Relativistic corrections to the electric polarizability of compound systems

The widely used relation alpha; = alpha(0)+Deltaalpha for the electric polarizability, where Deltaalpha is proportional to the r.m.s. charge radius of the system, is revisited within a simple model of two spinless particles bound electromagnetically. A complete set of the relativistic corrections to alpha(0) following from the Breit Hamiltonian is obtained. It is shown that these corrections modify the result for alpha; in comparison to that obtained with alpha(0) taken in the nonrelativistic approximation. We propose that the same situation can take place in the more complicated case of hadrons. Special attention is devoted to the correct definition of the center-of-mass coordinates which are found to be very important.     

Magnetoresistance anisotropy in Si /SiGe in tilted magnetic fields: experimental evidence for a stripe-phase formation

We observe pronounced transport anisotropies in magnetotransport experiments performed in the two-dimensional electron system of a Si/SiGe heterostructure. They occur when an in-plane field is used to tune two Landau levels with opposite spin to energetic coincidence. The observed anisotropies disappear drastically for temperatures above 1 K. We propose that our experimental findings may be caused by the formation of a unidirectional stripe phase oriented perpendicular to the in-plane field.     

Novel microscopic mechanism of intermixing during growth on soft metallic substrates

Generic computer simulations using empiric interatomic potentials suggest a new, collective mechanism that could be responsible for mixing at heteroepitaxial interfaces. Even if single adsorbate atoms diffuse by hopping on the substrate surface and do not mix at the terraces, two-dimensional islands formed by nucleation may become unstable above a certain critical size and explode upwards forming clusters of several atomic layers. This process is accompanied by strong distortions of the underlying atomic layers, and on soft materials it can result in surface etching and incorporation of substrate atoms into the islands.     

Prospects for the measurement of the structure of the coupling of a Higgs boson to weak gauge bosons in weak boson fusion with the ATLAS detector

The prospects for the measurement of the tensor structure of the vertex between a standard model Higgs boson and two weak gauge bosons using the distribution of the azimuthal angles between the two tagging jets in the weak boson fusion channel are studied in a Monte Carlo analysis using the fast simulation of the ATLAS detector. The decay channels H→τ⁺τ^-→ll+4ν, H→τ⁺τ^-→lh+3ν at m_H=120 GeV and H→W⁺W^-→llνν at m_H=160 GeV are used in the analysis. For a standard model Higgs boson it is found that purely anomalous couplings are expected to be excluded at a confidence level corresponding to 2σ or more at m_H=120 GeV and more than 5σ at m_H=160 GeV from 30 fb^-1 of data. With a value of 1 roughly reproducing the standard model cross section for a purely anomalous coupling, the standard deviation in a measurement of a contribution of a CP even anomalous coupling in addition to the standard model coupling is estimated to be 0.20 at m_H=120 GeV and 0.09 at m_H=160 GeV.     

Properties of the πη,$ \eta{^\prime}$,σ, f0(980) and a0(980) mesons and their relevance for the polarizabilities of the nucleon

The signs and values of the two-photon couplings F _Mγγ of mesons (M) and their couplings g_MNN to the nucleon as entering into the t -channel parts of the difference of the electromagnetic polarizabilities (α - β) and the backward angle spin polarizabilities γ_π are determined. The excellent agreement achieved with the experimental polarizabilities of the proton makes it possible to make reliable predictions for the neutron. The results obtained are α_n = 13.4±1.0 , β_n = 1.8±1.0 (10^-4fm^3), and γ⁽ⁿ⁾ _π = 57.6±1.8 (10^-4fm^4). New empirical information on the flavor wave functions of the f ₀(980) - and the a ₀(980) -meson is obtained.     

Zur Eintheilung der Strahlencongruenzen 2. Ordnung mit Brennoder singulären Linien; Ebenenbüschel 2. Ordnung in perspectiver Lage zu rationalen Curven

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