Abstract :

I consider the spacetimes describing pp-waves propagating on extremal non-dilatonic branes. It is shown that an observer moving along a geodesic will experience infinite curvature at the horizon of the brane, which should therefore be regarded as singular. There are thus naked singularities in the Randall-Sundrum scenario. Taking the decoupling limit of these brane-wave spacetimes gives a pp-wave in AdS, the simplest example being the Kaigorodov spacetime. It has been conjectured that gravity in this spacetime is dual to a CFT in the infinite momentum frame with constant momentum density. If correct, this implies that the CFT must resolve the singularity of the bulk spacetime. Evidence in favour of this conjecture is presented. The unbroken conformal symmetries determine the scalar 2-point function up to an arbitrary function of one variable. However, an AdS/CFT calculation shows that this function is constant (to leading order in 1/N^2) and the result is therefore the same as when the full conformal symmetry is unbroken. I conclude by pointing out possible connections with the DLCQ description of "little string theories", in particular with that of the (2,0) matrix model of M5-branes.

References : hep-th/0012076