21,751 research outputs found
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
Bound states and the classical double copy
We extend the perturbative classical double copy to the analysis of bound
systems. We first obtain the leading order perturbative gluon radiation field
sourced by a system of interacting color charges in arbitrary time dependent
orbits, and test its validity by taking relativistic bremsstrahlung and
non-relativistic bound state limits. By generalizing the color to kinematic
replacement rules recently used in the context of classical bremsstrahlung, we
map the gluon emission amplitude to the radiation fields of dilaton gravity
sourced by interacting particles in generic (self-consistent) orbits. As an
application, we reproduce the leading post-Newtonian radiation fields and
energy flux for point masses in non-relativistic orbits from the double copy of
gauge theory.Comment: 9 pages, 1 figure, minor revisions to section II
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
Baker domains for Newton's method
We show that there exists an entire function without finite asymptotic values
for which the associated Newton function tends to infinity in some invariant
domain. The question whether such a function exists had been raised by Douady.Comment: 8 page
Toward a unified PNT, Part 1: Complexity and context: Key challenges of multisensor positioning
The next generation of navigation and positioning systems must provide greater accuracy and reliability in a range of challenging environments to meet the needs of a variety of mission-critical applications. No single navigation technology is robust enough to meet these requirements on its own, so a multisensor solution is required. Known environmental features, such as signs, buildings, terrain height variation, and magnetic anomalies, may or may not be available for positioning. The system could be stationary, carried by a pedestrian, or on any type of land, sea, or air vehicle. Furthermore, for many applications, the environment and host behavior are subject to change. A multi-sensor solution is thus required. The expert knowledge problem is compounded by the fact that different modules in an integrated navigation system are often supplied by different organizations, who may be reluctant to share necessary design information if this is considered to be intellectual property that must be protected
Violating conformal invariance: Two-dimensional clusters grafted to wedges, cones, and branch points of Riemann surfaces
We present simulations of 2-d site animals on square and triangular lattices
in non-trivial geomeLattice animals are one of the few critical models in
statistical mechanics violating conformal invariance. We present here
simulations of 2-d site animals on square and triangular lattices in
non-trivial geometries. The simulations are done with the newly developed PERM
algorithm which gives very precise estimates of the partition sum, yielding
precise values for the entropic exponent (). In particular, we studied animals grafted to the tips of wedges
with a wide range of angles , to the tips of cones (wedges with the
sides glued together), and to branching points of Riemann surfaces. The latter
can either have sheets and no boundary, generalizing in this way cones to
angles degrees, or can have boundaries, generalizing wedges. We
find conformal invariance behavior, , only for small
angles (), while for
. These scalings hold both for wedges and cones. A heuristic
(non-conformal) argument for the behavior at large is given, and
comparison is made with critical percolation.Comment: 4 pages, includes 3 figure
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