Background independence in a background dependent renormalization group

Understand

Within the derivative expansion of conformally reduced gravity, the modified split Ward identities are shown to be compatible with the flow equations if and only if either the anomalous dimension vanishes or the cutoff profile is chosen to be power law.

• No solutions exist if the Ward identities are incompatible.
• In the compatible case, a clear reason is found for why Ward identities can still forbid the existence of fixed points; however, for any cutoff profile, a background independent (and parametrisation independent) flow equation is uncovered.
• Finally, expanding in vertices, the combined equations are shown generically to become either over-constrained or highly redundant beyond the six-point level.