Scattering amplitudes for cylindrical gravitational waves

Cylindrical gravitational waves are interesting because they enjoy an infinite dimensional symmetry called Geroch symmetry. In this paper, we compute the 2-particle tree-level S-matrix for cylindrical gravitational waves. The model we use is a dimensional reduction of general relativity to two spacetime dimensions. The reduced theory is a nonlinear sigma model. We discuss an SO(2) symmetry of the amplitudes which is a special case of Geroch symmetry.
Comment: 8 pages, 1 figures