Mixed Valence Europium Nitridosilicate Eu2SiN3

The mixed valence europium nitridosilicate Eu2SiN3 has been synthesized at 900°C in welded tantalum ampules starting from europium and silicon diimide Si(NH)2 in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a=542.3(11) pm, b=1061.0(2) pm, c=1162.9(2) pm, Z=8, 767 independent reflections, 37 parameters, R1=0.017, wR2=0.032). Eu2SiN3 is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN4 tetrahedra running parallel [100] with a maximum stretching factor fs=1.0. The compound is isostructural with Ca2PN3 and Rb2TiO3, and it represents the first example of a nonbranched chain silicate in the class of nitridosilicates. There are two crystallographically distinct europium sites (at two different Wyckoff positions 8f) being occupied with Eu2+ and Eu3+, respectively. 151Eu Mössbauer spectroscopy of Eu2SiN3 differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu2+ and Eu3+ signals over the whole temperature range. The Eu2+ site shows magnetic hyperfine field splitting at 4.2 K. Magnetic susceptibility measurements exhibit Curie-Weiss behavior above 24 K with an effective magnetic moment of 7.5 μB/f.u. and a small contribution of Eu3+, in accordance with Eu2+ and Eu3+ in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at TC=24 K. DFT calculations of Eu2SiN3 reveal a band gap of ∼0.2 eV, which is in agreement with the black color of the compound. Both DFT calculations and lattice energetic calculations (MAPLE) corroborate the assignment of two crystallographically independent Eu sites to Eu2+ and Eu3+

Hard Processes in Electron-Proton Scattering

This report summarizes some of the recent HERA results obtained by studying hard processes in ep-scattering. By resolving the structure of the proton, hard ep-reactions provide information on the parton content of the proton and may give insight into the dynamics of the exchanged parton cascade. In addition, their study offers the possibility to test the Standard Model, in particular perturbative Quantum Chromodynamics, on which the theoretical predictions on ep-scattering cross sections are generally based. Any observed deviation between the data and existing theoretical models would either indicate the need to calculate higher order contributions or hint at signs of new physics.Comment: 15 pages, 8 figures, talk given at 23rd International Conference on Physics in Collision (PIC 2003), Zeuthen, Germany, 26-28 Jun 200

Towards testing a two-Higgs-doublet model with maximal CP symmetry at the LHC: construction of a Monte Carlo event generator

A Monte Carlo event generator is constructed for a two-Higgs-doublet model with maximal CP symmetry, the MCPM. The model contains five physical Higgs bosons; the $\rho'$, behaving similarly to the standard-model Higgs boson, two extra neutral bosons $h'$ and $h"$, and a charged pair $H^\pm$. The special feature of the MCPM is that, concerning the Yukawa couplings, the bosons $h'$, $h"$ and $H^\pm$ couple directly only to the second generation fermions but with strengths given by the third-generation-fermion masses. Our event generator allows the simulation of the Drell-Yan-type production processes of $h'$, $h"$ and $H^\pm$ in proton-proton collisions at LHC energies. Also the subsequent leptonic decays of these bosons into the $\mu^+ \mu^-$, $\mu^+ \nu_\mu$ and $\mu^- \bar \nu_\mu$ channels are studied as well as the dominant background processes. We estimate the integrated luminosities needed in $p p$ collisions at center-of-mass energies of 8 TeV and 14 TeV for significant observations of the Higgs bosons $h'$, $h"$ and $H^\pm$ in these muonic channels

The Missing Odderon

In contrast to theoretical expectations, experimental results at sqrt(s)=200 GeV for the reaction gamma p --> pi0 X show no evidence for odderon exchange. The upper limit on the cross section is an order of magnitude smaller than the theoretical estimate. It is argued that chiral symmetry leads to a large suppression, taking the thoeretical estimates well below the data. Two additional arguments are presented which may decrease the theoretical estimate further. The calculations are more sensitive to the assumptions made in evaluating the hadronic scattering amplitude than in the processes considered previously and lattice gauge calculations indicate that the odderon intercept may be appreciably lower than usually assumed. These two latter effects are particularly relevant for the reactions gamma p --> f2(1270)X and gamma p --> a2(1320)X for which the data upper limits are also below the theoretical predictions, but not so dramatically as for gamma p --> pi0 X.Comment: 12 pages, 3 figure

Human Papillomaviruses in Buschke-Lowenstein Tumors: Physical State of the DNA and Identification of a Tandem Duplication in the Noncoding Region of a Human Papillomavirus 6 Subtype

Six Buschke-Löwenstein tumors, i.e., highly differentiated squamous cell tumors of the genital region, were shown to contain human papillomavirus 6 (HPV 6) or HPV 11 genomes. The viral DNA was found in an episomal state, including a very small fraction of circular oligomers. HPV 6a and HPV 6d genomes were cloned from two of the tumors. Comparison with HPV 6b, cloned from a benign genital wart (E. -M. de Villiers, L. Gissmann, and H. zur Hausen, J. Virol. 40:932-935, 1981) by restriction mapping and partial sequence analysis, revealed a very high degree of homology with the different HPV 6 subtypes. A tandem duplication of 459 base pairs within the noncoding region of the genome was found in the new subtype HPV 6d. This structural rearrangement in a region containing the putative control elements for early gene transcription might influence the biological potential of that virus. No evidence for rearrangement of this region was found in the HPV DNA from the five other tumors