the operator
product expansion has to be performed in terms of non-normal-ordered
condensates. The resulting coefficient functions are improved with the help of
the renormalization group. The scale invariant combination of dimension 5
operators, including mixing with the mass operator, which is needed for the
renormalization group improvement, is calculated in the leading order.Comment: 24 pages, LateX file, TUM-T31-21/92, 1 postscript file include
Singlet Polarization Functions at O(\alpha_s^2)
We consider the three-loop singlet diagrams induced by axial-vector, scalar
and pseudo-scalar currents. Expansions for small and large external momentum
are presented. They are used in combination with conformal mapping and
Pad\'e approximations in order to arrive at results for the polarization
functions valid for all . Results are presented for the imaginary parts
which are directly related to physical quantities like the production of top
quarks or the decay of scalar or pseudo-scalar Higgs bosons.Comment: LaTeX, 15 pages, 10 figures included as ps-files. The complete paper
is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/
, or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Phenomenology of Decays
Using the QCD sum rules technique we study several aspects of the
phenomenology of the b-flavoured strange meson . In particular, we
evaluate the mass of the particle, the leptonic constant and the form factors
of the decays , , . We also calculate, in the factorization approximation, a number of
two-body non leptonic decays.Comment: 19 pages, 2 figures (not included) available upon request, LaTex,
BARI-TH/93-139, UTS-DFT-93-1
Weighted sums with two parameters of multiple zeta values and their formulas
A typical formula of multiple zeta values is the sum formula which expresses
a Riemann zeta value as a sum of all multiple zeta values of fixed weight and
depth. Recently weighted sum formulas, which are weighted analogues of the sum
formula, have been studied by many people. In this paper, we give two formulas
of weighted sums with two parameters of multiple zeta values. As applications
of the formulas, we find some linear combinations of multiple zeta values which
can be expressed as polynomials of usual zeta values with coeffcients in the
rational polynomial ring generated by the two parameters, and obtain some
identities for weighted sums of multiple zeta values of small depths.Comment: 14 page
A 120-Mpc Periodicity in the Three-Dimensional Distribution of Galaxy Superclusters
Using a new compilation of available data on galaxy clusters and
superclusters we present evidence for a quasiregular three-dimensional network
of rich superclusters and voids, with the regions of high density separated by
about 120 Mpc. We calculate the power spectrum for clusters of galaxies; it has
a peak on the wavelength equal to the step of the network; the excess in the
amplitude of the spectrum over that of the cold dark matter model is by a
factor of 1.4. The probability that the spectrum can be formed within the
framework of the standard cosmogony is very small. If the cluster distribution
reflects the distribution of all matter (luminous and dark), then there must
exists some hithero unknown process that produces regular structure on large
scales.Comment: Tex, 6 pages, 2 PostScript figures embedded, accepted by Nature on
November 19, 199
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