Arguments Against a Finite N=8 Supergravity
  I present arguments based on dispersion theory and the existence of charged BPS states of small charge, that maximally supersymmetric SUGRA is not a finite theory. The essence of the argument is that the perturbative construction of the theory implies that scattering amplitudes are invariant under a continuous SU(8) global symmetry, which is broken by contributions from virtual BPS states. Conventional estimates of the contributions of those states above production threshold, shows that they should be order one. If the amplitude satisfies a dispersion relation with a finite number of subtractions, as has recently been argued by Giddings and Porto [1], then SU(8) violating amplitudes appear at finite orders in the low energy expansion. We also make a brief remark about the inconsistency of the idea of classicalization in non-gravitational theories. 
T. Banks
hep-th gr-qc