Covariant BRST Quantization of Unimodular Gravity I -- Formulation with antisymmetric tensor ghosts --

Abstract

Unimodular gravity (UG) is an interesting theory that may explain why the cosmological constant is extremely small, in contrast to general relativity (GR). The theory has only the transverse diffeomorphism invariance and this causes lots of debate as to the equivalence of UG to GR in the covariant quantization. We study the covariant BRST quantization of UG by gauge fixing only the transverse diffeomorphism and show that the remaining physical degrees of freedom are two, the same number as GR. This is achieved by using antisymmetric tensor ghost fields which automatically satisfy the transverse condition without nonlocal projection operator. The theory exhibits the ghosts for ghosts phenomenon, which requires further gauge fixing and introduction of more ghosts. We identify the BRST quartet structure among the various fields and single out the remaining physical degrees of freedom.

arXiv comment35 pages, v2: a footnote added, minor corrections

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• Unimodular Gravity vs General Relativity: A status report
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• Gauge symmetry of unimodular gravity in Hamiltonian formalism
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• Unimodular gravity and the gauge/gravity duality
• Gauge invariant renormalizability of quantum gravity
• Thermodynamics as a tool for (quantum) gravitational dynamics
• The quantum dynamics of Lagrange multipliers
• Unimodular Plebański Gravity
• Covariant BRST Quantization of Unimodular Gravity II -- Formulation with a vector antighost --