Simplifying Quantum Gravity Calculations

TL;DR

This paper develops a method to simplify Feynman rules in quantum gravity by using a generalized gauge and field redefinitions, making calculations more manageable while maintaining accuracy.

Contribution

It introduces a parameterized approach to simplify gravity Feynman rules, especially for graviton vertices, and verifies the simplifications through amplitude calculations.

Findings

Simplified Feynman rules for gravity vertices.

Validated simplifications with tree-level amplitude calculations.

Demonstrated utility in one-loop scalar-graviton scattering diagrams.

Abstract

The Einstein-Hilbert Lagrangian for gravity is non-renormalizable at loop level. However, it can be treated in the effective field theory framework which means that gravity as an effective theory can be renormalized when a proper expansion of the effective Lagrangian is made. At the same time, the Feynman rules for gravity are very complicated, although the resulting amplitudes do not have the same complications. Therefore, in this thesis we want to simplify the Feynman rules as much as possible by using the most general parameterized gauge condition, adding all possible parameterized total derivative terms and redefining the gravitational, ghosts and scalar fields in a general parameterization way. By choosing the parameters in a specific way, we obtain simplified Feynman rules, especially the triple and quadruple graviton vertices are simplified. In addition, we verify our simplified rules by calculating the amplitudes of scalar-graviton and graviton-graviton scattering at tree level using the simplified and standard Feynman rules. Finally, we show the utility of these simplified rules by calculating some one-loop diagrams for scalar-graviton scattering and comparing to the standard Feynman rules.