Radiative double electron capture by bare nucleus with emission of one photon

Calculation of the cross-section for the process of double electron capture by bare nucleus with emission of a single photon is presented. The double electron capture is evaluated within the framework of Quantum Electrodynamics (QED). Line-Profile Approach (LPA) is employed. Since the radiative double electron capture is governed by the electron correlation, corrections to the interelectron interaction were calculated with high accuracy, partly to all orders of the perturbation theory

Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure

We extend the solid-state nudged elastic band method to handle a non-conserved order parameter - in particular, magnetization, that couples to volume and leads to many observed effects in magnetic systems. We apply this formalism to the well-studied magneto-volume collapse during the pressure-induced transformation in iron - from ferromagnetic body-centered cubic (bcc) austenite to hexagonal close-packed (hcp) martensite. We find a bcc-hcp equilibrium coexistence pressure of 8.4 GPa, with the transition-state enthalpy of 156 meV/Fe at this pressure. A discontinuity in magnetization and coherent stress occurs at the transition state, which has a form of a cusp on the potential-energy surface (yet all the atomic and cell degrees of freedom are continuous); the calculated pressure jump of 25 GPa is related to the observed 25 GPa spread in measured coexistence pressures arising from martensitic and coherency stresses in samples. Our results agree with experiments, but necessarily differ from those arising from drag and restricted parametrization methods having improperly constrained or uncontrolled degrees of freedom.Comment: 7 pages, 7 figure

Electron Bernstein waves in spherical tokamak plasmas with "magnetic wells"

In addition to traditional regimes with monotonously increasing magnetic field, regimes with "magnetic wells" also occur in spherical tokamaks (STs). The magnetic field profile inversion modifies significantly the whole picture of the wave propagation and damping. Since the magnetic wells may become quite common with further improvement of ST performance, analysis of such configurations is of interest for assessment of EBW plasma heating an CD perspectives. In this paper the basic features of the EBWs propagation and damping for the second cyclotron harmonic in a slab model are considered.Comment: Proc. of 13-th Joint Workshop on ECE and ECRH, N.Novgorod, Russia May 17-20, 2004, 8 pages, 4 fig

Nonlinear propagation of light in Dirac matter

The nonlinear interaction between intense laser light and a quantum plasma is modeled by a collective Dirac equation coupled with the Maxwell equations. The model is used to study the nonlinear propagation of relativistically intense laser light in a quantum plasma including the electron spin-1/2 effect. The relativistic effects due to the high-intensity laser light lead, in general, to a downshift of the laser frequency, similar to a classical plasma where the relativistic mass increase leads to self-induced transparency of laser light and other associated effects. The electron spin-1/2 effects lead to a frequency up- or downshift of the electromagnetic (EM) wave, depending on the spin state of the plasma and the polarization of the EM wave. For laboratory solid density plasmas, the spin-1/2 effects on the propagation of light are small, but they may be significant in super-dense plasma in the core of white dwarf stars. We also discuss extensions of the model to include kinetic effects of a distribution of the electrons on the nonlinear propagation of EM waves in a quantum plasma.Comment: 9 pages, 2 figure

On the discrete spectrum of quantum layers

Consider a quantum particle trapped between a curved layer of constant width built over a complete, non-compact, $\mathcal C^2$ smooth surface embedded in $\mathbb{R}^3$. We assume that the surface is asymptotically flat in the sense that the second fundamental form vanishes at infinity, and that the surface is not totally geodesic. This geometric setting is known as a quantum layer. We consider the quantum particle to be governed by the Dirichlet Laplacian as Hamiltonian. Our work concerns the existence of bound states with energy beneath the essential spectrum, which implies the existence of discrete spectrum. We first prove that if the Gauss curvature is integrable, and the surface is weakly $\kappa$-parabolic, then the discrete spectrum is non-empty. This result implies that if the total Gauss curvature is non-positive, then the discrete spectrum is non-empty. We next prove that if the Gauss curvature is non-negative, then the discrete spectrum is non-empty. Finally, we prove that if the surface is parabolic, then the discrete spectrum is non-empty if the layer is sufficiently thin.Comment: Clarifications and corrections to previous version, conjecture from previous version is proven here (Theorem 1.5), additional references include

Effective photon mass and exact translating quantum relativistic structures

Using a variation of the celebrated Volkov solution, the Klein-Gordon equation for a charged particle is reduced to a set of ordinary differential equations, exactly solvable in specific cases. The new quantum relativistic structures can reveal a localization in the radial direction perpendicular to the wave packet propagation, thanks to a non-vanishing scalar potential. The external electromagnetic field, the particle current density and the charge density are determined. The stability analysis of the solutions is performed by means of numerical simulations. The results are useful for the description of a charged quantum test particle in the relativistic regime, provided spin effects are not decisive

Excitation of Spin Waves in Superconducting Ferromagnets

This Letter presents a theoretical analysis of propagation of spin waves in a superconducting ferromagnet. The surface impedance was calculated for the case when the magnetization is normal to the sample surface. We found the frequencies at which the impedance and the power absorption have singularities related to the spin wave propagation, and determined the form of these singularities. With a suitable choice of parameters, there is a frequency interval in which two propagating spin waves of the same circular polarization are generated, one of them having a negative group velocity.Comment: 4 pages, 2 figures, submitted to PR

Spin transfer and current-induced switching in antiferromagnets

We present theoretical description of the precessional switching processes induced by simultaneous application of spin-polarized current and external magnetic field to antiferromagnetic component of the "pinned" layer. We found stability ranges of different static and dynamic regimes. We showed the possibility of steady current-induced precession of antiferromagnetic vector with frequency that linearly depends on the bias current. Furthermore, we found an optimal duration of current pulse required for switching between different orientations of antiferromagnetic vector and current and field dependence of switching time. Our results reveal the difference between dynamics of ferro- and antiferromagnets subjected to spin transfer torques.Comment: 7 pages, 4 figure

Thermodynamics as a nonequilibrium path integral

Thermodynamics is a well developed tool to study systems in equilibrium but no such general framework is available for non-equilibrium processes. Only hope for a quantitative description is to fall back upon the equilibrium language as often done in biology. This gap is bridged by the work theorem. By using this theorem we show that the Barkhausen-type non-equilibrium noise in a process, repeated many times, can be combined to construct a special matrix ${\cal S}$ whose principal eigenvector provides the equilibrium distribution. For an interacting system ${\cal S}$, and hence the equilibrium distribution, can be obtained from the free case without any requirement of equilibrium.Comment: 15 pages, 5 eps files. Final version to appear in J Phys.

Possible Method for Measuring the Proton Form Factors in Processes with and without Proton Spin Flip

The ratio of the squares of the electric and magnetic proton form factors is shown to be proportional to the ratio of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip. The initial proton at rest should be polarized along the direction of the motion of the final proton. Similar results are valid for both radiative $ep$ scattering and the photoproduction of pairs on a proton in the Bethe--Heitler kinematics. When the initial proton is fully polarized in the direction of the motion of the final proton, the cross section for the $ep \to ep$ process, as well as for the $ep \to ep \gamma$ and $\gamma p \to e \bar e p$ processes, without (with) proton spin flip is expressed only in terms of the square of the electric (magnetic) proton form factor. Such an experiment on the measurement of the cross sections without and with proton spin flip would make it possible to acquire new independent data on the behavior of $G_E^2(Q^2)$ and $G_M^2(Q^2)$, which are necessary for resolving the contradictions appearing after the experiment of the JLab collaboration on the measurement of the proton form factors with the method of polarization transfer from the initial electron to the final proton.Comment: 7 pages, revtex