Twisted Gravitational Waves in the Presence of a Cosmological Constant
  We find exact nonlinear solutions of general relativity that represent
twisted gravitational waves (TGWs) in the presence of a cosmological constant.
A TGW is a nonplanar wave propagating along a fixed spatial direction with a
null Killing wave vector that has a nonzero twist tensor. The solutions all
turn out to have wave fronts with negative Gaussian curvature. Among the
classes of solutions presented in this paper, we find a unique class of simple
conformally flat TGWs that is due to the presence of a negative cosmological
constant and therefore represents part of anti-de Sitter spacetime. The
properties of this special solution are studied in detail.
