2,059 research outputs found
On Perturbative Gravity and Gauge Theory
We review some applications of tree-level (classical) relations between
gravity and gauge theory that follow from string theory. Together with
-dimensional unitarity, these relations can be used to perturbatively
quantize gravity theories, i.e. they contain the necessary information for
obtaining loop contributions. We also review recent applications of these ideas
showing that N=1 D=11 supergravity diverges, and review arguments that N=8 D=4
supergravity is less divergent than previously thought, though it does appear
to diverge at five loops. Finally, we describe field variables for the
Einstein-Hilbert Lagrangian that help clarify the perturbative relationship
between gravity and gauge theory.Comment: Talk presented at Third Meeting on Constrained Dynamics and Quantum
Gravity, Villasimius (Sardinia, Italy) September 13-17, 1999 and at the
Workshop on Light-Cone QCD and Nonperturbative Hadron Physics, University of
Adelaide (Australia) December 13-22, 1999. Latex, 9 page
Two-Loop -Diagrams from String Theory
Using the {\em cutting and sewing} procedure we show how to get Feynman
diagrams, up to two-loop order, of -theory with an internal SU(N)
symmetry group, starting from tachyon amplitudes of the open bosonic string
theory. In a properly defined field theory limit, we easily identify the
corners of the string moduli space reproducing the correctly normalized field
theory amplitudes expressed in the Schwinger parametrization.Comment: 28 pages, 12 figure
Multi-Leg One-Loop Gravity Amplitudes from Gauge Theory
By exploiting relations between gravity and gauge theories, we present two
infinite sequences of one-loop n-graviton scattering amplitudes: the `maximally
helicity-violating' amplitudes in N=8 supergravity, and the `all-plus' helicity
amplitudes in gravity with any minimally coupled massless matter content. The
all-plus amplitudes correspond to self-dual field configurations and vanish in
supersymmetric theories. We make use of the tree-level Kawai-Lewellen-Tye (KLT)
relations between open and closed string theory amplitudes, which in the
low-energy limit imply relations between gravity and gauge theory tree
amplitudes. For n < 7, we determine the all-plus amplitudes explicitly from
their unitarity cuts. The KLT relations, applied to the cuts, allow us to
extend to gravity a previously found `dimension-shifting' relation between (the
cuts of) the all-plus amplitudes in gauge theory and the maximally
helicity-violating amplitudes in N=4 super-Yang-Mills theory. The gravitational
version of the relation lets us determine the n < 7 N=8 supergravity amplitudes
from the all-plus gravity amplitudes. We infer the two series of amplitudes for
all n from their soft and collinear properties, which can also be derived from
gauge theory using the KLT relations.Comment: Minor errors corrected, Latex, 53 page
One-Loop n-Point Helicity Amplitudes in (Self-Dual) Gravity
We present an ansatz for all one-loop amplitudes in pure Einstein gravity for
which the n external gravitons have the same outgoing helicity. These loop
amplitudes, which are rational functions of the momenta, also arise in the
quantization of self-dual gravity in four-dimensional Minkowski space. Our
ansatz agrees with explicit computations via D-dimensional unitarity cuts for n
less than or equal to 6. It also has the expected analytic behavior, for all n,
as a graviton becomes soft, and as two momenta become collinear. The gravity
results are closely related to analogous amplitudes in (self-dual) Yang-Mills
theory.Comment: Latex2e, 13 pages with 2 encapsulated figures. Minor corrections mad
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
Perturbative Relations between Gravity and Gauge Theory
We review the relations that have been found between multi-loop scattering
amplitudes in gauge theory and gravity, and their implications for ultraviolet
divergences in supergravity.Comment: LaTex with package axodraw.sty. 10 pages. Presented by L.D. at
Strings 99. Cosmetic changes onl
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
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