6,955 research outputs found
Assessment and preliminary design of an energy buffer for regenerative braking in electric vehicles
Energy buffer systems, capable of storing the vehicle energy during braking and reusing this stored energy during acceleration, were examined. Some of these buffer systems when incorporated in an electric vehicle would result in an improvement in the performance and range under stop and go driving conditions. Buffer systems considered included flywheels, hydropneumatic, pneumatic, spring, and regenerative braking. Buffer ranking and rating criteria were established. Buffer systems were rated based on predicted range improvements, consumer acceptance, driveability, safety, reliability and durability, and initial and life cycle costs. A hydropneumatic buffer system was selected
Spacelike localization of long-range fields in a model of asymptotic electrodynamics
A previously proposed algebra of asymptotic fields in quantum electrodynamics
is formulated as a net of algebras localized in regions which in general have
unbounded spacelike extension. Electromagnetic fields may be localized in
`symmetrical spacelike cones', but there are strong indications this is not
possible in the present model for charged fields, which have tails extending in
all space directions. Nevertheless, products of appropriately `dressed' fermion
fields (with compensating charges) yield bi-localized observables.Comment: 29 pages, accepted for publication in Annales Henri Poincar\'
Stable quantum systems in anti-de Sitter space: Causality, independence and spectral properties
If a state is passive for uniformly accelerated observers in n-dimensional
anti-de Sitter space-time (i.e. cannot be used by them to operate a perpetuum
mobile), they will (a) register a universal value of the Unruh temperature, (b)
discover a PCT symmetry, and (c) find that observables in complementary
wedge-shaped regions necessarily commute with each other in this state. The
stability properties of such a passive state induce a "geodesic causal
structure" on AdS and concommitant locality relations. It is shown that
observables in these complementary wedge-shaped regions fulfill strong
additional independence conditions. In two-dimensional AdS these even suffice
to enable the derivation of a nontrivial, local, covariant net indexed by
bounded spacetime regions. All these results are model-independent and hold in
any theory which is compatible with a weak notion of space-time localization.
Examples are provided of models satisfying the hypotheses of these theorems.Comment: 27 pages, 1 figure: dedicated to Jacques Bros on the occasion of his
70th birthday. Revised version: typos corrected; as to appear in J. Math.
Phy
The Quest for Understanding in Relativistic Quantum Physics
We discuss the status and some perspectives of relativistic quantum physics.Comment: Invited contribution to the Special Issue 2000 of the Journal of
Mathematical Physics, 38 pages, typos corrected and references added, as to
appear in JM
Quantum Field Theory: Where We Are
We comment on the present status, the concepts and their limitations, and the
successes and open problems of the various approaches to a relativistic quantum
theory of elementary particles, with a hindsight to questions concerning
quantum gravity and string theory.Comment: To appear in: An Assessment of Current Paradigms in the Physics of
Fundamental Phenomena, to be published by Springer Verlag (2006
Continuous Spectrum of Automorphism Groups and the Infraparticle Problem
This paper presents a general framework for a refined spectral analysis of a
group of isometries acting on a Banach space, which extends the spectral theory
of Arveson. The concept of continuous Arveson spectrum is introduced and the
corresponding spectral subspace is defined. The absolutely continuous and
singular-continuous parts of this spectrum are specified. Conditions are given,
in terms of the transposed action of the group of isometries, which guarantee
that the pure-point and continuous subspaces span the entire Banach space. In
the case of a unitarily implemented group of automorphisms, acting on a
-algebra, relations between the continuous spectrum of the automorphisms
and the spectrum of the implementing group of unitaries are found. The group of
spacetime translation automorphisms in quantum field theory is analyzed in
detail. In particular, it is shown that the structure of its continuous
spectrum is relevant to the problem of existence of (infra-)particles in a
given theory.Comment: 31 pages, LaTeX. As appeared in Communications in Mathematical
Physic
On the extension of stringlike localised sectors in 2+1 dimensions
In the framework of algebraic quantum field theory, we study the category
\Delta_BF^A of stringlike localised representations of a net of observables O
\mapsto A(O) in three dimensions. It is shown that compactly localised (DHR)
representations give rise to a non-trivial centre of \Delta_BF^A with respect
to the braiding. This implies that \Delta_BF^A cannot be modular when
non-trival DHR sectors exist. Modular tensor categories, however, are important
for topological quantum computing. For this reason, we discuss a method to
remove this obstruction to modularity.
Indeed, the obstruction can be removed by passing from the observable net
A(O) to the Doplicher-Roberts field net F(O). It is then shown that sectors of
A can be extended to sectors of the field net that commute with the action of
the corresponding symmetry group. Moreover, all such sectors are extensions of
sectors of A. Finally, the category \Delta_BF^F of sectors of F is studied by
investigating the relation with the categorical crossed product of \Delta_BF^A
by the subcategory of DHR representations. Under appropriate conditions, this
completely determines the category \Delta_BF^F.Comment: 36 pages, 1 eps figure; v2: appendix added, minor corrections and
clarification
New Concepts in Particle Physics from Solution of an Old Problem
Recent ideas on modular localization in local quantum physics are used to
clarify the relation between on- and off-shell quantities in particle physics;
in particular the relation between on-shell crossing symmetry and off-shell
Einstein causality. Among the collateral results of this new nonperturbative
approach are profound relations between crossing symmetry of particle physics
and Hawking-Unruh like thermal aspects (KMS property, entropy attached to
horizons) of quantum matter behind causal horizons, aspects which hitherto were
exclusively related with Killing horizons in curved spacetime rather than with
localization aspects in Minkowski space particle physics. The scope of this
modular framework is amazingly wide and ranges from providing a conceptual
basis for the d=1+1 bootstrap-formfactor program for factorizable d=1+1 models
to a decomposition theory of QFT's in terms of a finite collection of unitarily
equivalent chiral conformal theories placed a specified relative position
within a common Hilbert space (in d=1+1 a holographic relation and in higher
dimensions more like a scanning). The new framework gives a spacetime
interpretation to the Zamolodchikov-Faddeev algebra and explains its thermal
aspects.Comment: In this form it will appear in JPA Math Gen, 47 pages tcilate
The Measurement Process in Local Quantum Theory and the EPR Paradox
We describe in a qualitative way a possible picture of the Measurement
Process in Quantum Mechanics, which takes into account: 1. the finite and non
zero time duration T of the interaction between the observed system and the
microscopic part of the measurement apparatus; 2. the finite space size R of
that apparatus; 3. the fact that the macroscopic part of the measurement
apparatus, having the role of amplifying the effect of that interaction to a
macroscopic scale, is composed by a very large but finite number N of
particles. The conventional picture of the measurement, as an instantaneous
action turning a pure state into a mixture, arises only in the limit in which N
and R tend to infinity, and T tends to 0. We sketch here a proposed scheme,
which still ought to be made mathematically precise in order to analyse its
implications and to test it in specific models, where we argue that in Quantum
Field Theory this picture should apply to the unique time evolution expressing
the dynamics of a given theory, and should comply with the Principle of
Locality. We comment on the Einstein Podolski Rosen thought experiment (partly
modifying the discussion on this point in an earlier version of this note),
reformulated here only in terms of local observables (rather than global ones,
as one particle or polarisation observables). The local picture of the
measurement process helps to make it clear that there is no conflict with the
Principle of Locality.Comment: 18 page
Algebraic conformal quantum field theory in perspective
Conformal quantum field theory is reviewed in the perspective of Axiomatic,
notably Algebraic QFT. This theory is particularly developped in two spacetime
dimensions, where many rigorous constructions are possible, as well as some
complete classifications. The structural insights, analytical methods and
constructive tools are expected to be useful also for four-dimensional QFT.Comment: Review paper, 40 pages. v2: minor changes and references added, so as
to match published versio
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