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Decay Modes of Highly Excited String States and Kerr Black Holes

We consider four-graviton scattering in Type II string theory on one-loop level in the large centre of mass energy M^2 limit. We extract from it an explicit integral expression for the full string theory corrections to the imaginary part of the mass-shift and the lifetime of a massive state with the highest allowed spin J=2M^2+2. We find a decay rate that is up to log M corrections of order 1 in string units, times g_s^2. We also find that the dominant decay mode corresponds to the emission of light particles, whereas the decay into two massive or two massless states is exponentially suppressed. We discuss the relation of our results to quantum gravity aspects of a Kerr Black Hole.