The Z--> l^+ l^- and W--> nu_l l^+ decays in the noncommutative standard model}}

We study Z--> l^+ l^- and W--> nu_l l^+ decays in the standard model including the noncommutative effects. We observe that these effects appear in the flavor dependent part of the decay widths of the processes under consideration and therefore, they are more effective for the heavy lepton decays.Comment: 8 pages, 5 Figure

Anomalous Spin Response and Virtual-Carrier-Mediated Magnetism in a Topological Insulator

We present a comprehensive theoretical study of the static spin response in HgTe quantum wells, revealing distinctive behavior for the topologically nontrivial inverted structure. Most strikingly, the q=0 (long-wave-length) spin susceptibility of the undoped topological-insulator system is constant and equal to the value found for the gapless Dirac-like structure, whereas the same quantity shows the typical decrease with increasing band gap in the normal-insulator regime. We discuss ramifications for the ordering of localized magnetic moments present in the quantum well, both in the insulating and electron-doped situations. The spin response of edge states is also considered, and we extract effective Lande g-factors for the bulk and edge electrons. The variety of counter-intuitive spin-response properties revealed in our study arises from the system's versatility in accessing situations where the charge-carrier dynamics can be governed by ordinary Schrodinger-type physics, mimics the behavior of chiral Dirac fermions, or reflects the material's symmetry-protected topological order.Comment: 15 pages, 8 figures, RevTex4.1; v2: extended and expanded results and presentatio

Collective charge fluctuations and Casimir interactions for quasi one-dimensional metals

We investigate the Casimir interaction between two parallel metallic cylinders and between a metallic cylinder and plate. The material properties of the metallic objects are implemented by the plasma, Drude and perfect metal model dielectric functions. We calculate the Casimir interaction numerically at all separation distances and analytically at large separations. The large-distance asymptotic interaction between one plasma cylinder parallel to another plasma cylinder or plate does not depend on the material properties, but for a Drude cylinder it depends on the dc conductivity $\sigma$. At intermediate separations, for plasma cylinders the asymptotic interaction depends on the plasma wave length $\lambda_{\rm p}$ while for Drude cylinders the Casimir interaction can become independent of the material properties. We confirm the analytical results by the numerics and show that at short separations, the numerical results approach the proximity force approximation

On Guichard's nets and Cyclic systems

In the first part, we give a self contained introduction to the theory of cyclic systems in n-dimensional space which can be considered as immersions into certain Grassmannians. We show how the (metric) geometries on spaces of constant curvature arise as subgeometries of Moebius geometry which provides a slightly new viewpoint. In the second part we characterize Guichard nets which are given by cyclic systems as being Moebius equivalent to 1-parameter families of linear Weingarten surfaces. This provides a new method to study families of parallel Weingarten surfaces in space forms. In particular, analogs of Bonnet's theorem on parallel constant mean curvature surfaces can be easily obtained in this setting.Comment: 25 pages, plain Te

Inception and propagation of positive streamers in high-purity nitrogen: effects of the voltage rise-rate

Controlling streamer morphology is important for numerous applications. Up to now, the effect of the voltage rise rate was only studied across a wide range. Here we show that even slight variations in the voltage rise can have significant effects. We have studied positive streamer discharges in a 16 cm point-plane gap in high-purity nitrogen 6.0, created by 25 kV pulses with a duration of 130 ns. The voltage rise varies by a rise rate from 1.9 kV/ns to 2.7 kV/ns and by the first peak voltage of 22 to 28 kV. A structural link is found between smaller discharges with a larger inception cloud caused by a faster rising voltage. This relation is explained by the greater stability of the inception cloud due to a faster voltage rise, causing a delay in the destabilisation. Time-resolved measurements show that the inception cloud propagates slower than an earlier destabilised, more filamentary discharge. This explains that the discharge with a faster rising voltage pulse ends up to be shorter. Furthermore, the effect of remaining background ionisation in a pulse sequence has been studied, showing that channel thickness and branching rate are locally affected, depending on the covered volume of the previous discharge.Comment: 16 pages, 9 figure

A Normal-Mode Approach to Jovian Atmospheric Dynamics

We propose a nonlinear, quasi-geostrophic, baroclinic model of Jovian atmospheric dynamics, in which vertical variations of velocity are represented by a truncated sum over a complete set of orthogonal functions obtained by a separation of variables of the linearized quasi-geostrophic potential vorticity equation. A set of equations for the time variation of the mode amplitudes in the nonlinear case is then derived. We show that for a planet with a neutrally stable, fluid interior instead of a solid lower boundary, the baroclinic mode represents motions in the interior, and is not affected by the baroclinic modes. One consequence of this is that a normal-mode model with one baroclinic mode is dynamically equivalent to a one layer model with solid lower topography. We also show that for motions in Jupiter's cloudy lower troposphere, the stratosphere behaves nearly as a rigid lid, so that the normal-mode model is applicable to Jupiter. We test the accuracy of the normal-mode model for Jupiter using two simple problem forced, vertically propagating Rossby waves, using two and three baroclinic modes and baroclinic instability, using two baroclinic modes. We find that the normal-road model provide qualitatively correct results, even with only a very limited number of vertical degrees of freedom

Nucleon-nucleon potential in finite nuclei

We consider the spin-isospin-independent central part of the residual nucleon-nucleon potential in finite spherical nuclei taking into account the deformation effects of the nucleons within the surrounding nuclear environment. It is shown that inside the nucleus the short-range repulsive contribution of the potential is increased and the intermediate attraction is decreased. We identify the growth of the radial component of the spin-isospin independent short-range part of the in-medium nucleon-nucleon interaction as the responsible agent that prevents the radial collapse of the nucleus.Comment: 9 pages, 3 eps figure

Time-dependent density functional theory: Past, present, and future

Time-dependent density functional theory (TDDFT) is presently enjoying enormous popularity in quantum chemistry, as a useful tool for extracting electronic excited state energies. This article discusses how TDDFT is much broader in scope, and yields predictions for many more properties. We discuss some of the challenges involved in making accurate predictions for these properties.Comment: 12 pages, 4 figure

Universality versus material dependence of fluctuation forces between metallic wires

We calculate the Casimir interaction between two parallel wires and between a wire and a metall plate. The dielectric properties of the objects are described by the plasma, Drude and perfect metal models. We find that at asymptotically large separation interactions involving plasma wires and/or plates are independent of the material properties, but depend on the dc conductivity $\sigma$ for Drude wires. Counterintuitively, at intermediate separations the interaction involving Drude wires can become independent of $\sigma$. At smaller separations, we compute the interaction numerically and observe an approach to the proximity approximation