770 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
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
Similarity for ultra-relativistic laser plasmas and the optimal acceleration regime
A similarity theory is developed for ultra-relativistic laser-plasmas. It is
shown that the most fundamental S-similarity is valid for both under- and
overdense plasmas. Optimal scalings for laser wake field electron acceleration
are obtained heuristically. The strong message of the present work is that the
bubble acceleration regime [see Pukhov, Meyer-ter-Vehn, Appl. Phys. B, vol. 74,
355 (2002)] satisfies these optimal scalings
Comparison of SUSY spectrum calculations and impact on the relic density constraints from WMAP
We compare results of four public supersymmetric (SUSY) spectrum codes,
Isajet, Softsusy, Spheno and Suspect to estimate the present-day uncertainty in
the calculation of the relic density of dark matter in mSUGRA models. We find
that even for mass differences of about 1% the spread in the obtained relic
densities can be 10%. In difficult regions of the parameter space, such as
large tan(beta) or large m_0, discrepancies in the relic density are much
larger. We also find important differences in the stau co-annihilation region.
We show the impact of these uncertainties on the bounds from WMAP for several
scenarios, concentrating on the regions of parameter space most relevant for
collider phenomenology. We also discuss the case of non-zero A_0 and the stop
co-annihilation region. Moreover, we present a web application for the online
comparison of the spectrum codes.Comment: 26 pages, 6 figures, 10 tables; version to appear in PR
Light mixed sneutrinos as thermal dark matter
In supersymmetric models with Dirac neutrino masses, a left-right mixed
sneutrino can be a viable dark matter candidate. We examine the
MSSM+ parameter space where this is the case with particular
emphasis on light sneutrinos with masses below 10 GeV. We discuss implications
for direct and indirect dark matter searches, including the relevant
uncertainties, as well as consequences for collider phenomenology.Comment: 33 pages, 14 figures; one figure and references adde
Relic density of dark matter in the NMSSM
We present a code to compute the relic density of dark matter in the
Next-to-Minimal Supersymmetric Standard Model (NMSSM). Dominant corrections to
the Higgs masses are calculated with NMHDECAY as well as theoretical and
collider constraints. All neutralino annihilation and coannihilation processes
are then computed with an extended version of micrOMEGAs, taking into acount
higher order corrections to Higgs vertices. We explore the parameter space of
the NMSSM and consider in particular the case of a bino LSP, of a mixed
bino-higgsino LSP and of a singlino LSP. As compared to the MSSM, neutralino
annihilation is often more efficient as it can take place via (additional)
Higgs resonances as well as annihilation into light Higgs states. Models with a
large singlino component can be compatible with WMAP constraints.Comment: 25 pages, 8 figures; one reference added and minor change in
acknowledgement
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