184 research outputs found
Monodromy and Kawai-Lewellen-Tye Relations for Gravity Amplitudes
We are still learning intriguing new facets of the string theory motivated
Kawai-Lewellen-Tye (KLT) relations linking products of amplitudes in Yang-Mills
theories and amplitudes in gravity. This is very clearly displayed in
computations of N=8 supergravity where the perturbative expansion show a vast
number of similarities to that of N=4 super-Yang-Mills. We will here
investigate how identities based on monodromy relations for Yang-Mills
amplitudes can be very useful for organizing and further streamlining the KLT
relations yielding even more compact results for gravity amplitudes.Comment: 6 pages, 12th Marcel Grossman meeting 200
String theory and the KLT-relations between gravity and gauge theory including external matter
We consider the Kawai-Lewellen-Tye (KLT) factorizations of gravity scalar-leg
amplitudes into products of scalar-leg Yang-Mills amplitudes. We check and
examine the factorizations at O(1) in and extend the analysis by
considering KLT-mapping in the case of generic effective Lagrangians for
Yang-Mills theory and gravity.Comment: 7 pages, ReVTeX4, references updated, changes to text and typos
correcte
Explicit Cancellation of Triangles in One-loop Gravity Amplitudes
We analyse one-loop graviton amplitudes in the field theory limit of a
genus-one string theory computation. The considered amplitudes can be
dimensionally reduced to lower dimensions preserving maximal supersymmetry. The
particular case of the one-loop five-graviton amplitude is worked out in detail
and explicitly features no triangle contributions. Based on a recursive form of
the one-loop amplitude we investigate the contributions that will occur at
n-point order in relation to the ``no-triangle'' hypothesis of N=8
supergravity. We argue that the origin of unexpected cancellations observed in
gravity scattering amplitudes is linked to general coordinate invariance of the
gravitational action and the summation over all orderings of external legs.
Such cancellations are instrumental in the extraordinary good ultra-violet
behaviour of N=8 supergravity amplitudes and will play a central role in
improving the high-energy behaviour of gravity amplitudes at more than one
loop.Comment: 25 pages. 2 eps pictures, harvmac format. v2: version to appear in
JHEP. Equations (3.9), (3.12) and minor typos correcte
Absence of Triangles in Maximal Supergravity Amplitudes
From general arguments, we show that one-loop n-point amplitudes in
colourless theories satisfy a new type of reduction formula. These lead to the
existence of cancellations beyond supersymmetry. Using such reduction relations
we prove the no-triangle hypothesis in maximal supergravity by showing that in
four dimensions the n-point graviton amplitude contain only scalar box integral
functions. We also discuss the reduction formulas in the context of gravity
amplitudes with less and no supersymmetry.Comment: 23 pages, RevTeX4 format. v2: Expanded version with a new section
providing some extra background material and an overview of the general
arguments. Minors typos have been corrected. Version to be publishe
Gravitino Interactions from Yang-Mills Theory
We fabricate gravitino vertex interactions using as only input on-shell
Yang-Mills amplitudes and the Kawai-Lewellen-Tye gauge theory / gravity
relations. A useful result of this analysis is simpler tree-level Feynman rules
for gravitino scattering than in traditional gauges. All results are explicitly
verified until five point scattering.Comment: 17 pages, 10 figures, REVTe
String theory and the mapping of gravity into gauge theory
The relationship between on-shell tree level scattering amplitudes of open and closed strings, discovered some time ago by Kawai, Lewellen and Tye, is used at field theory level (at ) to establish a link between the general relativity and the non-abelian Yang-Mills effective actions. Insisting at the effective Lagrangian level that any tree point gravity on-shell scattering amplitude is directly factorisable into a sum of point left-right products of non-abelian Yang-Mills tree on-shell scattering amplitudes, non-trivial mappings of the effective general relativity operators into the effective non-abelian Yang-Mills operators are derived. Implications of such mapping relations of the field operators are discussed
Leading quantum gravitational corrections to scalar QED
We consider the leading post-Newtonian and quantum corrections to the non-relativistic scattering amplitude of charged scalars in the combined theory of general relativity and scalar QED. The combined theory is treated as an effective field theory. This allows for a consistent quantization of the gravitational field. The appropriate vertex rules are extracted from the action, and the non-analytic contributions to the 1-loop scattering matrix are calculated in the non-relativistic limit. The non-analytical parts of the scattering amplitude, which are known to give the long range, low energy, leading quantum corrections, are used to construct the leading post-Newtonian and quantum corrections to the two-particle non-relativistic scattering matrix potential for two charged scalars. The result is discussed in relation to experimental verifications
Leading quantum gravitational corrections to QED
We consider the leading post-Newtonian and quantum corrections to the
non-relativistic scattering amplitude of charged spin-1/2 fermions in the
combined theory of general relativity and QED. The coupled Dirac-Einstein
system is treated as an effective field theory. This allows for a consistent
quantization of the gravitational field. The appropriate vertex rules are
extracted from the action, and the non-analytic contributions to the 1-loop
scattering matrix are calculated in the non-relativistic limit. The
non-analytical parts of the scattering amplitude are known to give the long
range, low energy, leading quantum corrections, are used to construct the
leading post-Newtonian and quantum corrections to the two-particle
non-relativistic scattering matrix potential for two massive fermions with
electric charge.Comment: 14 pages, 29 figures, format RevTex
On-shell Techniques and Universal Results in Quantum Gravity
We compute the leading post-Newtonian and quantum corrections to the Coulomb
and Newtonian potentials using the full modern arsenal of on-shell techniques;
we employ spinor-helicity variables everywhere, use the Kawai-Lewellen-Tye
(KLT) relations to derive gravity amplitudes from gauge theory and use
unitarity methods to extract the terms needed at one-loop order. We stress that
our results are universal and thus will hold in any quantum theory of gravity
with the same low-energy degrees of freedom as we are considering. Previous
results for the corrections to the same potentials, derived historically using
Feynman graphs, are verified explicitly, but our approach presents a huge
simplification, since starting points for the computations are compact and
tedious index contractions and various complicated integral reductions are
eliminated from the onset, streamlining the derivations. We also analyze the
spin dependence of the results using the KLT factorization, and show how the
spinless correction in the framework are easily seen to be independent of the
interacting matter considered.Comment: 34 pages, 7 figures, typos corrected, published versio
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