22,911 research outputs found
Graviton Amplitudes from Collinear Limits of Gauge Amplitudes
We express all tree-level graviton amplitudes in Einstein's gravity as the
collinear limits of a linear combination of pure Yang-Mills amplitudes in which
each graviton is represented by two gauge bosons, each of them carrying exactly
one half of graviton's momentum and helicity.Comment: 7 pages, harvma
Graviton as a Pair of Collinear Gauge Bosons
We show that the mixed gravitational/gauge superstring amplitudes describing
decays of massless closed strings - gravitons or dilatons - into a number of
gauge bosons, can be written at the tree (disk) level as linear combinations of
pure open string amplitudes in which the graviton (or dilaton) is replaced by a
pair of collinear gauge bosons. Each of the constituent gauge bosons carry
exactly one half of the original closed string momentum, while their +/- 1
helicities add up to +/- 2 for the graviton or to 0 for the dilaton.Comment: 10 pages, harvmac; v2: references adde
Subleading Terms in the Collinear Limit of Yang-Mills Amplitudes
For two massless particles i and j, the collinear limit is a special
kinematic configuration in which the particles propagate with parallel
four-momentum vectors, with the total momentum P distributed as p_i=xP and
p_j=(1-x)P, so that s_{ij}=(p_i+p_j)^2=P^2=0. In Yang-Mills theory, if i and j
are among N gauge bosons participating in a scattering process, it is well
known that the partial amplitudes associated to the (single trace) group
factors with adjacent i and j are singular in the collinear limit and factorize
at the leading order into N-1-particle amplitudes times the universal,
x-dependent Altarelli-Parisi factors. We give a precise definition of the
collinear limit and show that at the tree level, the subleading, non-singular
terms are related to the amplitudes with a single graviton inserted instead of
two collinear gauge bosons. To that end, we argue that in one-graviton
Einstein-Yang-Mills amplitudes, the graviton with momentum P can be replaced by
a pair of collinear gauge bosons carrying arbitrary momentum fractions xP and
(1-x)P.Comment: 8 page
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