On the nature of the residual meson-meson interaction from simulations with a QED2+1{}_{2+1} model

A potential between mesons is extracted from 4-point functions within lattice gauge theory taking 2+1 dimensional QED as an example. This theory possesses confinement and dynamical fermions. The resulting meson-meson potential has a short-ranged hard repulsive core and the expected dipole-dipole forces lead to attraction at intermediate distances. Sea quarks lead to a softer form of the total potential.Comment: 4 pages, uuencoded tar-compressed postscript file, contribution to Lattice'9

Cross section and analyzing power of pol{p}p -> pn pi+ near threshold

The cross section and analyzing power of the pol{p}p -> pn pi+ reaction near threshold are estimated in terms of data obtained from the pol{p}p -> d pi+ and pp -> pp pi0 reactions. A simple final state interaction theory is developed which depends weakly upon the form of the pion-production operator and includes some Coulomb corrections. Within the uncertainties of the model and the input data, the approach reproduces well the measured energy dependence of the total cross section and the proton analyzing power at a fixed pion c.m. angle of 90deg, from threshold to T_p = 330 MeV. The variation of the differential cross section with pion angle is also very encouraging.Comment: 20 pages, Latex including 4 eps figure

Extraction of hadron-hadron potentials on the lattice within 2+1 dimensional QED

A potential between mesons is extracted from 4-point functions within lattice gauge theory taking 2+1 dimensional QED as an example. This theory possesses confinement and dynamical fermions. The resulting meson-meson potential has a short-ranged hard repulsive core due to antisymmetrization. The expected dipole-dipole forces lead to attraction at intermediate distances. Sea quarks lead to a softer form of the total potential.Comment: 12 pages, uuencoded tar-compressed postscript fil

The Wide-Field X and Gamma-Ray Telescope ECLAIRs aboard the Gamma-Ray Burst Multi-Wavelength Space Mission SVOM

The X and Gamma-ray telescope ECLAIRs is foreseen to be launched on a low Earth orbit (h=630 km, i=30 degrees) aboard the SVOM satellite (Space-based multi-band astronomical Variable Objects Monitor), a French-Chinese mission with Italian contribution. Observations are expected to start in 2013. It has been designed to detect and localize Gamma-Ray Bursts (GRBs) or persistent sources of the sky, thanks to its wide field of view (about 2 sr) and its remarkable sensitivity in the 4-250 keV energy range, with enhanced imaging sensitivity in the 4-70 keV energy band. These characteristics are well suited to detect highly redshifted GRBs, and consequently to provide fast and accurate triggers to other onboard or ground-based instruments able to follow-up the detected events in a very short time from the optical wavelength bands up to the few MeV Gamma-Ray domain.Comment: Proccedings of the "2008 Nanjing GRB Conference", June 23-27 2008, Nanjing, Chin

Magnetic field turbulence in the solar wind at sub-ion scales: in situ observations and numerical simulations

We investigate the transition of the solar wind turbulent cascade from MHD to sub-ion range by means of a detail comparison between in situ observations and hybrid numerical simulations. In particular we focus on the properties of the magnetic field and its component anisotropy in Cluster measurements and hybrid 2D simulations. First, we address the angular distribution of wave-vectors in the kinetic range between ion and electron scales by studying the variance anisotropy of the magnetic field components. When taking into account the single-direction sampling performed by spacecraft in the solar wind, the main properties of the fluctuations observed in situ are also recovered in our numerical description. This result confirms that solar wind turbulence in the sub-ion range is characterized by a quasi-2D gyrotropic distribution of k-vectors around the mean field. We then consider the magnetic compressibility associated with the turbulent cascade and its evolution from large-MHD to sub-ion scales. The ratio of field-aligned to perpendicular fluctuations, typically low in the MHD inertial range, increases significantly when crossing ion scales and its value in the sub-ion range is a function of the total plasma beta only, as expected from theoretical predictions, with higher magnetic compressibility for higher beta. Moreover, we observe that this increase has a gradual trend from low to high beta values in the in situ data; this behaviour is well captured by the numerical simulations. The level of magnetic field compressibility that is observed in situ and in the simulations is in fairly good agreement with theoretical predictions, especially at high beta, suggesting that in the kinetic range explored the turbulence is supported by low-frequency and highly-oblique fluctuations in pressure balance, like kinetic Alfv\'en waves or other slowly evolving coherent structures.Comment: Manuscript submitted to Frontiers Astronomy and Space Sciences, Research Topic: Improving the Understanding of Kinetic Processes in Solar Wind and Magnetosphere: From CLUSTER to MM