55,860 research outputs found
The Gribov problem in Noncommutative gauge theory
After reviewing Gribov ambiguity of non-Abelian gauge theories, a phenomenon
related to the topology of the bundle of gauge connections, we show that there
is a similar feature for noncommutative QED over Moyal space, despite the
structure group being Abelian, and we exhibit an infinite number of solutions
for the equation of Gribov copies. This is a genuine effect of noncommutative
geometry which disappears when the noncommutative parameter vanishes.Comment: 14 pages. Prepared for the XXV International Fall Workshop on
Geometry and Physics, Instituto de Estructura de la Materia (CSIC) Madrid,
Spain August 29 - September 02, 201
SL(2,R) Yang-Mills theory on a circle
The kinematics of SL(2,R) Yang-Mills theory on a circle is considered, for
reasons that are spelled out. The gauge transformations exhibit hyperbolic
fixed points, and this results in a physical configuration space with a
non-Hausdorff "network" topology. The ambiguity encountered in canonical
quantization is then much more pronounced than in the compact case, and can not
be resolved through the kind of appeal made to group theory in that case.Comment: 10 pages, Goteborg ITP 94-19, Contains two files: A latex file with
all figures drawn in latex and a tar archive including a slightly modified
latex file (uses psfig) and nicer postscript figures+necessary macro
A sketching interface for 3D modeling of polyhedron
We present an intuitive and interactive freehand sketching interface for 3D polyhedrons reconstruction. The interface mimics sketching with pencil on paper and takes freehand sketches as input directly. The sketching environment is natural by allowing sketching with discontinuous, overlapping and multiple strokes. The input sketch is a natural line drawing with hidden lines removed that depicts a 3D object in an isometric view. The line drawing is interpreted by a series of 2D tidy-up processes to produce a vertex-edge graph for 3D reconstruction. A novel reconstruction approach based on three-line-junction analysis and planarity constraint is then used to approximate the 3D geometry and topology of the graph. The reconstructed object can be transformed so that it can be viewed from different viewpoints for interactive design or as immediate feedback to the designers. A new sketch can then be added to the existing 3D object, and reconstructed into 3D by referring to the existing 3D object from the current viewpoint. The incremental modeling enables a 3D object to be reconstructed from multiple sketching sessions from different viewpoints. However, the interface is limited to reconstructing trihedrons from sketches without T-junctions to avoid ambiguity in the hidden topology determination
Constrained and reconstructing with semi-invisible production at hadron colliders
Mass variable \sqrt{\hat{S}_{min}} and its variants were constructed by
minimising the parton level center of mass energy that is consistent with all
inclusive measurements. They were proposed to have the ability to measure mass
scale of new physics in a fully model independent way. In this work we relax
the criteria by assuming the availability of partial informations of new
physics events and thus constraining this mass variable even further. Starting
with two different classes of production topology, i.e. antler and non-antler,
we demonstrate the usefulness of these variables to constrain the unknown
masses. This discussion is illustrated with different examples, from the
standard model Higgs production and beyond standard model resonance productions
leading to semi-invisible production. We also utilise these constrains to
reconstruct the semi-invisible events with the momenta of invisible particles
and thus improving the measurements to reveal the properties of new physics.Comment: v2: typos corrected, references added; Matches with published
version. 22 pages, 14 figure
Uniqueness of the Fock quantization of scalar fields in spatially flat cosmological spacetimes
We study the Fock quantization of scalar fields in (generically) time
dependent scenarios, focusing on the case in which the field propagation occurs
in --either a background or effective-- spacetime with spatial sections of flat
compact topology. The discussion finds important applications in cosmology,
like e.g. in the description of test Klein-Gordon fields and scalar
perturbations in Friedmann-Robertson-Walker spacetime in the observationally
favored flat case. Two types of ambiguities in the quantization are analyzed.
First, the infinite ambiguity existing in the choice of a Fock representation
for the canonical commutation relations, understandable as the freedom in the
choice of inequivalent vacua for a given field. Besides, in cosmological
situations, it is customary to scale the fields by time dependent functions,
which absorb part of the evolution arising from the spacetime, which is treated
classically. This leads to an additional ambiguity, this time in the choice of
a canonical pair of field variables. We show that both types of ambiguities are
removed by the requirements of (a) invariance of the vacuum under the
symmetries of the three-torus, and (b) unitary implementation of the dynamics
in the quantum theory. In this way, one arrives at a unique class of unitarily
equivalent Fock quantizations for the system. This result provides considerable
robustness to the quantum predictions and renders meaningful the confrontation
with observation.Comment: 15 pages, version accepted for publication in JCA
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