A note on classical and quantum unimodular gravity

Abstract

We discuss unimodular gravity at a classical level, and in terms of its extension into the UV through an appropriate path integral representation. Classically, unimodular gravity is simply a gauge fixed version of General Relativity (GR), and as such it yields identical dynamics and physical predictions. We clarify this and explain why there is no sense in which it can "bring a new perspective" to the cosmological constant problem. The quantum equivalence between unimodular gravity and GR is more of a subtle question, but we present an argument that suggests one can always maintain the equivalence up to arbitrarily high momenta. As a corollary to this, we argue that whenever inequivalence is seen at the quantum level, that just means we have defined two different quantum theories that happen to share a classical limit.

5 pages; v2: Some clarifying comments added. Version to appear in European Physical Journal C

References in corpus (2)

• Vacuum Energy Sequestering: The Framework and Its Cosmological Consequences
• On the UV structure of quantum unimodular gravity

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