The gravitational index and allowable complex metrics

Abstract: We study the Konstevich--Segal--Witten criterion for allowable complex metrics, in the context of the gravitational path integral corresponding to the supersymmetric index. In various theories of supergravity in asymptotically flat and asymptotically AdS space, the exponential growth of states of the corresponding microscopic index in string theory is known to be captured by complex saddle points of this path integral. We compare the KSW criterion for these complex saddles against constraints from geometric consistency and the convergence of microscopic indices for the same saddles. In all four-dimensional situations we find that the three criteria precisely agree with each other. However, in the AdS$_5$ dual to the superconformal index with unequal chemical potentials for the two angular momenta, we find that this agreement does not hold. The region of convergence of microscopic index in parameter space is a strict subset of the region allowed by the KSW criterion, which in turn is a strict subset of the geometric consistency conditions. We conclude that the KSW criterion is necessary but not sufficient for the allowability of complex metrics contributing to the superconformal index.