Kaigorodov spaces and their Penrose limits

Kaigorodov spaces arise, after spherical compactification, as near-horizon limits of M2, M5 and D3-branes with a particular pp-wave propagating in a worldvolume direction. We show that the uncompactified near-horizon configurations K × S are solutions of D = 11 or D = 10 IIB supergravity which correspond to perturbed versions of their AdS × S analogues. We derive the Penrose–Güven limits of the Kaigorodov space and the total spaces and analyse their symmetries. An Inönü–Wigner contraction of the Lie algebra is shown to occur, although there is a symmetry enhancement. We compare the results to the maximally supersymmetric CW spaces found as limits of AdS × S spacetimes: the initial gravitational perturbation on the brane and its near-horizon geometry remains after taking non-trivial Penrose limits, but seems to decouple. One particular limit yields a time-dependent homogeneous plane-wave background whose string theory is solvable, while in the other cases we find inhomogeneous backgrounds.