title: Cancellations beyond finiteness in N=8 supergravity at three loops.
abstract: We construct the three-loop four-point amplitude of N=8 supergravity using the unitarity method. The amplitude is ultraviolet finite in four dimensions. Novel cancellations, not predicted by traditional superspace power-counting arguments, render its degree of divergence in D dimensions no worse than that of N=4 super-Yang-Mills theory--a finite theory in four dimensions. Similar cancellations can be identified at all loop orders in certain unitarity cuts, suggesting that N=8 supergravity may be a perturbatively finite theory of quantum gravity.
authors.affiliation: Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1547, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Bern
authors.forename: J J
authors.initials: JJ
authors.lastname: Carrasco
authors.forename: L J
authors.initials: LJ
authors.lastname: Dixon
authors.forename: H
authors.initials: H
authors.lastname: Johansson
authors.forename: D A
authors.initials: DA
authors.lastname: Kosower
authors.forename: R
authors.initials: R
authors.lastname: Roiban