21,989 research outputs found
Maximization of capacity and p-norms for some product channels
It is conjectured that the Holevo capacity of a product channel \Omega
\otimes \Phi is achieved when product states are used as input. Amosov, Holevo
and Werner have also conjectured that the maximal p-norm of a product channel
is achieved with product input states. In this paper we establish both of these
conjectures in the case that \Omega is arbitrary and \Phi is a CQ or QC channel
(as defined by Holevo). We also establish the Amosov, Holevo and Werner
conjecture when \Omega is arbitrary and either \Phi is a qubit channel and p=2,
or \Phi is a unital qubit channel and p is integer. Our proofs involve a new
conjecture for the norm of an output state of the half-noisy channel I \otimes
\Phi, when \Phi is a qubit channel. We show that this conjecture in some cases
also implies additivity of the Holevo capacity
Criteria for Continuous-Variable Quantum Teleportation
We derive an experimentally testable criterion for the teleportation of
quantum states of continuous variables. This criterion is especially relevant
to the recent experiment of Furusawa et al. [Science 282, 706-709 (1998)] where
an input-output fidelity of was achieved for optical coherent
states. Our derivation demonstrates that fidelities greater than 1/2 could not
have been achieved through the use of a classical channel alone; quantum
entanglement was a crucial ingredient in the experiment.Comment: 12 pages, to appear in Journal of Modern Optic
Consequences of covariant kaon dynamics in heavy ion collisions
The influence of the chiral mean field on the kaon dynamics in heavy ion
reactions is investigated. Inside the nuclear medium the kaons are described as
dressed quasi-particles carrying effective masses and momenta. A momentum
dependent part of the interaction which resembles a Lorentz force originates
from spatial components of the vector field and provides an important
contribution to the in-medium kaon dynamics. This contribution is found to
counterbalance the influence of the vector potential on the in-plane flow
to a strong extent. Thus it appears to be difficult to restrict the in-medium
potential from the analysis of the corresponding transverse flow.Comment: 14 pages, RevTex, 3 PS figures, accepted for publication in Phys.
Lett.
Kaon squeeze-out in heavy ion reactions
The squeeze-out phenomenon of and mesons, i.e. the azimuthal
asymmetry of and mesons emitted at midrapidity in heavy ion
reactions, is investigated for beam energies of 1-2 A.GeV. It is found that the
squeeze-out signal is strongly affected by in-medium potentials of these
mesons. The repulsive -nucleus potential gives rise to a pronounced
out-of-plane emission of 's at midrapidity. With the potential we
reproduce well the experimental data of the azimuthal distribution. It is
found that the attractive -nucleus potential cancels to a large extent the
influence of rescattering and reabsorption of the mesons on the
projectile and target residuals (i.e. shadowing). This results in an
azimuthally isotropic emission of the midrapidity mesons with transverse
momentum up to 0.8 GeV/c. Since it is well accepted that the shadowing alone
would lead to a significant out-of-plane preference of particle emission, in
particular at high transverse momenta, the disappearance of the out-of-plane
preference for the mesons can serve as an unambiguous signal of the
attractive potential. We also apply a covariant formalism of the kaon
dynamics to the squeeze-out phenomenon. Discrepancies between the theory and
the experiments and possible solutions are discussed.Comment: 24 pages Latex using Elsevier style, 7 PS figures, accepted for
publication in Euro. Phys. Jour.
Constraints on the relativistic mean field of -isobar in nuclear matter
The effects of the presence of -isobars in nuclear matter are studied
in the framework of relativistic mean-field theory. The existence of stable
nuclei at saturation density imposes constraints on the -isobar
self-energy and thereby on the mean-field coupling constants of the scalar and
vector mesons with -isobars. The range of possible values for the
scalar and vector coupling constants of -isobars with respect to the
nucleon coupling is investigated and compared to recent predictions of QCD
sum-rule calculations.Comment: 8 pages, Latex using Elsevier style, 2 PS figures, minor changes in
revised versio
A CNL for Contract-Oriented Diagrams
We present a first step towards a framework for defining and manipulating
normative documents or contracts described as Contract-Oriented (C-O) Diagrams.
These diagrams provide a visual representation for such texts, giving the
possibility to express a signatory's obligations, permissions and prohibitions,
with or without timing constraints, as well as the penalties resulting from the
non-fulfilment of a contract. This work presents a CNL for verbalising C-O
Diagrams, a web-based tool allowing editing in this CNL, and another for
visualising and manipulating the diagrams interactively. We then show how these
proof-of-concept tools can be used by applying them to a small example
Medium modifications of kaons in pion matter
Kaon in-medium masses and mean-field potentials are calculated in
isotopically symmetric pion matter to one loop of chiral perturbation theory.
The results are extended to RHIC temperatures using experimental data on scattering phase shifts. The kaon in-medium broadening results in an
acceleration of the decay. The increased apparent dilepton
branching of the -mesons, observed recently by NA50, NA49, and the
PHENIX collaborations at RHIC, is interpreted in terms of rescattering of
secondary kaons inside of the pion matter.Comment: 5 pages, 2 figures, revised version accepted for publication in PR
Radial flow of kaon mesons in heavy ion reactions
This work investigates the collective motion of kaons in heavy ion reactions
at SIS energies (about 1-2 GeV/nucleon). A radial collective flow of
mesons is predicted to exist in central Au + Au collisions, which manifests in
a characteristic "shoulder-arm" shape of the transverse mass spectrum of the
midrapidity mesons. The radial flow arises from the repulsive
mean field in nuclear matter. In spite of a strong reabsorption and
rescattering the attractive mean field leads as well to a collective
radial flow of mesons. The radial flow, however, is different from
that of mesons and can be observed by a characteristic "concave"
structure of the transverse mass spectrum of the mesons emitted at
midrapidity. The kaon radial flows can therefore serve as a novel tool for the
investigation of kaon properties in dense nuclear matter.Comment: 30 pages RevTex, 5 PS figures, accepted for publication in Phys. Rev.
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