Unimodular loop quantum cosmology

Journal Article · Wed Sep 15 00:00:00 EDT 2010 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.82.064012· OSTI ID:21421154

Chiou, D -W; Geiller, Marc ^[1]

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1. Department of Physics, Beijing Normal University, Beijing 100875 (China)

Unimodular gravity is based on a modification of the usual Einstein-Hilbert action that allows one to recover general relativity with a dynamical cosmological constant. It also has the interesting property of providing, as the momentum conjugate to the cosmological constant, an emergent clock variable. In this paper we investigate the cosmological reduction of unimodular gravity, and its quantization within the framework of flat homogeneous and isotropic loop quantum cosmology. It is shown that the unimodular clock can be used to construct the physical state space, and that the fundamental features of the previous models featuring scalar field clocks are reproduced. In particular, the classical singularity is replaced by a quantum bounce, which takes place in the same condition as obtained previously. We also find that requirement of semiclassicality demands the expectation value of the cosmological constant to be small (in Planck units). The relation to spin foam models is also studied, and we show that the use of the unimodular time variable leads to a unique vertex expansion.

• OSTI ID: 21421154
• Journal Information: Physical Review. D, Particles Fields, Vol. 82, Issue 6; Other Information: DOI: 10.1103/PhysRevD.82.064012; (c) 2010 American Institute of Physics; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COSMOLOGICAL CONSTANT
COSMOLOGY
EXPANSION
EXPECTATION VALUE
GENERAL RELATIVITY THEORY
GRAVITATION
MODIFICATIONS
QUANTIZATION
SCALAR FIELDS
SINGULARITY
SPIN
ANGULAR MOMENTUM
FIELD THEORIES
PARTICLE PROPERTIES
RELATIVITY THEORY