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arXiv · 1509.00851

Quantum Gravity Constraints from Unitarity and Analyticity

Brando Bellazzini·Clifford Cheung·Grant N. Remmen
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Abstract

We derive rigorous bounds on corrections to Einstein gravity using unitarity and analyticity of graviton scattering amplitudes. In $D\geq 4$ 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 $D\geq 6$. 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 $D\geq 5$ 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.

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Brando Bellazzini, Clifford Cheung, Grant N. Remmen. 2015-09-02. Quantum Gravity Constraints from Unitarity and Analyticity. https://doi.org/10.1103/physrevd.93.064076

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