21,703 research outputs found
Quarks, gluons, colour: Facts or fiction?
A general method is presented which allows one to determine from the local
gauge invariant observables of a quantum field theory the underlying particle
and symmetry structures appearing at the lower (ultraviolet) end of the
spatio--temporal scale. Particles which are confined to small scales, i.e., do
not appear in the physical spectrum, can be uncovered in this way without
taking recourse to gauge fields or indefinite metric spaces. In this way
notions such as quark, gluon, colour symmetry and confinement acquire a new and
intrinsic meaning which is stable under gauge or duality transformations. The
method is illustrated by the example of the Schwinger model.Comment: 22 pages, ams-latex; the article had to be replaced because of tex
problems, there are no changes in the tex
A sharpened nuclearity condition for massless fields
A recently proposed phase space condition which comprises information about
the vacuum structure and timelike asymptotic behavior of physical states is
verified in massless free field theory. There follow interesting conclusions
about the momentum transfer of local operators in this model.Comment: 13 pages, LaTeX. As appeared in Letters in Mathematical Physic
Particle Weights and their Disintegration I
The notion of Wigner particles is attached to irreducible unitary
representations of the Poincare group, characterized by parameters m and s of
mass and spin, respectively. However, the Lorentz symmetry is broken in
theories with long-range interactions, rendering this approach inapplicable
(infraparticle problem). A unified treatment of both particles and
infraparticles via the concept of particle weights can be given within the
framework of Local Quantum Physics. They arise as temporal limits of physical
states in the vacuum sector and describe the asymptotic particle content. In
this paper their definition and characteristic properties are worked out in
detail. The existence of the temporal limits is established by use of suitably
defined seminorms which are also essential in proving the characteristic
features of particle weights.Comment: 33 pages, amslatex, mathptm, minor corrections including numbering
schem
Spinor equations in Weyl geometry
In this paper, the Dirac, twistor and Killing equations on Weyl manifolds
with CSpin structures are investigated. A conformal Schr"odinger-Lichnerowicz
formula is presented and used to show integrability conditions for these
equations. By introducing the Killing equation for spinors of arbitrary weight,
the result of Andrei Moroianu in [9] is generalized in the following sense. The
only non-closed Weyl manifolds of dimension greater than 3 that admit solutions
of the real Killing equation are 4-dimensional and non-compact. Any Weyl
manifold of these dimensions admitting a real Killing spinor has to be
Einstein-Weyl.Comment: Latex2.09, 11 page
On Infravacua and Superselection Theory
In the DHR theory of superselection sectors, one usually considers states
which are local excitations of some vacuum state. Here, we extend this analysis
to local excitations of a class of "infravacuum" states appearing in models
with massless particles. We show that the corresponding superselection
structure, the statistics of superselection sectors and the energy-momentum
spectrum are the same as with respect to the vacuum state. (The latter result
is obtained with a novel method of expressing the shape of the spectrum in
terms of properties of local charge transfer cocycles.) These findings provide
evidence to the effect that infravacua are a natural starting point for the
analysis of the superselection structure in theories with long-range forces.Comment: LaTeX, 18 pages, spelling errors correcte
On Infravacua and the Localisation of Sectors
A certain class of superselection sectors of the free massless scalar field
in 3 space dimensions is considered. It is shown that these sectors, which
cannot be localised with respect to the vacuum, acquire a much better
localisation, namely in spacelike cones, when viewed in front of suitable
``infravacuum'' backgrounds. These background states coincide, essentially,
with a class of states introduced by Kraus, Polley and Reents as models for
clouds of infrared radiation.Comment: LaTeX, 18 pages, minor corrections in order to conform with published
versio
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