1,442 research outputs found
Gravitational Mediation of Supersymmetry Breaking in Superstring Theory
SUSY breaking and its mediation are among the most important problems of
supersymmetric generalizations of the standard model. The idea of
gravity-mediated SUSY breaking, proposed in 1982 by Arnowitt, Chamseddine and
Nath, and independently by Barbieri, Ferrara and Savoy, fits naturally into
superstring theory, where it can be realized at both classical as well as
quantum levels. This talk is dedicated to Pran Nath on his 65th birthday.Comment: 8 pages. Dedicated to Pran Nath on his 65th birthda
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
Closed String Amplitudes as Single-Valued Open String Amplitudes
We show that the single trace heterotic N-point tree-level gauge amplitude
A_HET can be obtained from the corresponding type I amplitude A_I by the
single-valued (sv) projection: A_HET=sv(A_I). This projection maps multiple
zeta values to single-valued multiple zeta values. The latter represent a
subclass of multiple zeta values originating from single-valued multiple
polylogarithms at unity. Similar relations between open and closed string
amplitudes or amplitudes of different string vacua can be established. As a
consequence the alpha'-expansion of a closed string amplitude is dictated by
that of the corresponding open string amplitude. The combination of
single-valued projections, Kawai-Lewellen-Tye relations and Mellin
correspondence reveal a unity of all tree-level open and closed superstring
amplitudes together with the maximally supersymmetric Yang-Mills and
supergravity theories.Comment: 25 pages, harvma
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