arXiv subjects

A. Surzhykov

Publications and source records attributed to A. Surzhykov.

At least 73 records · Page 4Linked to original sources

arXiv2012

Relativistic configuration-interaction calculation of energy levels of core-excited states in lithium-like ions: argon through krypton

Large-scale relativistic configuration-interaction calculation of energy levels of core-excited states of lithium-like ions is presented. Quantum electrodynamic, nuclear recoil, and frequency-dependent Breit corrections are included in the calculation. The approach is consistently applied for calculating all $n=2$ core-excited states for all lithium-like ions starting from argon ($Z = 18$) and ending with krypton ($Z = 36$). The results obtained are supplemented with systematical estimations of calculation errors and omitted effects.

physics.atom-ph↗

arXiv2012

Comparative study of the electron- and positron-atom bremsstrahlung

Fully relativistic treatment of the electron-atom and positron-atom bremsstrahlung is reported. The calculation is based on the partial-wave expansion of the Dirac scattering states in an external atomic field. A comparison of the electron and positron bremsstrahlung is presented for the single and double differential cross sections and the Stokes parameters of the emitted photon. It is demonstrated that the electron-positron symmetry of the bremsstrahlung spectra, which is nearly exact in the nonrelativistic regime, is to a large extent removed by the relativistic effects.

physics.atom-ph↗

arXiv2012

Parametrization of the angular correlation and degree of linear polarization in two-photon decays of hydrogen-like ions

The two-photon decay in hydrogen-like ions is investigated within the framework of second order perturbation theory and Dirac's relativistic equation. Special attention is paid to the angular correlation of the emitted photons as well as to the degree of linear polarization of one of the two photons, if the second is just observed under given angles. Expressions for the angular correlation and the degree of linear polarization are expanded in terms of $\cosθ$-polynomials, whose coefficients depend on the atomic number and the energy sharing of the emitted photons. The effects of including higher (electric and magnetic) multipoles upon the emitted photon pairs beyond the electric-dipole approximation are also discussed. Calculations of the coefficients are performed for the transitions $2s_{1/2}\rightarrow1s_{1/2}$, $3d_{3/2}\rightarrow1s_{1/2}$ and $3d_{5/2}\rightarrow1s_{1/2}$, along the entire hydrogen isoelectronic sequence ($1\le Z \le 100$).

physics.atom-ph↗

arXiv2012

PEBSI - A Monte Carlo simulator for bremsstrahlung arising from electrons colliding with thin solid-state targets

We present a Monte Carlo code dedicated to the simulation of bremsstrahlung arising in collisions of polarized electrons with thin target foils. The program consists of an electron transport algorithm taking into account elastic electron-nucleus scattering and inelastic collisions with target electrons as well as a treatment of polarized-electron bremsstrahlung emission. Good agreement is found between the predictions of the electron transport code and data stemming from other simulation programs and experiments. In addition, we present first results from the bremsstrahlung simulation which indicate a significant decrease in the degree of linear polarization of bremsstrahlung even for the thinnest gold targets considered.

physics.atom-ph↗

arXiv2012

Bound-free pair production in ultra-relativistic ion collisions at the LHC collider: Analytic approach to the total and differential cross sections

A theoretical investigation of the bound-free electron-positron pair production in relativistic heavy ion collisions is presented. Special attention is paid to the positrons emitted under large angles with respect to the beam direction. The measurement of these positrons in coincidence with the down--charged ions is in principle feasible by LHC experiments. In order to provide reliable estimates for such measurements, we employ the equivalent photon approximation together with the Sauter approach and derive simple analytic expressions for the differential pair--production cross section, which compare favorably to the results of available numerical calculations. Based on the analytic expressions, detailed calculations are performed for collisions of bare Pb$^{82+}$ ions, taking typical experimental conditions of the LHC experiments into account. We find that the expected count rate strongly depends on the experimental parameters and may be significantly enhanced by increasing the positron-detector acceptance cone.

hep-ph↗

arXiv2011

Magnetic Sublevel Population and Alignment for the Excitation of H- and He-like Uranium in Relativistic Collisions

We have measured the alignment of the L-shell magnetic-substates following the K-shell excitation of hydrogen- and helium-like uranium in relativistic collisions with a low-Z gaseous target. Within this experiment the population distribution for the L-shell magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. The results show a very distinctive behavior for the H- and He-like heavy systems. In particular for $K \rightarrow L$ excitation of He-like uranium, a considerable alignment of the L-shell levels was observed. A comparison of our experimental findings with recent rigorous relativistic predictions provides a good qualitative and a reasonable quantitative agreement, emphasizing the importance of the magnetic-interaction and many-body effects in the strong-field domain of high-Z ions.

physics.atom-ph↗

arXiv2011

Relativistic theory of the double photoionization of helium-like atoms

A fully relativistic calculation of the double photoionization of helium-like atoms is presented. The approach is based on the partial-wave representation of the Dirac continuum states and accounts for the retardation in the electron-electron interaction as well as the higher-order multipoles of the absorbed photon. The electron-electron interaction is taken into account to the leading order of perturbation theory. The relativistic effects are shown to become prominent already for the medium-Z ions, changing the shape and the asymptotic behaviour of the photon energy dependence of the ratio of the double-to-single photoionization cross section.

physics.atom-ph↗

arXiv2011

Angular correlations in the two--photon decay of helium--like heavy ions

The two-photon decay of heavy, helium-like ions is investigated based on second-order perturbation theory and Dirac's relativistic equation. Special attention has been paid to the angular emission of the two photons, i.e., how the angular correlation function depends on the shell structure of the ions in their initial and final states. Moreover, the effects from the (electric and magnetic) non-dipole terms in the expansion of the electron-photon interaction are discussed. Detailed calculations have been carried out for the two-photon decay of the $1s2s \, ^1S_0$, $1s2s \, ^3S_1$ and $1s2p \, ^3P_0$ states of helium-like xenon Xe$^{52+}$, gold Au$^{77+}$ and uranium U$^{90+}$ ions.

quant-ph↗

arXiv2011

Inter-electronic interaction effects on the polarization of recombination photons

A theoretical investigation of the radiative capture of an electron into a bound state of heavy, hydrogen-like ion is presented. Special attention is paid to the question of how the linear polarization of the emitted radiation is affected by the inter-electronic interaction effects. An analysis of these effects is performed within both, the screening-potential approximation and the perturbation theory that treats rigorously the electron correlations to the first order in the parameter 1/Z. By making use of these two approaches, detailed calculations are performed for relativistic collisions of hydrogen-like europium Eu^{62+}, bismuth Bi^{82+} and uranium U^{91+} ions with free electron and low-Z atomic targets. Results of the calculations indicate that the two-electron effects may significantly influence the polarization properties of the recombination x-rays; the effect which can be observed by the present-day polarization detectors.

physics.atom-ph↗

arXiv2011

Interelectronic-interaction effects on the two-photon decay rates of heavy He-like ions

Based on a rigorous QED approach a theoretical analysis is performed for the two-photon transitions in heavy He-like ions. Special attention is paid to the interelectronic-interaction corrections to the decay rates that are taken into account within the two-time Green-function method. Detailed calculations are carried out for the two-photon transitions 2^1S_0 -> 1^1S_0 and 2^3S_1 -> 1^1S_0 in He-like ions within the range of nuclear numbers Z=28-92. The total decay rates together with the spectral distributions are given. The obtained results are compared with experimental values and previous calculations.

physics.atom-ph↗

arXiv2011

Calculation of the two-photon decay rates of hydrogen-like ions by using B-polynomials

A new approach is laid out to investigate the two photon atomic transitions. It is based on application of the finite basis solutions constructed from the Bernstein Polynomial (B-Polynomial) sets. We show that such an approach provides a very promising route for the relativistic second- (and even higher-order) calculations since it allows for analytical evaluation of the involved matrices elements. In order to illustrate possible applications of the method and to verify its accuracy, detailed calculations are performed for the 2s_{1/2}-1s_{1/2} transition in neutral hydrogen and hydrogen-like ions, and are compared with the theoretical predictions based on the well-established B-spline-basis-set approach.

math-ph↗

arXiv2011

Young-type interference in projectile-electron loss in energetic ion-molecule collisions

Under certain conditions an electron bound in a fast projectile-ion, colliding with a molecule, interacts mainly with the nuclei and inner shell electrons of atoms forming the molecule. Due to their compact localization in space and distinct separation from each other these molecular centers play in such collisions a role similar to that of optical slits in light scattering leading to pronounced interference in the spectra of the electron emitted from the projectile.

physics.atom-ph↗

arXiv2010

Multi-Instantons and Exact Results III: Unified Description of the Resonances of Even and Odd Anharmonic Oscillators

This is the third article in a series of three papers on the resonance energy levels of anharmonic oscillators. Whereas the first two papers mainly dealt with double-well potentials and modifications thereof [see J. Zinn-Justin and U. D. Jentschura, Ann. Phys. (N.Y.) 313 (2004), pp. 197 and 269], we here focus on simple even and odd anharmonic oscillators for arbitrary magnitude and complex phase of the coupling parameter. A unification is achieved by the use of PT-symmetry inspired dispersion relations and generalized quantization conditions that include instanton configurations. Higher-order formulas are provided for the oscillators of degrees 3 to 8, which lead to subleading corrections to the leading factorial growth of the perturbative coefficients describing the resonance energies. Numerical results are provided, and higher-order terms are found to be numerically significant. The resonances are described by generalized expansions involving intertwined non-analytic exponentials, logarithmic terms and power series. Finally, we summarize spectral properties and dispersion relations of anharmonic oscillators, and their interconnections. The purpose is to look at one of the classic problems of quantum theory from a new perspective, through which we gain systematic access to the phenomenologically significant higher-order terms.

math-ph↗

arXiv2009

Negative continuum effects on the two-photon decay rates of hydrogen-like ions

Two--photon decay of hydrogen--like ions is studied within the framework of second--order perturbation theory, based on relativistic Dirac's equation. Special attention is paid to the effects arising from the summation over the negative--energy (intermediate virtual) states that occurs in such a framework. In order to investigate the role of these states, detailed calculations have been carried out for the $2s_{1/2} - 1s_{1/2}$ and $2p_{1/2} - 1s_{1/2}$ transitions in neutral hydrogen H as well as for hydrogen--like xenon Xe$^{53+}$ and uranium U$^{91+}$ ions. We found that for a correct evaluation of the total and energy--differential decay rates, summation over the negative--energy part of Dirac's spectrum should be properly taken into account both for high--$Z$ and low--$Z$ atomic systems.

physics.atom-ph↗

arXiv2009

Resonant effects on the two-photon emission from hydrogenic ions

A theoretical study the all two-photon transitions from initial bound states with ni = 2, 3 in hydrogenic ions is presented. High-precision values of relativistic decay rates for ions with nuclear charge in the range 1 =< Z =< 92 are obtained through the use of finite basis sets for the Dirac equation constructed from B-splines. We also report the spectral (energy) distributions of several resonant transitions, which exhibit interesting structures, such as zeroes in the emission spectrum, indicating that two-photon emission is strongly suppressed at certain frequencies. We compare two different approaches (the Line Profile Approach (LPA) and the QED approach based on the analysis of the relativistic two-loop self energy (TLA)) to regularize the resonant contribution to the decay rate. Predictions for the pure two-photon contributions obtained in these approaches are found to be in a good numerical agreement.

physics.atom-ph↗

arXiv2009

Polarization studies on the two-step radiative recombination of highly-charged, heavy ions

The radiative recombination of a free electron into an excited state of a bare, high-Z ion is studied, together with its subsequent decay, within the framework of the density matrix theory and Dirac's relativistic equation. Special attention is paid to the polarization and angular correlations between the recombination and the decay photons. In order to perform a systematic analysis of these correlations the general expression for the double-differential recombination cross section is obtained by making use of the resonance approximation. Based on this expression, detailed computations for the linear polarization of x-ray photons emitted in the (e, 2γ) two-step recombination of uranium ions U^92+ are carried out for a wide range of projectile energies.

physics.atom-ph↗

arXiv2009

Unified Treatment of Even and Odd Anharmonic Oscillators of Arbitrary Degree

We present a unified treatment, including higher-order corrections, of anharmonic oscillators of arbitrary even and odd degree. Our approach is based on a dispersion relation which takes advantage of the PT-symmetry of odd potentials for imaginary coupling parameter, and of generalized quantization conditions which take into account instanton contributions. We find a number of explicit new results, including the general behaviour of large-order perturbation theory for arbitrary levels of odd anharmonic oscillators, and subleading corrections to the decay width of excited states for odd potentials, which are numerically significant.

math-ph↗

arXiv2008

Structure, Time Propagation and Dissipative Terms for Resonances

For odd anharmonic oscillators, it is well known that complex scaling can be used to determine resonance energy eigenvalues and the corresponding eigenvectors in complex rotated space. We briefly review and discuss various methods for the numerical determination of such eigenvalues, and also discuss the connection to the case of purely imaginary coupling, which is PT-symmetric. Moreover, we show that a suitable generalization of the complex scaling method leads to an algorithm for the time propagation of wave packets in potentials which give rise to unstable resonances. This leads to a certain unification of the structure and the dynamics. Our time propagation results agree with known quantum dynamics solvers and allow for a natural incorporation of structural perturbations (e.g., due to dissipative processes) into the quantum dynamics.

math-ph↗