Determination of the strangeness content of light-flavour isoscalars from their production rates in hadronic Z decays at LEP

A new phenomenological approach is suggested for determining the strangeness content of light-flavour isoscalars. This approach is based on phenomenological laws of hadron production related to the spin, isospin, strangeness content and mass of the particles. From the total production rates per hadronic Z decay of all light-flavour hadrons, measured so far at LEP, the values of the nonstrange-strange mixing angles are found to be |\phi_P| = 42.3^{\circ} \pm 3.5^{\circ}, |\phi_V| = 10^{\circ} \pm 8^{\circ}, |\phi_T| = 16^{\circ} \pm 11^{\circ} and |\phi_S| = 13^{\circ} \pm 9^{\circ}. Our results on the \eta-\eta^{\prime}, \omega-\phi and f_2-f_2^{\prime} isoscalar mixing are consistent with the present experimental evidence. The strangeness content obtained for the f_0(980) scalar/isoscalar is not consistent with the values supported by recent model studies and is discussed further in the framework of our approach and the K-matrix analysis.Comment: Talk given at the 9th International Conference on Hadron Spectroscopy (Protvino, 2001), 4 pages with 2 figure

Study of charge multiplicity in hadronic three-jet Z decays at LEP

The mean charge multiplicity in hadronic three-jet Z decays has been measured with the DELPHI detector as a function of the event topology and compared with recent theoretical calculations. The QCD colour factor ratio C_A/C_F was determined, and the gluon contribution to this multiplicity was extracted giving a measurement of the mean charge multiplicity of a two-gluon colour-singlet system as a function of the effective c.m. energy covering the range from 16 to 52 GeV.Comment: Talk given at the 32nd International Symposium on Multiparticle Dynamics (ISMD 2002), Alushta, Ukraine, September 7 - 13, 2002; 4 pages with 2 eps-figure

Application of hydrogenation to low-temperature cleaning of the Si(001) surface in the processes of molecular-beam epitaxy: Investigation by STM, RHEED and HRTEM

Structural properties of the clean Si(001) surface obtained as a result of low-temperature (470--650C) pre-growth annealings of silicon wafers in a molecular-beam epitaxy chamber have been investigated. To decrease the cleaning temperature, a silicon surface was hydrogenated in the process of a preliminary chemical treatment in HF and NH_4F aqueous solutions. It has been shown that smooth surfaces composed by wide terraces separated by monoatomic steps can be obtained by dehydrogenation at the temperatures > 600C, whereas clean surfaces obtained at the temperatures < 600C are rough. It has been found that there exists a dependence of structural properties of clean surfaces on the temperature of hydrogen thermal desorption and the process of the preliminary chemical treatment. The frequency of detachment/attachment of Si dimers from/to the steps and effect of the Ehrlich-Schwoebel barrier on ad-dimer migration across steps have been found to be the most probable factors determining a degree of the resultant surface roughness.Comment: 8 pages, 8 figures; version accepted to J. Appl. Phy

N=2 supersymmetric Yang-Mills theory and the superparticle: twistor transform and kappa-symmetry

Lagrangian and Hamiltonian dynamics of de Azcarraga-Lukierski N=2 massive superparticle is considered in the framework of twistor-like Lorentz-harmonic approach. The emphasis is on the study of the interaction with external Abelian gauge superfield. The requirement of preservation of all gauge symmetries of the free model including kappa-symmetry yields correct expressions for the superfield strength constraints and determines the form of nonminimal interaction. We also show that for de Azcarraga-Lukierski N=2 massive superparticle the pullback of field strength 2-superform to the superworld line is not integrable in contrast to the massless superparticle.Comment: 16 pages, LaTe

AdS_4 x CP^3 superstring and D=3 N=6 superconformal symmetry

Motivated by the isomorphism between osp(4|6) superalgebra and D=3 N=6 superconformal algebra we consider the superstring action on the AdS_4 x CP^3 background parametrized by D=3 N=6 super-Poincare and CP^3 coordinates supplemented by the coordinates corresponoding to dilatation and superconformal generators. It is also discussed the relation between the degeneracy of fermionic equations of motion and the action kappa-invariance in the framework of the supercoset approach.Comment: revtex, 12 pages. Version accepted to Phys. Rev. D; v4 corrected misprints in Eqs.(65), (71); v5 corrected discussion of Z_4 grading on page