5,903 research outputs found
Decoherence of Histories and Hydrodynamic Equations for a Linear Oscillator Chain
We investigate the decoherence of histories of local densities for linear
oscillators models. It is shown that histories of local number, momentum and
energy density are approximately decoherent, when coarse-grained over
sufficiently large volumes. Decoherence arises directly from the proximity of
these variables to exactly conserved quantities (which are exactly decoherent),
and not from environmentally-induced decoherence. We discuss the approach to
local equilibrium and the subsequent emergence of hydrodynamic equations for
the local densities.Comment: 37 pages, RevTe
A proper-time cure for the conformal sickness in quantum gravity
Starting from the space of Lorentzian metrics, we examine the full
gravitational path integral in 3 and 4 space-time dimensions. Inspired by
recent results obtained in a regularized, dynamically triangulated formulation
of Lorentzian gravity, we gauge-fix to proper-time coordinates and perform a
non-perturbative ``Wick rotation'' on the physical configuration space. Under
certain assumptions about the behaviour of the partition function under
renormalization, we find that the divergence due to the conformal modes of the
metric is cancelled non-perturbatively by a Faddeev-Popov determinant
contributing to the effective measure. We illustrate some of our claims by a 3d
perturbative calculation.Comment: 25 pages, 1 postscript figure; version to appear in Nucl. Phys. B
with an added reference and a commen
Approximate Decoherence of Histories and 't Hooft's Deterministic Quantum Theory
This paper explores the possibility that an exactly decoherent set of
histories may be constructed from an approximately decoherent set by small
distortions of the operators characterizing the histories. In particular, for
the case of histories of positions and momenta, this is achieved by doubling
the set of operators and then finding, amongst this enlarged set, new position
and momentum operators which commute, so decohere exactly, and which are
``close'' to the original operators. The enlarged, exactly decoherent, theory
has the same classical dynamics as the original one, and coincides with the
so-called deterministic quantum theories of the type recently studied by 't
Hooft. These results suggest that the comparison of standard and deterministic
quantum theories may provide an alternative method of characterizing emergent
classicality. A side-product is the surprising result that histories of momenta
in the quantum Brownian motion model (for the free particle in the
high-temperature limit) are exactly decoherent.Comment: 41 pages, plain Te
Quantum measure and integration theory
This article begins with a review of quantum measure spaces. Quantum forms
and indefinite inner-product spaces are then discussed. The main part of the
paper introduces a quantum integral and derives some of its properties. The
quantum integral's form for simple functions is characterized and it is shown
that the quantum integral generalizes the Lebesgue integral. A bounded,
monotone convergence theorem for quantum integrals is obtained and it is shown
that a Radon-Nikodym type theorem does not hold for quantum measures. As an
example, a quantum-Lebesgue integral on the real line is considered.Comment: 28 page
Commuting Position and Momentum Operators, Exact Decoherence and Emergent Classicality
Inspired by an old idea of von Neumann, we seek a pair of commuting operators
X,P which are, in a specific sense, "close" to the canonical non-commuting
position and momentum operators, x,p. The construction of such operators is
related to the problem of finding complete sets of orthonormal phase space
localized states, a problem severely constrained by the Balian-Low theorem.
Here these constraints are avoided by restricting attention to situations in
which the density matrix is reasonably decohered (i.e., spread out in phase
space). Commuting position and momentum operators are argued to be of use in
discussions of emergent classicality from quantum mechanics. In particular,
they may be used to give a discussion of the relationship between exact and
approximate decoherence in the decoherent histories approach to quantum theory.Comment: 28 pages, RevTe
Time dependent Green functions from Wheeler De Witt solutions
The aim of this article is twofold. First we examine from a new angle the
question of recovery of time in quantum cosmology. We construct Green functions
for matter fields from the solutions of the Wheeler De Witt equation. For
simplicity we work in a mini-superspace context. By evaluating these Green
functions in a first order development of the energy ``increment'' induced by
matrix elements of field operators, we show that the background geometry is the
solution of Einstein equations driven by the mean matter energy and that it is
this background which determines the time lapses separating the field
operators. Then, by studying higher order corrections, we clarify the nature of
the small dimensionless parameters which guarantee the validity of the
approximations used. In this respect, we show that the formal expansion in the
inverse Planck mass which is sometime presented as the ``standard procedure''
is illegitimate. Secondly, by the present analysis of Green functions, we
prepare the study of quantum matter transitions in quantum cosmology. In a next
article, we show that the time parametrization of transition amplitudes appears
for the same reasons that it appeared in this article. This proves that the
background is dynamically determined by the transition under examination.Comment: 25 pages, latex, no figure
The exact cosmological solution to the dynamical equations for the Bianchi IX model
Quantum geometrodynamics in extended phase space describes phenomenologically
the integrated system ``a physical object + observation means (a gravitational
vacuum condensate)''. The central place in this version of QGD belongs to the
Schrodinger equation for a wave function of the Universe. An exact solution to
the ``conditionally-classical'' set of equations in extended phase space for
the Bianchi-IX model and the appropriate solution to the Schrodinger equation
are considered. The physical adequacy of the obtained solutions to existing
concepts about possible cosmological scenarios is demonstrated. The
gravitational vacuum condensate is shown to be a cosmological evolution factor.Comment: LaTeX, 14 pages, to be published in Int. J. Mod. Phys.
The Isaacson expansion in quantum cosmology
This paper is an application of the ideas of the Born-Oppenheimer (or
slow/fast) approximation in molecular physics and of the Isaacson (or
short-wave) approximation in classical gravity to the canonical quantization of
a perturbed minisuperspace model of the kind examined by Halliwell and Hawking.
Its aim is the clarification of the role of the semiclassical approximation and
the backreaction in such a model. Approximate solutions of the quantum model
are constructed which are not semiclassical, and semiclassical solutions in
which the quantum perturbations are highly excited.Comment: Revtex, 11 journal or 24 preprint pages. REPLACEMENT: A comment on
previous work by Dowker and Laflamme is corrected. Utah preprint
UU-REL-93/3/1
Dis/embodied leadership : intersections of leadership and social class
One weakness with the discursive leadership to date is the failure to explore ways in which material conditions also shape leadership (Fairhurst, 2009). Further, Dougherty (2011) argued that discursive constructionism without a consideration of material conditions is middle class privilege. By privileging the discursive over the material, discursive leadership could be reproducing social inequalities, which relates to issues of social class. The purpose of this dissertation is to understand how leadership and social class become mutually constructed through the interplay between discourse and materiality. The concepts of text work and body work are used to understand how social class is linked with the types of work an individual does. Similar to white-collar/blue-collar distinctions, text work refers to jobs that emphasize the use of communication, and body work refers to jobs that emphasize more physical labor (Dougherty, 2011). A thematic narrative analysis was applied to stories about leadership that were told during interviews with a total of 21 participants (10 body workers and 11 text workers), and observations added context and thick description to participants' narratives about leadership. The theory of Language Convergence/Meaning Divergence provided a lens for understanding how meanings for leadership diverge based on different material experiences in day-to-day work. Findings indicate that discursive and material conditions of work interact to construct different meanings for leadership. Text workers emphasized communication in their constructions of leadership, while body workers constructed leadership more as an embodied practice. Additionally, compared to text workers, body workers demonstrated a more nuanced understanding of leadership that integrated a concern for discursive processes in addition to emphasizing material conditions.Includes bibliographical reference
Spacetime Coarse Grainings in the Decoherent Histories Approach to Quantum Theory
We investigate the possibility of assigning consistent probabilities to sets
of histories characterized by whether they enter a particular subspace of the
Hilbert space of a closed system during a given time interval. In particular we
investigate the case that this subspace is a region of the configuration space.
This corresponds to a particular class of coarse grainings of spacetime
regions. We consider the arrival time problem and the problem of time in
reparametrization invariant theories as for example in canonical quantum
gravity. Decoherence conditions and probabilities for those application are
derived. The resulting decoherence condition does not depend on the explicit
form of the restricted propagator that was problematic for generalizations such
as application in quantum cosmology. Closely related is the problem of
tunnelling time as well as the quantum Zeno effect. Some interpretational
comments conclude, and we discuss the applicability of this formalism to deal
with the arrival time problem.Comment: 23 pages, Few changes and added references in v
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