536 research outputs found
Endomorphism Semigroups and Lightlike Translations
Certain criteria are demonstrated for a spatial derivation of a von Neumann
algebra to generate a one-parameter semigroup of endomorphisms of that algebra.
These are then used to establish a converse to recent results of Borchers and
of Wiesbrock on certain one-parameter semigroups of endomorphisms of von
Neumann algebras (specifically, Type III_1 factors) that appear as lightlike
translations in the theory of algebras of local observables.Comment: 9 pages, Late
The Hot Bang state of massless fermions
In 2002, a method has been proposed by Buchholz et al. in the context of
Local Quantum Physics, to characterize states that are locally in thermodynamic
equilibrium. It could be shown for the model of massless bosons that these
states exhibit quite interesting properties. The mean phase-space density
satisfies a transport equation, and many of these states break time reversal
symmetry. Moreover, an explicit example of such a state, called the Hot Bang
state, could be found, which models the future of a temperature singularity.
However, although the general results carry over to the fermionic case easily,
the proof of existence of an analogue of the Hot Bang state is not quite that
straightforward. The proof will be given in this paper. Moreover, we will
discuss some of the mathematical subtleties which arise in the fermionic case.Comment: 17 page
An Algebraic Jost-Schroer Theorem for Massive Theories
We consider a purely massive local relativistic quantum theory specified by a
family of von Neumann algebras indexed by the space-time regions. We assume
that, affiliated with the algebras associated to wedge regions, there are
operators which create only single particle states from the vacuum (so-called
polarization-free generators) and are well-behaved under the space-time
translations. Strengthening a result of Borchers, Buchholz and Schroer, we show
that then the theory is unitarily equivalent to that of a free field for the
corresponding particle type. We admit particles with any spin and localization
of the charge in space-like cones, thereby covering the case of
string-localized covariant quantum fields.Comment: 21 pages. The second (and crucial) hypothesis of the theorem has been
relaxed and clarified, thanks to the stimulus of an anonymous referee. (The
polarization-free generators associated with wedge regions, which always
exist, are assumed to be temperate.
Limits of magnetic interactions in Ni-Nb ferromagnet-superconductor bilayers
Studies of ferromagnet-superconductor hybrid systems have uncovered magnetic
interactions between the competing electronic orderings. The Electromagnetic
Proximity Effect predicts the formation of a spontaneous vector potential
inside a superconductor placed in proximity to a ferromagnet. In this work, we
use a Nb superconducting layer and Ni ferromagnetic layer to test for such
magnetic interactions. We use the complementary, but independent, techniques of
polarised neutron reflectometry and detection Josephson junctions to probe the
magnetic response inside the superconducting layer at close to zero applied
field. In this condition, Meissner screening is negligible, so our measurements
examine only additional magnetic and screening contributions from proximity
effects. We report that any signals attributable to such proximity effects are
below the detection resolution of our experimental study. We estimate a limit
of the size of the zero field Electromagnetic Proximity Effect in our Ni-Nb
samples to be 0.27 mT from our measurements.Comment: Main text 18 pages, 4 figures, 1 table. Plus SI 8 pages, 6 figure
Semicausal operations are semilocalizable
We prove a conjecture by DiVincenzo, which in the terminology of Preskill et
al. [quant-ph/0102043] states that ``semicausal operations are
semilocalizable''. That is, we show that any operation on the combined system
of Alice and Bob, which does not allow Bob to send messages to Alice, can be
represented as an operation by Alice, transmitting a quantum particle to Bob,
and a local operation by Bob. The proof is based on the uniqueness of the
Stinespring representation for a completely positive map. We sketch some of the
problems in transferring these concepts to the context of relativistic quantum
field theory.Comment: 4 pages, 1 figure, revte
A New Approach to Spin and Statistics
We give an algebraic proof of the spin-statistics connection for the
parabosonic and parafermionic quantum topological charges of a theory of local
observables with a modular PCT-symmetry. The argument avoids the use of the
spinor calculus and also works in 1+2 dimensions. It is expected to be a
progress towards a general spin-statistics theorem including also
(1+2)-dimensional theories with braid group statistics.Comment: LATEX, 15 pages, no figure
Comment on: Modular Theory and Geometry
In this note we comment on part of a recent article by B. Schroer and H.-W.
Wiesbrock. Therein they calculate some new modular structure for the
U(1)-current-algebra (Weyl-algebra). We point out that their findings are true
in a more general setting. The split-property allows an extension to
doubly-localized algebras.Comment: 13 pages, corrected versio
On the Existence of Local Observables in Theories With a Factorizing S-Matrix
A recently proposed criterion for the existence of local quantum fields with
a prescribed factorizing scattering matrix is verified in a non-trivial model,
thereby establishing a new constructive approach to quantum field theory in a
particular example. The existence proof is accomplished by analyzing nuclearity
properties of certain specific subsets of Fermionic Fock spaces.Comment: 13 pages, no figures, comment in sect. 3 adde
The 1990 vertical distribution of two important halons (F-12B1 and F-13B1) in the tropics
The first vertical profiles of F-12B1 and F-13B1 had been obtained in the tropical troposphere and stratosphere by us in 1987. The measurement of these substances responsible for almost the entire anthropogenic contribution to the stratospheric BrO(x) budget is important in the tropics, as tropical upwelling provides their injection along with that of other pollutants, into the stratosphere. To ascertain the trends of these distributions and foster the data, the 1987 experiment was repeated in April 1990. Like 1987, the MPAE cryogenic whole air sampler was launched on a balloon from Hyderabad, India (17.5 deg N), and 14 samples were collected between 10 and 35 km altitude. The results obtained by means of GC and GC-MS analyses showed that the atmospheric abundance of both F-12B1 and F-13B1 is increasing at a fast rate, respectively by about 15 percent and 10 percent per year. From 1987 to 1990, F-12B1 and F-13B1 tropospheric mixing ratios have been growing from 1.2 and 1.3 ppt to 1.8 and 1.7 ppt, respectively. The vertical profiles will be discussed
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