How unimodular gravity theories differ from general relativity at quantum level

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Bufalo , R , Oksanen , M & Tureanu , A 2015 , ' How unimodular gravity theories differ from general relativity at quantum level ' , European Physical Journal C. Particles and Fields , vol. 75 , no. 10 , 477 . https://doi.org/10.1140/epjc/s10052-015-3683-3

Title: How unimodular gravity theories differ from general relativity at quantum level
Author: Bufalo, R.; Oksanen, M.; Tureanu, A.
Contributor: University of Helsinki, Department of Physics
University of Helsinki, Department of Physics
Date: 2015-10-06
Language: eng
Number of pages: 20
Belongs to series: European Physical Journal C. Particles and Fields
ISSN: 1434-6044
URI: http://hdl.handle.net/10138/174050
Abstract: We investigate path integral quantization of two versions of unimodular gravity. First a fully diffeomorphism-invariant theory is analyzed, which does not include a unimodular condition on the metric, while still being equivalent to other unimodular gravity theories at the classical level. The path integral has the same form as in general relativity (GR), except that the cosmological constant is an unspecified value of a variable, and it thus is unrelated to any coupling constant. When the state of the universe is a superposition of vacuum states, the path integral is extended to include an integral over the cosmological constant. Second, we analyze the standard unimodular theory of gravity, where the metric determinant is fixed by a constraint. Its path integral differs from the one of GR in two ways: the metric of spacetime satisfies the unimodular condition only in average over space, and both the Hamiltonian constraint and the associated gauge condition have zero average over space. Finally, the canonical relation between the given unimodular theories of gravity is established.
Subject: COSMOLOGICAL-CONSTANT PROBLEM
TIME
114 Physical sciences
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