A black hole instability in five dimensions?

We study the moduli-space scattering of a two-charge supertube in thebackground of a rotating BPS D1-D5-P black hole in 4+1 dimensions, extendingthe static analysis of Bena and Kraus (hep-th/0402144). While the magneticforces associated with this motion change the details considerably, the finalconclusion is similar to that of the static analysis: we find that one canbring the supertube to the horizon, so that the BMPV black hole and thesupertube merge. However, our analysis shows that this can occur even atsignificantly larger values of the angular momentum than was indicated by thestatic analysis. For a range of parameters, conservation laws and the areatheorem forbid the result of the merger from being any single known object:neither near-extremal black holes nor non-supersymmetric black rings areallowed. Such results suggest that the merger triggers an instability of therotating D1-D5-P black hole, perhaps leading to bifurcation into a pair ofblack objects.Comment: 25 pages, 4 figures; v2: references adde