2015/09/30 by Brando Bellazzini, Clifford Cheung, Grant N. Remmen · 2 citations
Physics and Astronomy · #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevd.93.064076
published as Phys. Rev. D 93, 064076 (2016) · 26 pages
arxiv created 2016/03/31 · arxiv updated 2016/04/06
We derive rigorous bounds on corrections to Einstein gravity using unitarity and analyticity of graviton scattering amplitudes. In D≥ 4 spacetime dimensions, these consistency conditions mandate positive coefficients for certain quartic curvature operators. We systematically enumerate all such positivity bounds in D=4 and D=5 before extending to D≥ 6. Afterwards, we derive positivity bounds for supersymmetric operators and verify that all of our constraints are satisfied by weakly-coupled string theories. Among quadratic curvature operators, we find that the Gauss-Bonnet term in D≥ 5 is inconsistent unless new degrees of freedom enter at the natural cutoff scale defined by the effective theory. Our bounds apply to perturbative ultraviolet completions of gravity.