%0 Journal Article
%T Spacelike Singularities and Hidden Symmetries of Gravity
%A Henneaux Marc
%A Persson Daniel
%A Spindel Philippe
%J Living Reviews in Relativity
%D 2008
%I Max-Planck Institute for Gravitational Physics
%X We review the intimate connection between (super-)gravity close to a spacelike singularity (the ˇ°BKL-limitˇ±) and the theory of Lorentzian Kac-Moody algebras. We show that in this limit the gravitational theory can be reformulated in terms of billiard motion in a region of hyperbolic space, revealing that the dynamics is completely determined by a (possibly infinite) sequence of reflections, which are elements of a Lorentzian Coxeter group. Such Coxeter groups are the Weyl groups of infinite-dimensional Kac-Moody algebras, suggesting that these algebras yield symmetries of gravitational theories. Our presentation is aimed to be a self-contained and comprehensive treatment of the subject, with all the relevant mathematical background material introduced and explained in detail. We also review attempts at making the infinite-dimensional symmetries manifest, through the construction of a geodesic sigma model based on a Lorentzian Kac-Moody algebra. An explicit example is provided for the case of the hyperbolic algebra E_10, which is conjectured to be an underlying symmetry of M-theory. Illustrations of this conjecture are also discussed in the context of cosmological solutions to eleven-dimensional supergravity.
%K hidden symmetries
%K duality
%K Kac-Moody algebras
%U http://www.livingreviews.org/lrr-2008-1