1,193 research outputs found
Focusing of laser-generated ion beams by a plasma cylinder: similarity theory and the thick lens formula
It is shown that plasma-based optics can be used to guide and focus highly
divergent laser-generated ion beams. A hollow cylinder is considered, which
initially contains a hot electron population. Plasma streaming toward the
cylinder axis maintains a focusing electrostatic field due to the positive
radial pressure gradient. The cylinder works as thick lens, whose parameters
are obtained from similarity theory for freely expanding plasma in cylindrical
geometry. Because the lens parameters are energy dependent, the lens focuses a
selected energy range of ions and works as a monochromator. Because the
focusing is due to the quasineutral part of the expanding plasma, the lens
parameters depend on the hot electron temperature only, and not their
density
micrOMEGAs: recent developments
The program micrOMEGAs that calculates the relic density of the lightest
supersymmetric particle (LSP) in the MSSM is presented. The impact of
coannihilation channels and of higher order corrections to Higgs widths is
stressed. The dependence on the RGE code used to calculate the soft parameters
is also discussed.Comment: 5 pages, 2 figures, Talk presented at IDM2002, York, England;
Reference adde
micrOMEGAs : a tool for dark matter studies
micrOMEGAs is a tool for cold dark matter (DM) studies in generic extensions
of the standard model with a R-parity like discrete symmetry that guarantees
the stability of the lightest odd particle. The code computes the DM relic
density, the elastic scattering cross sections of DM on nuclei relevant for
direct detection, and the spectra of positrons, anti-protons and photons
originating from DM annihilation including porpagation of charged cosmic rays.
The cross sections and decay properties of new particles relevant for collider
studies are included as well as constraints from the flavour sector on the
parameter space of supersymmetric models.Comment: 10 pages, Proceedings of LC09, e+e- Physics at the TeV scale and the
Dark Matter connection, Perugia, Italy, 21-24 sept. 200
micrOMEGAs4.1: two dark matter candidates
micrOMEGAs is a code to compute dark matter observables in generic extensions
of the standard model. This version of micrOMEGAs includes a generalization of
the Boltzmann equations to take into account the possibility of two dark matter
candidates. The modification of the relic density calculation to include
interactions between the two DM sectors as well as semi-annihilation is
presented. Both DM signals in direct and indirect detection are computed as
well. An extension of the standard model with two scalar doublets and a singlet
is used as an example.Comment: 13 pages, 1 figur
W+2jets production at Tevatron -- VECBOS and CompHEP comparison
Results of calculation of all subprocesses in proton-antiproton collisions
which contribute to the W+2jets final state are presented at Tevatron energy.
The calculation has been carried out by means of the CompHEP software package.
A detail comparison with VECBOS generator results for cross sections and
various distributions shows an agreement at the level of Monte-Carlo accuracy.
Therefore the additional independent check of VECBOS generator has been done.
In complement to the VECBOS generator a new generator based on CompHEP allows
to study individual subprocesses like or . The last
point is important, for instance, for study part of the background
for single top or Standard Model Higgs signal at Tevatron.Comment: 8 pages including 4 figures as a gzipped postscript fil
Precision measurements, dark matter direct detection and LHC Higgs searches in a constrained NMSSM
We reexamine the constrained version of the Next-to-Minimal Supersymmetric
Standard Model with semi universal parameters at the GUT scale (CNMSSM). We
include constraints from collider searches for Higgs and SUSY particles, upper
bound on the relic density of dark matter, measurements of the muon anomalous
magnetic moment and of B-physics observables as well as direct searches for
dark matter. We then study the prospects for direct detection of dark matter in
large scale detectors and comment on the prospects for discovery of heavy Higgs
states at the LHC.Comment: 22 pages, 8 figures. Note added and references adde
micrOMEGAs: Version 1.3
We present the latest version of micromegas, a code that calculates the relic
density of the lightest supersymmetric particle in the MSSM. All tree-level
processes for the annihilation of the LSP are included as well as all possible
coannihilation processes with neutralinos, charginos, sleptons, squarks and
gluinos. The cross-sections extracted from CalcHEP are calculated exactly using
loop-corrected masses and mixings as specified in the SUSY Les Houches Accord.
Relativistic formulae for the thermal average are used and care is taken to
handle poles and thresholds by adopting specific integration routines. The
input parameters can be either the soft SUSY parameters in a general MSSM or
the parameters of a SUGRA model specified at some high scale (GUT). In the
latter case, a link with Suspect, Softsusy, Spheno and Isajet allows to
calculate the supersymmetric spectrum, Higgs masses, as well as mixing
matrices. Higher-order corrections to Higgs couplings to quark pairs including
QCD as well as some SUSY corrections (deltaMb) are implemented. Routines
calculating (g-2), bsgamma and bsmumu are also included. In particular the
bsgamma routine includes an improved NLO for the SM and the charged Higgs while
the SUSY large tan(beta) effects beyond leading-order are included. This new
version also provides cross-sections for any 2->2 process as well as partial
decay widths for two-body final states in the MSSM allowing for easy simulation
at colliders.Comment: 45 page
Voronoi Particle Merging Algorithm for PIC Codes
We present a new particle-merging algorithm for the particle-in-cell method.
Based on the concept of the Voronoi diagram, the algorithm partitions the phase
space into smaller subsets, which consist of only particles that are in close
proximity in the phase space to each other. We show the performance of our
algorithm in the case of the two-stream instability and the magnetic shower.Comment: 11 figure
Optimization of symbolic evaluation of helicity amplitudes
We present a method for symbolic evaluation of Feynman amplitudes. We
construct special polarization basis for spinor particles which produces
compact expressions for tensor products of basis spinors.Comment: Standard LaTeX, 6 pages. To appear in the proceedings of the Seventh
International Workshop on Advanced Computing and Analysis Technics in Physics
Research (ACAT2000, Fermilab, October 16-20, 2000
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