22,233 research outputs found
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
Critical velocity ionisation in substellar atmospheres
The observation of radio, X-ray and Hα emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterises Critical Velocity Ionisation, a potential ionisation process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a Gas-MHD interactions code (to simulate the ionisation mechanism) with a substellar global circulation model (to provide the required gas flows) we quantify the spatial extent of the resulting plasma regions, their degree of ionisation and their lifetime for a typical substellar atmosphere. It is found that the typical average ionisation fraction reached at equilibrium (where the ionisation and recombination rates are equal and opposite) ranges from 10-5 to 10-8, at pressures between 10-1 and 10-3 bar, with a trend of increasing ionisation fraction with decreasing atmospheric pressure. The ionisation fractions reached as a result of Critical Velocity Ionisation are sufficient to allow magnetic fields to couple to gas flows in the atmosphere
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
Classical String in Curved Backgrounds
The Mathisson-Papapetrou method is originally used for derivation of the
particle world line equation from the covariant conservation of its
stress-energy tensor. We generalize this method to extended objects, such as a
string. Without specifying the type of matter the string is made of, we obtain
both the equations of motion and boundary conditions of the string. The world
sheet equations turn out to be more general than the familiar minimal surface
equations. In particular, they depend on the internal structure of the string.
The relevant cases are classified by examining canonical forms of the effective
2-dimensional stress-energy tensor. The case of homogeneously distributed
matter with the tension that equals its mass density is shown to define the
familiar Nambu-Goto dynamics. The other three cases include physically relevant
massive and massless strings, and unphysical tahyonic strings.Comment: 12 pages, REVTeX 4. Added a note and one referenc
EFFICIENT ANALYTIC COMPUTATION OF HIGHER-ORDER QCD AMPLITUDES
We review techniques simplifying the analytic calculation of one-loop QCD
amplitudes with many external legs, for use in next-to-leading-order
corrections to multi-jet processes. Particularly useful are the constraints
imposed by perturbative unitarity, collinear singularities and a
supersymmetry-inspired organization of helicity amplitudes. Certain sequences
of one-loop helicity amplitudes with an arbitrary number of external gluons
have been obtained using these constraints.Comment: Talk given at Beyond the Standard Model IV, December 13-18 1994, Lake
Tahoe, CA. Latex, 4 pages, no figures
Cross-Order Relations in N=4 Supersymmetric Gauge Theories
The anti-de Sitter/conformal field theory duality conjecture raises the
question of how the perturbative expansion in the conformal field theory can
resum to a simple function. We exhibit a relation between the one-loop and
two-loop amplitudes whose generalization to higher-point and higher-loop
amplitudes would answer this question. We also provide evidence for the first
of these generalizations.Comment: 6 pages, talk given at the 3rd International Symposium on Quantum
Theory and Symmetries, Cincinnati, OH, Sept 10-14, 2003; v2: Mispositioned
figure in eqn. 1 fixe
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