Path-integral measures determine operator orderings for the Wheeler-DeWitt equation in flat minisuperspace models, with all consistent choices yielding identical physical observables via field redefinition Jacobians.
The Classical Universes of the No-Boundary Quantum State
3 Pith papers cite this work. Polarity classification is still indexing.
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abstract
We analyze the origin of the quasiclassical realm from the no-boundary proposal for the universe's quantum state in a class of minisuperspace models. The models assume homogeneous, isotropic, closed spacetime geometries, a single scalar field moving in a quadratic potential, and a fundamental cosmological constant. The allowed classical histories and their probabilities are calculated to leading semiclassical order. We find that for the most realistic range of parameters analyzed a minimum amount of scalar field is required, if there is any at all, in order for the universe to behave classically at late times. If the classical late time histories are extended back, they may be singular or bounce at a finite radius. The ensemble of classical histories is time symmetric although individual histories are generally not. The no-boundary proposal selects inflationary histories, but the measure on the classical solutions it provides is heavily biased towards small amounts of inflation. However, the probability for a large number of efoldings is enhanced by the volume factor needed to obtain the probability for what we observe in our past light cone, given our present age. Our results emphasize that it is the quantum state of the universe that determines whether or not it exhibits a quasiclassical realm and what histories are possible or probable within that realm.
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Switching to 3-torus topology and summing SL(3,Z) geometries via automorphic forms makes the no-boundary wavefunction favor large inflating universes with over 250 e-folds, plus CMB corrections from torus moduli.
Disk path integrals of timelike Liouville theory yield one-loop Hartle-Hawking-like wavefunctions in a fixed extrinsic-curvature representation, with a conjectured all-loop form and a K-independent pairing that may define a cosmological inner product.
citing papers explorer
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Ordering-Independent Wheeler-DeWitt Equation for Flat Minisuperspace Models
Path-integral measures determine operator orderings for the Wheeler-DeWitt equation in flat minisuperspace models, with all consistent choices yielding identical physical observables via field redefinition Jacobians.
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Inflation and topology from the no-boundary state
Switching to 3-torus topology and summing SL(3,Z) geometries via automorphic forms makes the no-boundary wavefunction favor large inflating universes with over 250 e-folds, plus CMB corrections from torus moduli.
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Quantum Liouville Cosmology
Disk path integrals of timelike Liouville theory yield one-loop Hartle-Hawking-like wavefunctions in a fixed extrinsic-curvature representation, with a conjectured all-loop form and a K-independent pairing that may define a cosmological inner product.