A simple approach to counterterms in N=8 supergravity

We present a simple systematic method to study candidate counterterms in N = 8 supergravity. Complicated details of the counterterm operators are avoided because we work with the on-shell matrix elements they produce. All n-point matrix elements of an independent SUSY invariant operator of the form DR + . . . must be local and satisfy SUSY Ward identities. These are strong constraints, and we test directly whether or not matrix elements with these properties can be constructed. If not, then the operator does not have a supersymmetrization, and it is excluded as a potential counterterm. For n > 4, we find that R, DR, DR, and DR are excluded as counterterms of MHV amplitudes, while only R and DR are excluded at the NMHV level. As a consequence, for loop order L < 7, there are no independent DR counterterms with n > 4. If an operator is not ruled out, our method constructs an explicit superamplitude for its matrix elements. This is done for the 7-loop DR operator at the NMHV level and in other cases. We also initiate the study of counterterms without leading pure-graviton matrix elements, which can occur beyond the MHV level. The landscape of excluded/allowed candidate counterterms is summarized in a colorful chart. ar X iv :1 00 3. 50 18 v2 [ he pth ] 2 8 O ct 2 01 0