2,226 research outputs found
Calculation of 1-loop Hexagon Amplitudes in the Yukawa Model
We calculate a class of one-loop six-point amplitudes in the Yukawa model.
The construction of multi-particle amplitudes is done in the string inspired
formalism and compared to the Feynman diagrammatic approach. We show that there
exists a surprisingly efficient way of calculating such amplitudes by using
cyclic identities of kinematic coefficients and discuss in detail cancellation
mechanisms of spurious terms. A collection of formulas which are useful for the
calculation of massless hexagon amplitudes is given.Comment: 15 pages Late
Next-to-Maximal Helicity Violating Amplitudes in Gauge Theory
Using the novel diagrammatic rules recently proposed by Cachazo, Svrcek, and
Witten, I give a compact, manifestly Lorentz-invariant form for tree-level
gauge-theory amplitudes with three opposite helicities.Comment: 12 pages, 1 figur
On the Coupling of Gravitons to Matter
Using relationships between open and closed strings, we present a
construction of tree-level scattering amplitudes for gravitons minimally
coupled to matter in terms of gauge theory partial amplitudes. In particular,
we present examples of amplitudes with gravitons coupled to vectors or to a
single fermion pair. We also present two examples with massive graviton
exchange, as would arise in the presence of large compact dimensions. The gauge
charges are represented by flavors of dynamical scalars or fermions. This also
leads to an unconventional decomposition of color and kinematics in gauge
theories.Comment: RevTex, 4 page
The Five Gluon Amplitude and One-Loop Integrals
We review the conventional field theory description of the string motivated
technique. This technique is applied to the one-loop five-gluon amplitude. To
evaluate the amplitude a general method for computing dimensionally regulated
one-loop integrals is outlined including results for one-loop integrals
required for the pentagon diagram and beyond. Finally, two five-gluon helicity
amplitudes are given.Comment: (talk presented at DPF92), LaTeX, 6 pages, CERN-Th.6733/92,
SLAC-PUB-6012, UCLA/92/TEP/4
A technique for loop calculations in non-Abelian gauge theories - with application to five gluon amplitude
A powerful tool for calculations in non-Abelian gauge theories is obtained by
combining the background field gauge, the helicity basis and the color
decomposition methods. It has reproduced the one-loop calculation of the
five-gluon amplitudes in QCD, is applicable to electroweak processes and
extendable to two-loop calculations.Comment: Latex 22 pages, 3 figure
S@M, a Mathematica Implementation of the Spinor-Helicity Formalism
In this paper we present the package S@M (Spinors@Mathematica) which
implements the spinor-helicity formalism in Mathematica. The package allows the
use of complex-spinor algebra along with the multi-purpose features of
Mathematica. The package defines the spinor objects with their basic properties
along with functions to manipulate them. It also offers the possibility of
evaluating the spinorial objects numerically at every computational step. The
package is therefore well suited to be used in the context of on-shell
technology, in particular for the evaluation of scattering amplitudes at tree-
and loop-level.Comment: 52 pages, the package can be downloaded from
http://www.slac.stanford.edu/grp/th/software/#Mathematica_Packages
Three Applications of the String-Inspired Technique to Quantum Electrodynamics
We discuss the following recent applications of the ``string-inspired''
worldline technique to calculations in quantum electrodynamics: i) Photon
splitting in a constant magnetic field, ii) The two-loop Euler-Heisenberg
Lagrangian, iii) A progress report on a recalculation of the three-loop QED
beta -- function.Comment: 10 pages, uuencoded Postscript-File, talk given by C. Schubert at the
Zeuthen Workshop on Elementary Particle Theory: QCD and QED in Higher Orders,
Rheinsberg, Germany, 21-26 Apr 199
One-Loop Self-Dual and N=4 Super Yang-Mills
We conjecture a simple relationship between the one-loop maximally helicity
violating gluon amplitudes of ordinary QCD (all helicities identical) and those
of N=4 supersymmetric Yang-Mills (all but two helicities identical). Because
the amplitudes in self-dual Yang Mills have been shown to be the same as the
maximally helicity violating ones in QCD, this conjecture implies that they are
also related to the maximally helicity violating ones of N=4 supersymmetric
Yang-Mills. We have an explicit proof of the relation up to the six-point
amplitude; for amplitudes with more external legs, it remains a conjecture. A
similar conjecture relates amplitudes in self-dual gravity to maximally
helicity violating N=8 supergravity amplitudes.Comment: 14 pages, TeX, three figures, two new references adde
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