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 $T_e$ 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

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+$\tilde\nu_R$ 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

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

Feebly-interacting dark matter

We briefly review scenarios with feebly interacting particles (FIMPs) as dark matter candidates. The discussion covers issues with dark matter production in the early universe as well as signatures of FIMPs at the high energy and high intensity frontier as well as in astroparticle and cosmology.Comment: 6 pages, 2 captioned figures. Review article for EPJ ST Special Issue: Frontier 23: Elementary particle physics, dark matter and astroparticle physic

Has the anomalous single production of the fourth SM family quarks decaying into light Higgs boson been observed by CDF?

Superjet events observed by the CDF Collaboration are interpreted as anomalous single production of the fourth SM family u_4 quark, decaying into a new light scalar particle. The specific predictions of the proposed mechanism are discussed.Comment: 5 pages, 1 tabl