50,630 research outputs found
Modular Theory and Eyvind Wichmann's Contributions to modern Particle Physics Theory
Some of the consequences of Eyvind Wichmann's contributions to modular theory
and the QFT phase-space structure are presented. In order to show the power of
those ideas in contemporary problems, I selected the issue of algebraic
holography as well as a new nonperturbative constructive approach (based on the
modular structur of wedge-localized algebras and modular inclusions) and show
that these ideas are recent consequences of the pathbreaking work which
Wichmann together with his collaborator Bisognano initiated in the mid
70$^{ies}.Comment: A rogue address which entered chapter 2 has since been omitted. 21
pages, tcilatex, to be published in a special Festschrift volume, dedicated
to Prof. E. Wichmann on the occasion of his seventieth birthda
Approximation Bounds For Minimum Degree Matching
We consider the MINGREEDY strategy for Maximum Cardinality Matching.
MINGREEDY repeatedly selects an edge incident with a node of minimum degree.
For graphs of degree at most we show that MINGREEDY achieves
approximation ratio at least in the worst case
and that this performance is optimal among adaptive priority algorithms in the
vertex model, which include many prominent greedy matching heuristics. Even
when considering expected approximation ratios of randomized greedy strategies,
no better worst case bounds are known for graphs of small degrees.Comment: % CHANGELOG % rev 1 2014-12-02 % - Show that the class APV contains
many prominent greedy matching algorithms. % - Adapt inapproximability bound
for APV-algorithms to a priori knowledge on |V|. % rev 2 2015-10-31 % -
improve performance guarantee of MINGREEDY to be tigh
Wigner's infinite spin representations and inert matter
Positive energy ray representations of the Poincar\'e group are naturally
subdivided into three classes according to their mass and spin content: m>0,
m=0 finite helicity and m=0 infinite helicity. For a long time the localization
properties of the massless infinite spin class remained unknown before it
became clear that such matter does not permit compact spactime localization and
its generating covariant fields are localized on semi-infinite spacelike
strings. Using a new perturbation theory for higher spin fields we show that
infinite spin matter cannot interact with normal matter and we formulate
condition under which this also could happen for finite spin s>1 fields. This
raises the question of a possible connection between inert matter and dark
matter.Comment: 27 page
Peculiarities of massive vectormesons and their zero mass limits
Massive QED, in contrast with its massless counterpart, possesses two
conserved charges; one is a screened (vanishing) Maxwell charge which is
directly associated with the massive vector mesons through the identically
conserved Maxwell current. A somewhat peculiar situation arises for couplings
of Hermitian matter fields to massive vector potentials; in that case the only
current is the screened Maxwell current and the coupling disappears in the
massless limit. In case of selfinteracting massive vector mesons the situation
becomes even more peculiar in that the usually renormalizability guaranteeing
validity of the first order power-counting criterion breaks down in second
order and requires the compensatory presence of additional Hermitian H-fields.
Some aspect of these observation have already been noticed in the BRST gauge
theoretic formulation, but here we use a new setting based on string-local
vector mesons which is required by Hilbert space positivity. The coupling to
H-fields induces Mexican hat like selfinteractions; they are not imposed and
bear no relation with spontaneous symmetry breaking; they are rather
consequences of the foundational causal localization properties realized in a
Hilbert space setting. In case of selfinteracting massive vectormesons their
presence is required in order to maintain the first order power-counting
restriction of renormalizability also in second order. The presentation of the
new Hilbert space setting for vector mesons which replaces gauge theory and
extends on-shell unitarity to its off-shell counterpart is the main motivation
for this work. The new Hilbert space setting also shows that the second order
Lie-algebra structure of selfinteracting vector mesons is a consequence of the
principles of QFT and promises a deeper understanding of the origin of
confinement.Comment: 34 pages Latex, several additional remarks and citations, improved
formulations, same as published versio
Rotational particle separator: a new method for separating fine particles and mists from gases
An account is given of the patented technique of the rotational particle separator for separating solid and liquid particles of diameter 0.1 µm and larger from gases. Attention is focused on the working principle, fluid mechanical constraints, particle design, separation performance, power consumption, dimensions, filter cleaning and costs. Furthermore, an overview is given of current developments to introduce this technique in industrial dust removal, in electricity generation and in the consumer goods market. The article concludes with a summary of the feature which distinguish this technique from existing filtering methods
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