Mössbauer spectroscopic study of the early crystallization stage of iron(III) hydroxide particles

Mössbauer spectroscopy was used to investigate the early aging stage of iron(III) hydroxide sols prepared by oxidation of Fe(CO)5 in ethanolic solution, followed by vacuum drying at room temperature. One sample was composed of amorphous particles, while two other samples were partially crystallized, either as a result of solvent change or of spontaneous aging. The main results of Mössbauer measurements in the 80-320 K temperature range are: (a) partially crystallized particles exhibit a strong, S-shaped temperature dependence of the quadrupole splitting, in contrast to a weak and linear variation for amorphous particles; (b) the recoilless fraction temperature dependence is affected by vibration of the particles as a whole, with an effective force constant which is smaller for crystallized particles than for amorphous ones. Furthermore, the former exhibit anf-factor discontinuity near 0°C, which is attributed to melting of a surface layer built up during the crystallization process. © 1986.

Rindler and Minkowski particles relationship revisited

We show that the emission of a Minkowski particle by a general class of scalar sources as described by inertial observers corresponds to either the emission or the absorption of a Rindler particle as described by uniformly accelerated observers. Our results are discussed in connection with the current controversy whether uniformly accelerated detectors radiate.

Stars of WIMPs

A class of boson-fermion stars, whose spin-0 and spin-1/2 constituents interact through a U(1) current-current term in the Lagrangian density, is analyzed. It is shown that it describes the low-energy behavior of a system of weakly interacting massive particles (WIMPs) from the leptonic sector of the minimal supersymmetric standard model. In this case the effective coupling constant A is related to the Fermi constant GF.

LEP sensitivities to spontaneous R-parity violating signals

We illustrate the sensitivities of LEP experiments to leptonic signals associated to models where supersymmetry (SUSY) is realized with spontaneous breaking of R-parity. We focus on missing transverse momentum plus acoplanar muon events (p Τ + μ + μ -) arising from lightest neutralino single production xv as well as pair production xx, followed by x decays, where x denotes the lightest neutralino. We show that the integrated luminosity achieved at LEP already starts probing the basic parameters of the theory. We discuss the significance of these constraints for the simplest spontaneous R-parity breaking models and their relevance for future searches of SUSY particles.

Supersymmetric quantum mechanics and the equivalent classical transformation

In the usual supersymmetric quantum mechanics, the supercharges change the eigenfunction from the bosonic to fermionic sector and conversely. The classical correspondent of this transformation is shown to be the addition of a total time derivative of a purely imaginary function to the Lagrangian function of the system.

Signatures of spontaneous breaking of R-parity in gluino cascade decays at LHC

We study the pattern of gluino cascade decays in a class of supersymmetric models where R-parity is spontaneously broken. We give a detailed discussion of the R-parity violating decays of the lightest neutralino, the second lightest neutralino and the lightest chargino. The multi-lepton and same-sign dilepton signal rates expected in these models are compared with those predicted in the Minimal Supersymmetric Standard Model. We show that these rates can be substantially enhanced in broken R-parity models. © 1997 Elsevier Science B.V.

Preparation and characterization of uniform, spherical particles of Y2O2S and Y2O2S:Eu

The preparation of spherical Y2O2S and Y2O2S:Eu particles using a solid-gas reaction of monodispersed precursors with elemental sulfur vapor under an argon atmosphere has been investigated. The precursors, undoped and doped yttrium basic carbonates, are synthesized by aging a stock solution containing the respective cation chloride and urea at 82-84 °C. Y2O2S and Y2O2S:Eu were characterized in terms of their composition, crystallinity and morphology by chemical analysis, X-ray powder diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The Eu-doped oxysulfide was also characterized by atomic absorption spectrophotometry and luminescence spectroscopy. The spherical morphology of oxysulfide products and of basic carbonate precursors suggests a topotatic inter-relationship between both compounds.

Multilepton signatures for leptoquarks

The production of third generation leptoquarks can give rise to multilepton events accompanied by jets and missing ET. In this work we study the signals of these leptoquarks at the CERN Large Hadron Collider and compare them with the ones expected in supersymmetric models. ©1998 The American Physical Society.

Coordinate-space Faddeev-Hahn-type approach to three-body charge-transfer reactions involving exotic particles

Low-energy muon-transfer cross sections and rates in collisions of muonic atoms with hydrogen isotopes are calculated using a six-state close-coupling approximation to coordinate-space Faddeev-Hahn-type equations. In the muonic case satisfactory results are obtained for all hydrogen isotopes and the experimentaly observed strong isotopic dependence of transfer rates is also reproduced. A comparison with results of other theoretical and available experimental works is presented. The present model also leads to good transfer cross sections in the well-understood problem of antihydrogen formation in antiproton-positronium collision.