  Chiral gravity is three-dimensional asymptotically AdS3 gravity with an
Einstein, cosmological, and Chern-Simons term at a critical value of the
coupling denoted \mu\ell=1. Ordinarily, excitations of AdS3 gravity are known
to transform non-trivially under an asymptotic symmetry group consisting of
both a left-moving and a right-moving conformal group. However it was recently
conjectured in arXiv:0801.4566 that at the chiral point \mu\ell=1 all
excitations are chiral in that they transform only under the right-moving
conformal group. We show herein that at the chiral point, the group of trivial
diffeomorphisms is enhanced to include the left-moving conformal
transformations, and the asymptotic symmetry group contains only one
(right-moving) copy of the conformal group. Diffeomorphism invariance then
requires that all physical excitations are annihilated by left-moving conformal
transformations, establishing nonperturbatively the chiral nature of chiral
gravity.
