Scattering amplitudes in strongly coupled N=4 SYM from semiclassical strings in AdS

TL;DR

This paper explores how scattering amplitudes in strongly coupled N=4 SYM can be computed using semiclassical string solutions in AdS, revealing a universal exponential factor and suggesting a simplification of amplitudes at strong coupling.

Contribution

It proposes that at strong coupling, all scattering amplitudes in N=4 SYM are given by tree-level Yang-Mills amplitudes multiplied by a universal exponential factor, extending previous MHV-specific results.

Findings

Amplitudes at strong coupling are helicity and particle-type independent.

The prefactor of string amplitudes matches tree-level Yang-Mills amplitudes.

Strong coupling amplitudes simplify to a universal exponential times tree-level results.

Abstract

Very recently in arXiv:0705.0303 Alday and Maldacena gave a string theory prescription for computing (all) planar amplitudes in N=4 supersymmetric gauge theory at strong coupling using the AdS/CFT correspondence. These amplitudes are determined by a classical string solution and contain a universal exponential factor involving the action of the classical string. On the gauge theory side, expressions for perturbative amplitudes at strong coupling were previously proposed only for specific helicities of external particles -- the maximally helicity violating or MHV amplitudes. These follow from the exponential ansatz of Bern, Dixon and Smirnov for MHV amplitudes in N=4 SYM. In this paper we examine the amplitudes dependence on helicities and particle-types of external states. We consider the prefactor of string amplitudes and give arguments suggesting that the prefactor at strong coupling should be the same as the Yang-Mills tree-level amplitude for the same process. This implies that scattering amplitudes in N=4 SYM simplify dramatically in the strong coupling limit. It follows from our proposal that in this limit all (MHV and non-MHV) n-point amplitudes are given by the (known) tree-level Yang-Mills result times the helicity-independent (and particle-type-independent) universal exponential.