2,459 research outputs found
HQET chromomagnetic interaction at two loops
We present the coefficient of the chromomagnetic interaction operator, the
only unknown coefficient in the Heavy Quark Effective Theory (HQET) lagrangian
up to the level, with the two-loop accuracy by matching scattering
amplitudes of an on-shell heavy quark in an external field in full QCD and
HQET, and obtain the two-loop anomalous dimension of this operator in HQET.Comment: 10 pages, LaTeX2e, 2 eps figures included. Revised discussion of
(n_f-1)-flavour HQET include
Correlator of heavy-quark currents at small q^2 in the large-beta_0 limit
The correlator of vector heavy-quark currents at small q^2 is considered in
the large-beta_0 limit. The leading IR renormalon ambiguity of the sum of the
perturbative series is canceled by the UV renormalon ambiguity of the gluon
condensate. Asymptotic behaviour of the perturbative series is obtained in a
model-independent way, up to a single unknown normalization factor.
Gluon-virtuality distribution functions for the perturbative correction are
calculated.Comment: 8 pages, 3 figure
Mapping Cluster Mass Distributions via Gravitational Lensing of Background Galaxies
We present a new method for measuring the projected mass distributions of
galaxy clusters. The gravitational amplification is measured by comparing the
joint distribution in redshift and magnitude of galaxies behind the cluster
with that of field galaxies. We show that the total amplification is directly
related to the surface mass density in the weak field limit, and so it is
possible to map the mass distribution of the cluster. The method is shown to be
limited by discreteness noise and galaxy clustering behind the lens. Galaxy
clustering sets a lower limit to the error along the redshift direction, but a
clustering independent lensing signature may be obtained from the magnitude
distribution at fixed redshift. Statistical techniques are developed for
estimating the surface mass density of the cluster. We extend these methods to
account for any obscuration by cluster halo dust, which may be mapped
independently of the dark matter. We apply the method to a series of numerical
simulations and show the feasibility of the approach. We consider approximate
redshift information, and show how the mass estimates are degraded.Comment: ApJ in press. 23 pages of LaTeX plus figs. Text & figs available by
anonymous ftp from resun03.roe.ac.uk in directory /pub/jap/lens (you need
btp.tex and apj.sty
Using the Hopf Algebra Structure of QFT in Calculations
We employ the recently discovered Hopf algebra structure underlying
perturbative Quantum Field Theory to derive iterated integral representations
for Feynman diagrams. We give two applications: to massless Yukawa theory and
quantum electrodynamics in four dimensions.Comment: 28 p, Revtex, epsf for figures, minor changes, to appear in
Phys.Rev.
Higher loop renormalization of a supersymmetric field theory
Using Dyson--Schwinger equations within an approach developed by Broadhurst
and Kreimer and the renormalization group, we show how high loop order of the
renormalization group coefficients can be efficiently computed in a
supersymmetric model.Comment: 8 pages, 2 figure
On evaluation of two-loop self-energy diagram with three propogator
Small momentum expansion of the "sunset" diagram with three different masses
is obtained. Coefficients at powers of are evaluated explicitly in terms
of dilogarithms and elementary functions. Also some power expansions of
"sunset" diagram in terms of different sets of variables are given.Comment: 9 pages, LaTEX, MSU-PHYS-HEP-Lu3/9
Transcendental numbers and the topology of three-loop bubbles
We present a proof that all transcendental numbers that are needed for the
calculation of the master integrals for three-loop vacuum Feynman diagrams can
be obtained by calculating diagrams with an even simpler topology, the topology
of spectacles.Comment: 4 pages in REVTeX, 1 PostScript figure included, submitted to Phys.
Rev. Let
Analytical on-shell QED results: 3-loop vacuum polarization, 4-loop beta-function and the muon anomaly
We present the results of analytical calculations of the 3-loop contributions
to the asymptotic photon vacuum polarization function, in the on shell scheme,
and of the 4-loop contributions to the on shell QED beta-function. These are
used to evaluate various 4-loop and 5-loop contributions to the muon anomaly.
Our analytical contributions to (g-2)_\mu differ significantly from previous
numerical results. A very recent numerical re-evaluation of 4-loop muon-anomaly
contributions has yielded results much closer to ours.Comment: LaTex, 11 pages, figures available from O.V.T. CERN--TH. 6602/92,
OUT--4102--39, BI--TP--92/3
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