35 research outputs found
Maximally Helicity Violating Disk Amplitudes, Twistors and Transcendental Integrals
We obtain simple expressions for tree-level maximally helicity violating
amplitudes of N gauge bosons from disk world-sheets of open superstrings. The
amplitudes are written in terms of (N-3)! hypergeometric integrals depending on
kinematic parameters, weighted by certain kinematic factors. The integrals are
transcendental in a strict sense defined in this work. The respective kinematic
factors can be succinctly written in terms of "dual" momentum twistors. The
amplitudes are computed by using the prescription proposed by Berkovits and
Maldacena.Comment: 7 page
Disk level S-matrix elements at eikonal Regge limit
We examine the calculation of the color-ordered disk level S-matrix element
of massless scalar vertex operators for the special case that some of the
Mandelstam variables for which there are no open string channel in the
amplitude, are set to zero. By explicit calculation we show that the string
form factors in the 2n-point functions reduce to one at the eikonal Regge
limit.Comment: 17 pages, Latex file, no figur
Supersymmetry Relations and MHV Amplitudes in Superstring Theory
We discuss supersymmetric Ward identities relating various scattering
amplitudes in type I open superstring theory. We show that at the disk level,
the form of such relations remains exactly the same, to all orders in alpha',
as in the low-energy effective field theory describing the alpha'-> 0 limit.
This result holds in D=4 for all compactifications, even for those that break
supersymmetry. We apply SUSY relations to the computations of N-gluon MHV
superstring amplitudes, simplifying the existing results for N<7 and deriving a
compact expression for N=7.Comment: 34 pages, harvmac; v2: 2 figs added; final version to appear in NP
Higher Spin Scattering in Superstring Theory
We compute scattering amplitudes of leading Regge trajectory states in open
superstring theories. Highest spin states at mass level n with spin s=n+1 for
bosons and s=n+1/2 for fermions are generated by particularly simple vertex
operators. Hence, the cubic couplings of bosons and fermions on the leading
Regge trajectory are given for arbitrary n. The same can be achieved for higher
point amplitudes, and this article focuses on four point level with one heavy
maximum spin state and three massless states in any bose-fermi combination,
putting particular emphasis on manifest cyclic symmetry. Except for the four
fermion coupling, all our results remain valid in any D<10 dimensional
compactification scenario, so they might become relevant at LHC in case of an
experimentally accessible low string scale. But even if not directly
observable, superstring amplitudes provide important clues on higher spin
dynamics and their consistent interactions in field theory.Comment: 31 pages; v3: final version published in Nuclear Physics