107,704 research outputs found
Safe domain and elementary geometry
A classical problem of mechanics involves a projectile fired from a given
point with a given velocity whose direction is varied. This results in a family
of trajectories whose envelope defines the border of a 'safe' domain. In the
simple cases of a constant force, harmonic potential and Kepler or Coulomb
motion, the trajectories are conic curves whose envelope in a plane is another
conic section which can be derived either by simple calculus or by geometrical
considerations. The case of harmonic forces reveals a subtle property of the
maximal sum of distances within an ellipse.Comment: Also available from http://democrite.in2p3.fr/democrite-0002317
Speculations in hadron spectroscopy
A selected survey is presented of the recent progress in hadron spectroscopy.
This includes spin-singlet charmonium states, excitations of charmonium and
open-charm mesons, double-charm baryons, and pentaquark candidates. Models
proposing exotic bound states or resonances are reviewed. The sector of exotic
mesons with two heavy quarks appears as particularly promising
Elusive multiquark spectroscopy
A review is presented of past and recent attempts to build multiquark states
within current models already describing ordinary mesons and baryons. This
includes: coherence in the chromomagnetic interaction, tetraquarks with two
heavy quarks, Steiner-tree models of confinement, and hadronic molecules, in
particular in the hidden-charm sector. Some emphasis is put on the difficulties
encountered when extrapolating toward higher configurations the dynamics of
confining forces, starting from the simple case of a quark and an antiquark, or
three quarks in a colour singlet
Historical Survey of the Quasi-Nuclear Baryonium
We review ideas and speculations concerning possible bound states or
resonances of the nucleon--antinucleon system.Comment: 12 pages, Talk at the Workshop on Hadron Spectroscopy, Frascati,
Italy, march 199
Recent issues in hadron spectroscopy
A brief survey is presented of recently discovered hadrons, some of them
presumably demonstrating a new kind of internal structure. This includes :
spin-singlet quarkonium, mesons with unexpected mass or width, baryons with two
heavy quarks, and pentaquark candidates. Flavour configurations with a
combination of light and heavy quarks appear as particularly promising.Comment: Based on an invited talk at the session on Subnucleon degrees of
freedo
Positivity domains for pairs of triples of spin observables
Positivity restrains the allowed domains for pairs or triples of spin
observables in polarised reactions. Various domain shapes in
reactions are displayed. Some
methods to determine these domains are mentioned and a new one based on the
anticommutation between two observables is presented.Comment: Talk given by Xavier Artru at "DSPIN-07", XII Workshop on High-Energy
Spin Physics, Dubna, Sept. 3-7, 2007, to appear in the Proceeding
Stability of multiquarks in a simple string model
A simple string model inspired by the strong-coupling regime of Quantum
ChromoDynamics is used as a potential for studying the spectrum of multiquark
systems with two quarks and two antiquarks, with a careful treatment of the
four-body problem. It is found that the ground state is stable, lying below the
threshold for dissociation into two isolated mesons.Comment: 4 pages, 2 figures, Refs. added, typos corrected, discussion
improved, to appear in Phys. Rev.
Graph Laplacians and Stabilization of Vehicle Formations
Control of vehicle formations has emerged as a topic of significant interest to the controls community. In this paper, we merge tools from graph theory and control theory to derive stability criteria for formation stabilization. The interconnection between vehicles (i.e., which vehicles are sensed by other vehicles) is modeled as a graph, and the eigenvalues of the Laplacian matrix of the graph are used in stating a Nyquist-like stability criterion for vehicle formations. The location of the Laplacian eigenvalues can be correlated to the graph structure, and therefore used to identify desirable and undesirable formation interconnection topologies
Comments on "Observation of Long-Range, Near-Side Angular Correlations in Proton-Proton Collisions at the LHC" by the CMS collaboration(arXiv:1009.4122v1 [hep-ex])"
It is the purpose of this note to point out that the CMS observation is in
line with previous observations in particle physics at large transverse momenta
and/or high multiplicities at lower energies, which were interpreted as
possible evidence for quark-gluon plasma (QGP), and to suggest other features
of the QGP observed in A+A collisions such as radial flow and jet quenching,
which should be investigated in p-p collisions in order to provide further
evidence for QGP production
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