Gravitational Effective Field Theory Islands, Low-Spin Dominance, and the Four-Graviton Amplitude

Understand

We analyze constraints from perturbative unitarity and crossing on the leading contributions of higher-dimension operators to the four-graviton amplitude in four spacetime dimensions, including constraints that follow from distinct helicity configurations.

• We focus on the leading-order effect due to exchange by massive degrees of freedom which makes the amplitudes of interest infrared finite.
• In particular, we place a bound on the coefficient of the $R^3$ operator that corrects the graviton three-point amplitude in terms of the $R^4$ coefficient.
• To test the constraints we obtain nontrivial effective field-theory data by computing and taking the large-mass expansion of the one-loop minimally-coupled four-graviton amplitude with massive particles up to spin 2 circulating in the loop.