956 research outputs found
Positivity violation for the lattice Landau gluon propagator
We present explicit numerical evidence of reflection-positivity violation for
the lattice Landau gluon propagator in three-dimensional pure SU(2) gauge
theory. We use data obtained at very large lattice volumes (V = 80^3, 140^3)
and for three different lattice couplings in the scaling region (beta = 4.2,
5.0, 6.0). In particular, we observe a clear oscillatory pattern in the
real-space propagator C(t). We also verify that the (real-space) data show good
scaling in the range t \in [0,3] fm and can be fitted using a Gribov-like form.
The violation of positivity is in contradiction with a stable-particle
interpretation of the associated field theory and may be viewed as a
manifestation of confinement.Comment: 5 pages, 6 figures; minor modifications in the text and in the
bibliograph
Negative-Energy Spinors and the Fock Space of Lattice Fermions at Finite Chemical Potential
Recently it was suggested that the problem of species doubling with
Kogut-Susskind lattice fermions entails, at finite chemical potential, a
confusion of particles with antiparticles. What happens instead is that the
familiar correspondence of positive-energy spinors to particles, and of
negative-energy spinors to antiparticles, ceases to hold for the Kogut-Susskind
time derivative. To show this we highlight the role of the spinorial ``energy''
in the Osterwalder-Schrader reconstruction of the Fock space of non-interacting
lattice fermions at zero temperature and nonzero chemical potential. We
consider Kogut-Susskind fermions and, for comparison, fermions with an
asymmetric one-step time derivative.Comment: 14p
Deceleration of neutral molecules in macroscopic traveling traps
A new type of decelerator is presented where polar neutral molecules are
guided and decelerated using the principle of traveling electric potential
wells, such that molecules are confined in stable three-dimensional traps
throughout. This new decelerator is superior to the best currently operational
decelerator (Scharfenberg et al., Phys.Rev.A 79, 023410(2009)), providing a
substantially larger acceptance even at higher accelerations. The mode of
operation is described and experimentally demonstrated by guiding and
decelerating CO molecules.Comment: 10 pages, 3 figure
Continuum Limit of Spin Models with Continuous Symmetry and Conformal Quantum Field Theory
According to the standard classification of Conformal Quantum Field Theory
(CQFT) in two dimensions, the massless continuum limit of the model at
the Kosterlitz-Thouless (KT) transition point should be given by the massless
free scalar field; in particular the Noether current of the model should be
proportional to (the dual of) the gradient of the massless free scalar field,
reflecting a symmetry enhanced from to . More
generally, the massless continuum limit of a spin model with a symmetry given
by a Lie group should have an enhanced symmetry . We point out
that the arguments leading to this conclusion contain two serious gaps: i) the
possibility of `nontrivial local cohomology' and ii) the possibility that the
current is an ultralocal field. For the model we give analytic
arguments which rule out the first possibility and use numerical methods to
dispose of the second one. We conclude that the standard CQFT predictions
appear to be borne out in the model, but give an example where they
would fail. We also point out that all our arguments apply equally well to any
symmetric spin model, provided it has a critical point at a finite
temperature.Comment: 19 page
A traveling wave decelerator for neutral polar molecules
Recently, a decelerator for neutral polar molecules has been presented that
operates on the basis of macroscopic, three-dimensional, traveling
electrostatic traps (Osterwalder et al., Phys. Rev. A 81, 051401 (2010)). In
the present paper, a complete description of this decelerator is given, with
emphasis on the electronics and the mechanical design. Experimental results
showing the transverse velocity distributions of guided molecules are shown and
compared to trajectory simulations. An assessment of non-adiabatic losses is
made by comparing the deceleration signals from 13-CO with those from 12-CO and
with simulated signals.Comment: 10 pages, 7 figure
Algebraic Quantum Theory on Manifolds: A Haag-Kastler Setting for Quantum Geometry
Motivated by the invariance of current representations of quantum gravity
under diffeomorphisms much more general than isometries, the Haag-Kastler
setting is extended to manifolds without metric background structure. First,
the causal structure on a differentiable manifold M of arbitrary dimension
(d+1>2) can be defined in purely topological terms, via cones (C-causality).
Then, the general structure of a net of C*-algebras on a manifold M and its
causal properties required for an algebraic quantum field theory can be
described as an extension of the Haag-Kastler axiomatic framework.
An important application is given with quantum geometry on a spatial slice
within the causally exterior region of a topological horizon H, resulting in a
net of Weyl algebras for states with an infinite number of intersection points
of edges and transversal (d-1)-faces within any neighbourhood of the spatial
boundary S^2.Comment: 15 pages, Latex; v2: several corrections, in particular in def. 1 and
in sec.
Connes-Lott model building on the two-sphere
In this work we examine generalized Connes-Lott models on the two-sphere. The
Hilbert space of the continuum spectral triple is taken as the space of
sections of a twisted spinor bundle, allowing for nontrivial topological
structure (magnetic monopoles). The finitely generated projective module over
the full algebra is also taken as topologically non-trivial, which is possible
over . We also construct a real spectral triple enlarging this Hilbert
space to include "particle" and "anti-particle" fields.Comment: 57 pages, LATE
Functional Integral Construction of the Thirring model: axioms verification and massless limit
We construct a QFT for the Thirring model for any value of the mass in a
functional integral approach, by proving that a set of Grassmann integrals
converges, as the cutoffs are removed and for a proper choice of the bare
parameters, to a set of Schwinger functions verifying the Osterwalder-Schrader
axioms. The corresponding Ward Identities have anomalies which are not linear
in the coupling and which violate the anomaly non-renormalization property.
Additional anomalies are present in the closed equation for the interacting
propagator, obtained by combining a Schwinger-Dyson equation with Ward
Identities.Comment: 55 pages, 9 figure
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