317 research outputs found
Do macroscopic properties dictate microscopic probabilities?
Aharonov and Reznik have recently (in quant-ph/0110093) argued that the form
of the probabilistic predictions of quantum theory can be seen to follow from
properties of macroscopic systems. An error in their argument is identified.Comment: LaTeX, 6 pages, no figure
Braneworld Dynamics of Inflationary Cosmologies with Exponential Potentials
In this work we consider Randall-Sundrum braneworld type scenarios, in which
the spacetime is described by a five-dimensional manifold with matter fields
confined in a domain wall or three-brane. We present the results of a
systematic analysis, using dynamical systems techniques, of the qualitative
behaviour of Friedmann-Lemaitre-Robertson-Walker type models, whose matter is
described by a scalar field with an exponential potential. We construct the
state spaces for these models and discuss how their structure changes with
respect to the general-relativistic case, in particular, what new critical
points appear and their nature and the occurrence of bifurcation.Comment: 15 pages, 9 figures, RevTex 4. Submitted to Physical Review
Big bang of the brane universe
Big bang of the Friedmann-Robertson-Walker (FRW)-brane universe is studied.
In contrast to the spacelike initial singularity of the usual FRW universe, the
initial singularity of the FRW-brane universe is point-like from the viewpoint
of causality including gravitational waves propagating in the bulk. Existence
of null singularities (seam singuralities) is also shown in the flat and open
FRW-brane universe models.Comment: LaTeX, 11 pages, 3 EPS figure
Brane Junctions in the Randall-Sundrum Scenario
We present static solutions to Einstein's equations corresponding to branes
at various angles intersecting in a single 3-brane. Such configurations may be
useful for building models with localized gravity via the Randall-Sundrum
mechanism. We find that such solutions may exist only if the mechanical forces
acting on the junction exactly cancel. In addition to this constraint there are
further conditions that the parameters of the theory have to satisfy. We find
that at least one of these involves only the brane tensions and cosmological
constants, and thus can not have a dynamical origin. We present these
conditions in detail for two simple examples. We discuss the nature of the
cosmological constant problem in the framework of these scenarios, and outline
the desired features of the brane configurations which may bring us closer
towards the resolution of the cosmological constant problem.Comment: 15 pages, LaTeX. 4 postscript figures included. Typo corrected and
reference adde
A Note on Solitons in Brane Worlds
We obtain the zero mode effective action for gravitating objects in the bulk
of dilatonic domain walls. Without additional fields included in the bulk
action, the zero mode effective action reproduces the action in one lower
dimensions obtained through the ordinary Kaluza-Klein (KK) compactification,
only when the transverse (to the domain wall) component of the bulk metric does
not have non-trivial term depending on the domain wall worldvolume coordinates.
With additional fields included in the bulk action, non-trivial dependence of
the transverse metric component on the domain wall worldvolume coordinates
appears to be essential in reproducing the lower-dimensional action obtained
via the ordinary KK compactification. We find, in particular, that the
effective action for the charged (p+1)-brane in the domain wall bulk reproduces
the action for the p-brane in one lower dimensions.Comment: 13 pages, LaTe
How much time does a measurement take?
We consider the problem of measurement using the Lindblad equation, which
allows the introduction of time in the interaction between the measured system
and the measurement apparatus. We use analytic results, valid for weak
system-environment coupling, obtained for a two-level system in contact with a
measurer (Markovian interaction) and a thermal bath (non-Markovian
interaction), where the measured observable may or may not commute with the
system-environment interaction. Analysing the behavior of the coherence, which
tends to a value asymptotically close to zero, we obtain an expression for the
time of measurement which depends only on the system-measurer coupling, and
which does not depend on whether the observable commutes with the system-bath
interaction. The behavior of the coherences in the case of strong
system-environment coupling, found numerically, indicates that an increase in
this coupling decreases the measurement time, thus allowing our expression to
be considered the upper limit for the duration of the process.Comment: REVISED VERSION: 17 pages, 2 figure
Generalised Israel Junction Conditions for a Gauss-Bonnet Brane World
In spacetimes of dimension greater than four it is natural to consider higher
order (in R) corrections to the Einstein equations. In this letter generalized
Israel junction conditions for a membrane in such a theory are derived. This is
achieved by generalising the Gibbons-Hawking boundary term. The junction
conditions are applied to simple brane world models, and are compared to the
many contradictory results in the literature.Comment: 4 page
Brane cosmological perturbations
We address the question of cosmological perturbations in the context of brane
cosmology, where our Universe is a three-brane where matter is confined,
whereas gravity lives in a higher dimensional spacetime. The equations
governing the bulk perturbations are computed in the case of a general warped
universe. The results are then specialized to the case of a five-dimensional
spacetime, scenario which has recently attracted a lot of attention. In this
context, we decompose the perturbations into `scalar', `vector' and `tensor'
modes, which are familiar in the standard theory of cosmological perturbations.
The junction conditions, which relate the metric perturbations to the matter
perturbations in the brane, are then computed.Comment: 14 pages, Latex; no figur
Consistent histories of systems and measurements in spacetime
Traditional interpretations of quantum theory in terms of wave function
collapse are particularly unappealing when considering the universe as a whole,
where there is no clean separation between classical observer and quantum
system and where the description is inherently relativistic. As an alternative,
the consistent histories approach provides an attractive "no collapse"
interpretation of quantum physics. Consistent histories can also be linked to
path-integral formulations that may be readily generalized to the relativistic
case. A previous paper described how, in such a relativistic spacetime path
formalism, the quantum history of the universe could be considered to be an
eignestate of the measurements made within it. However, two important topics
were not addressed in detail there: a model of measurement processes in the
context of quantum histories in spacetime and a justification for why the
probabilities for each possible cosmological eigenstate should follow Born's
rule. The present paper addresses these topics by showing how Zurek's concepts
of einselection and envariance can be applied in the context of relativistic
spacetime and quantum histories. The result is a model of systems and
subsystems within the universe and their interaction with each other and their
environment.Comment: RevTeX 4; 37 pages; v2 is a revision in response to reviewer
comments, connecting the discussion in the paper more closely to consistent
history concepts; v3 has minor editorial corrections; accepted for
publication in Foundations of Physics; v4 has a couple minor typographical
correction
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