arXiv subjects

V. A. Yerokhin

Publications and source records attributed to V. A. Yerokhin.

At least 73 records · Page 4Linked to original sources

arXiv2015

Lamb shift of $n = 1$ and $n = 2$ states of hydrogenlike atoms, $1 \le Z \le 110$

Theoretical energy levels of the $n = 1$ and $n = 2$ states of hydrogenlike atoms with the nuclear charge numbers $1 \le Z \le 110$ are tabulated. The tabulation is based on ab initio quantum electrodynamical calculations performed to all orders in the nuclear binding strength parameter $Zα$, where $α$ is the fine structure constant. Theoretical errors due to various effects are critically examined and estimated.

physics.atom-ph↗

arXiv2014

Relativistic calculations of double $K$-shell photoionization for neutral medium-$Z$ atoms

Fully relativistic calculations are presented for the double $K$-shell photoionization cross section for several neutral medium-$Z$ atoms, from magnesium ($Z = 10$) up to silver ($Z = 47$). The calculations take into account all multipoles of the absorbed photon as well as the retardation of the electron-electron interaction. The approach is based on the partial-wave representation of the Dirac continuum states and uses the Green-function technique to represent the full Dirac spectrum of intermediate states. The method is strictly gauge invariant, which is used as an independent cross check of the computational procedure. The calculated ratios of the double-to-single $K$-shell ionization cross sections are compared with the experimental data and with previous computations.

physics.atom-ph↗

arXiv2014

Relativistic configuration-interaction calculation of $Kα$ transition energies in beryllium-like argon

Relativistic configuration-interaction calculations have been performed for the energy levels of the low-lying and core-excited states of beryllium-like argon, Ar$^{14+}$. These calculations include the one-loop QED effects as obtained by two different methods, the screening-potential approach as well as the model QED operator approach. The calculations are supplemented by a systematic estimation of uncertainties of theoretical predictions.

physics.atom-ph↗

arXiv2014

Relativistic configuration-interaction calculation of $Kα$ transition energies in beryllium-like iron

We perform relativistic configuration-interaction calculations of the energy levels of the low-lying and core-excited states of beryllium-like iron, Fe$^{22+}$. The results include the QED contributions calculated by two different methods, the model QED operator approach and the screening-potential approach. The uncertainties of theoretical energies are estimated systematically. The predicted wavelengths of the Kαtransitions in beryllium-like iron improve previous theoretical results and compare favorably with the experimental data.

physics.atom-ph↗

arXiv2013

Nuclear-size self-energy and vacuum-polarization corrections to the bound-electron g factor

The finite nuclear-size effect on the leading bound-electron g factor and the one-loop QED corrections to the bound-electron g factor is investigated for the ground state of hydrogen-like ions. The calculation is performed to all orders in the nuclear binding strength parameter Zα (where Z is the nuclear charge and α is the fine structure constant) and for the Fermi model of the nuclear charge distribution. In the result, theoretical predictions for the isotope shift of the 1s bound-electron g factor are obtained, which can be used for the determination of the difference of nuclear charge radii from experimental values of the bound-electron g factors for different isotopes.

physics.atom-ph↗

arXiv2013

Two-loop QED corrections with closed fermion loops for the bound-electron g factor

Two-loop QED corrections with closed fermion loops are calculated for the 1s bound-electron g factor. Calculations are performed to all orders in the nuclear binding strength parameter Zα(where Z is the nuclear charge and αis the fine structure constant) except for the closed fermion loop, which is treated within the free-loop (Uehling) approximation in some cases. Comparison with previous Zα-expansion calculations is made and the higher-order remainder of order α^2(Zα)^5 and higher is separated out from the numerical results.

physics.atom-ph↗

arXiv2013

Model operator approach to the Lamb shift calculations in relativistic many-electron atoms

A model operator approach to calculations of the QED corrections to energy levels in relativistic many-electron atomic systems is developed. The model Lamb shift operator is represented by a sum of local and nonlocal potentials which are defined using the results of ab initio calculations of the diagonal and nondiagonal matrix elements of the one-loop QED operator with H-like wave functions. The model operator can be easily included in any calculations based on the Dirac-Coulomb-Breit Hamiltonian. Efficiency of the method is demonstrated by comparison of the model QED operator results for the Lamb shifts in many-electron atoms and ions with exact QED calculations.

physics.atom-ph↗

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

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

Quantum electrodynamic calculation of the hyperfine structure of 3He

The combined fine and hyperfine structure of the $2^3P$ states in $^3$He is calculated within the framework of nonrelativistic quantum electrodynamics. The calculation accounts for the effects of order $mα^6$ and increases the accuracy of theoretical predictions by an order of magnitude. The results obtained are in good agreement with recent spectroscopic measurements in $^3$He.

physics.atom-ph↗

arXiv2012

Frequency metrology of helium around 1083 nm and determination of the nuclear charge radius

We measure the absolute frequency of seven out of the nine allowed transitions between the 2$^3${\it S} and 2$^3${\it P} hyperfine manifolds in a metastable $^3$He beam by using an optical frequency comb synthesizer-assisted spectrometer. The relative uncertainty of our measurements ranges from $1\times 10^{-11}$ to $5\times 10^{-12}$, which is, to our knowledge, the most precise result for any optical $^3$He transition to date. The resulting $2^3${\it P}-2$^3${\it S} centroid frequency is $276\,702\,827\,204.8\,(2.4)$kHz. Comparing this value with the known result for the $^4$He centroid and performing {\em ab initio} QED calculations of the $^4$He-$^3$He isotope shift, we extract the difference of the squared nuclear charge radii $δr^2$ of $^3$He and $^4$He. Our result for $δr^2=1.074 (3)$ fm$^2$ disagrees by about $4\,σ$ with the recent determination [R. van Rooij {\em et al.}, Science {\bf 333}, 196 (2011)].

physics.atom-ph↗

arXiv2012

QED calculation of the nuclear magnetic shielding for hydrogen-like ions

We report an ab initio calculation of the shielding of the nuclear magnetic moment by the bound electron in hydrogen-like ions. This investigation takes into account several effects that have not been calculated before (electron self-energy, vacuum polarization, nuclear magnetization distribution), thus bringing the theory to the point where further progress is impeded by the uncertainty due to nuclear-structure effects. The QED corrections are calculated to all orders in the nuclear binding strength parameter and, independently, to the leading order in the expansion in this parameter. The results obtained lay the ground for the high-precision determination of nuclear magnetic dipole moments from measurements of the g-factor of hydrogen-like 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

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

QED theory of the nuclear magnetic shielding in hydrogen-like ions

The shielding of the nuclear magnetic moment by the bound electron in hydrogen-like ions is calculated ab initio with inclusion of relativistic, nuclear, and quantum electrodynamics (QED) effects. The QED correction is evaluated to all orders in the nuclear binding strength parameter and, independently, to the first order in the expansion in this parameter. The results obtained lay the basis for the high-precision determination of nuclear magnetic dipole moments from measurements of the g-factor of hydrogen-like ions.

physics.atom-ph↗

arXiv2009

QED corrections of order alpha (Zalpha)^2 E_F to the hyperfine splitting of P_1/2 and P_3/2 states in hydrogenlike ions

The hyperfine structure (HFS) of a bound electron is modified by the self-interaction of the electron with its own radiation field. This effect is known as the self-energy correction. In this work, we discuss the evaluation of higher-order self-energy corrections to the HFS of bound P states. These are expressed in a semi-analytic expansion involving powers of Zalpha and ln(Zalpha), where Z is the nuclear charge number and alpha is the fine-structure constant. We find that the correction of relative order alpha (Zalpha)^2 involves only a single logarithm ln(Zalpha) for P_1/2 states [but no term of order alpha (Zalpha)^2 ln^2(Zalpha), whereas for P_3/2 states, even the single logarithm vanishes. By a Foldy-Wouthuysen transformation, we identify a nuclear-spin dependent correction to the electron's transition current, which contributes to the HFS of P states. A comparison of the obtained analytic results to a numerical approach is made.

physics.atom-ph↗

arXiv2009

The two-loop self-energy for the ground state of medium-Z hydrogen-like ions

The two-loop self-energy correction to the ground state Lamb shift is calculated for hydrogen-like ions with the nuclear charge Z=10-30 without any expansion in the binding field of the nucleus. A calculational technique is reported for treatment of Feynman diagrams in the mixed coordinate-momentum representation, which yields significant improvement in numerical accuracy as compared to previous results. An extrapolation of the all-order numerical data towards Z=1 yields a result for the higher-order remainder function for hydrogen. The previously reported disagreement between the all-order and the perturbative approaches is reduced to the marginal agreement.

physics.atom-ph↗