Observations on arithmetic invariants and U-duality orbits in N = 8 supergravity

We establish a relation between time-like, light-like and space-like orbits of the non-compact E-7(7)(R) symmetry and discrete E-7(7)(Z) invariants. We discuss the U-duality invariant formula for the degeneracy of states d(Q) which in the approximation of large occupation numbers reproduces the Bekenstein-Hawking entropy formula for regular black holes with AdS(2) horizon. We explain why the states belonging to light-like orbits, corresponding to classical solutions of "light black holes with null singularity", decouple from the corresponding index. We also present a separate U-duality invariant formula for the class of light-like orbits specified by discrete E-7(7)(Z) invariants. We conclude that the present study of the non-perturbative sector of the theory does not reveal any contradiction with the conjectured all-loop perturbative finiteness of D = 4 N = 8 supergravity.