1,953 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
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
Hydrodynamics of a quark droplet II: Implications of a non-zero baryon chemical potential
We present an extended version of the dynamical model for a multi-quark
droplet evolution described in our proceeding paper. The model includes
collective expansion of the droplet, effects of the vacuum pressure and surface
tension, and now a non-zero baryon number. The hadron emission from the droplet
is described following Weisskopf's statistical model. We consider evolutions of
droplets with different initial temperatures and net baryon number. It is found
that the introduction of a non-zero net baryon number does not change the
lifetime of the droplets significantly. Only when we consider an initially very
baryon-rich, low-temperature droplets is the lifetime is decreased
significantly. We have, furthermore, found a convergence of both baryon
chemical potential and temperature toward the values 450
MeV and MeV. This convergence is linked to the competing
emission of baryons versus mesons.Comment: 15 pages, 5 figure
Similarities of gauge and gravity amplitudes
We review recent progress in computations of amplitudes in gauge theory and
gravity. We compare the perturbative expansion of amplitudes in N=4 super
Yang-Mills and N=8 supergravity and discuss surprising similarities.Comment: Talk presented by Harald Ita at "Continuous Advances in QCD 2006", 7
page
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
Perturbative Gravity and Twistor Space
The recent progress in computing gauge theory amplitudes can be extended, in
many cases, to theories incorporating gravity. This has improved our
understanding of the perturbative expansion of N=8 supergravity supporting the
``no-triangle hypothesis'' that N=8 one-loop amplitudes may be expressed in
terms of scalar box integral functions.Comment: Talk presented by N. E. J. Bjerrum-Bohr at Loop and Legs 2006, 5
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