336 research outputs found
Predicting a Prior for Planck
The quantum state of the universe combined with the structure of the
landscape potential implies a prior that specifies predictions for
observations. We compute the prior for CMB related observables given by the
no-boundary wave function (NBWF) in a landscape model that includes a range of
inflationary patches representative of relatively simple single-field models.
In this landscape the NBWF predicts our classical cosmological background
emerges from a region of eternal inflation associated with a plateau-like
potential. The spectra of primordial fluctuations on observable scales are
characteristic of concave potentials, in excellent agreement with the Planck
data. By contrast, alternative theories of initial conditions that strongly
favor inflation at high values of the potential are disfavored by observations
in this landscape.Comment: 18 pages, 5 figures; v2: minor corrections/clarifications; v3:
published version, more explanation on top-down probability distribution over
background
An AdS Crunch in Supergravity
We review some properties of N=8 gauged supergravity in four dimensions with
modified, but AdS invariant boundary conditions on the m^2=-2 scalars. There is
a one-parameter class of asymptotic conditions on these fields and the metric
components, for which the full AdS symmetry group is preserved. The generators
of the asymptotic symmetries are finite, but acquire a contribution from the
scalar fields. For a large class of such boundary conditions, we find there
exist black holes with scalar hair that are specified by a single conserved
charge. Since Schwarschild-AdS is a solution too for all boundary conditions,
this provides an example of black hole non-uniqueness. We also show there exist
solutions where smooth initial data evolve to a big crunch singularity. This
opens up the possibility of using the dual conformal field theory to obtain a
fully quantum description of the cosmological singularity, and we report on a
preliminary study of this.Comment: 25 pages, to appear in the proceedings of the conference on Strings
and Cosmology, Texas A&M University, March 200
Replication Regulates Volume Weighting in Quantum Cosmology
Probabilities for observations in cosmology are conditioned both on the
universe's quantum state and on local data specifying the observational
situation. We show the quantum state defines a measure for prediction through
such conditional probabilities that is well behaved for spatially large or
infinite universes when the probabilities that our data is replicated are taken
into account. In histories where our data are rare volume weighting connects
top-down probabilities conditioned on both the data and the quantum state to
the bottom-up probabilities conditioned on the quantum state alone. We apply
these principles to a calculation of the number of inflationary e-folds in a
homogeneous, isotropic minisuperspace model with a single scalar field moving
in a quadratic potential. We find that volume weighting is justified and the
top-down probabilities favor a large number of e-folds.Comment: 13 pages, 3 figures; v2: correction case of data on multiple
surfaces, clarification objectivit
Quantum Transitions Between Classical Histories: Bouncing Cosmologies
In a quantum theory of gravity spacetime behaves classically when quantum
probabilities are high for histories of geometry and field that are correlated
in time by the Einstein equation. Probabilities follow from the quantum state.
This quantum perspective on classicality has important implications: (a)
Classical histories are generally available only in limited patches of the
configuration space on which the state lives. (b) In a given patch states
generally predict relative probabilities for an ensemble of possible classical
histories. (c) In between patches classical predictability breaks down and is
replaced by quantum evolution connecting classical histories in different
patches. (d) Classical predictability can break down on scales well below the
Planck scale, and with no breakdown in the classical equations of motion. We
support and illustrate (a)-(d) by calculating the quantum transition across the
de Sitter like throat connecting asymptotically classical, inflating histories
in the no-boundary quantum state. This supplies probabilities for how a
classical history on one side transitions and branches into a range of
classical histories on the opposite side. We also comment on the implications
of (a)-(d) for the dynamics of black holes and eternal inflation.Comment: 37 pages, 5 figures, minor corrections, results not change
Axion Wormholes in AdS Compactifications
We find regular axionic Euclidean wormhole solutions in Type IIB string
theory compactified on . AdS/CFT
enables a precise derivation of the axion content of the Euclidean theory,
placing the string theory embedding of the wormholes on firm footing. This
further sharpens the paradox posed by these solutions.Comment: 11 page
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