# Publikationen von

Valeriia Kosheleva

Alle Publikationen des HI Jena

## 2022

**g Factor of Lithiumlike Silicon and Calcium: Resolving the Disagreement between Theory and Experiment**

**128**, 103001 (2022)

**Abstract:** The bound-electron g factor is a stringent tool for tests of the standard model and the search for new physics. The comparison between an experiment on the g factor of lithiumlike silicon and the two recent theoretical values revealed the discrepancies of 1.7 sigma [Glazov et al. Phys. Rev. Lett. 123, 173001 (2019)] and 5.2 sigma [Yerokhin et al. Phys. Rev. A 102, 022815 (2020)]. To identify the reason for this disagreement, we accomplish large-scale high-precision computation of the interelectronic-interaction and many-electron QED corrections. The calculations are performed within the extended Furry picture of QED, and the dependence of the final values on the choice of the binding potential is carefully analyzed. As a result, we significantly improve the agreement between the theory and experiment for the g factor of lithiumlike silicon. We also report the most accurate theoretical prediction to date for lithiumlike calcium, which perfectly agrees with the experimental value.

**QED corrections to the hyperfine splitting and g factor of few-electron ions**

Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät (2022)

**Abstract:** Quantum electrodynamics (QED) is the first quantum field theory that describes all phenomena associated with electrically charged particles. Despite its mathematical complexity, it is quite effective in describing and predicting experimental results. With the introduction of lasers, atomic spectroscopy is constantly evolving, contributing to QED testing and continuous improvements in the precision of physical constants determination. Atomic systems offer many opportunities for high-precision QED tests. In the present dissertation, we focus on the magnetic sector of QED: the hyperfine structure and the Zeeman effect in few-electron ions.

We present the systematic QED treatment of the electron correlation effects in the ground-state hyperfine structure in lithiumlike ions for the wide range of nuclear charge numbers Z = 7 - 82. The one- and two-photon exchange corrections are evaluated rigorously within the QED formalism. The electron-correlation contributions due to the exchange by three and more photons are accounted for within the Breit approximation employing the recursive perturbation theory. The calculations are performed in the framework of the extended Furry picture, i.e., with the inclusion of the effective local screening potential in the zeroth-order approximation.

In comparison to previous theoretical computations, we improve the accuracy of the interelectronic-interaction correction to ground-state hyperfine structure in lithiumlike ions. The g factor of a bound electron is a rigorous tool for verifying the Standard Model and searching for new physics. Recently, a measurement of the g factor for lithiumlike silicon was reported and it disagrees by 1.7! with theoretical prediction [D. A. Glazov et al., Phys. Rev. Lett. 123, 173001 (2019)]. Attempting to resolve this deviation another theoretical value for silicon has been delivered. It results in a disagreement with experimental value [V. A. Yerokhin et al., Phys. Rev. A 102, 022815 (2020)]. We perform large-scale high-precision computations of the interelectronic-interaction and many-electron QED corrections to determine the cause of this disagreement. Similar to the case of hyperfine splitting, we carry out the calculations within the extended Furry picture of QED. And we carefully analyze the final values’ dependence on the binding potential. As a result, the agreement between theory and experiment for the g factor of lithiumlike silicon improves significantly. We also present the most accurate theoretical prediction for lithiumlike calcium too, which perfectly agrees with the experimental value.

## 2021

**Redefined vacuum approach and gauge-invariant subsets in two-photon-exchange diagrams for a closed-shell system with a valence electron**

**103**, 042818 (2021)

**Abstract:** CThe two-photon-exchange diagrams for atoms with single valence electrons are investigated. Calculation formulas are derived for an arbitrary state within the rigorous bound-state QED framework utilizing the redefined vacuum formalism. In contrast to other methods, the redefined vacuum approach enables the identification of eight gauge-invariant subsets and, thus, efficiently checks the consistency of the obtained results. The gauge invariance of found subsets is demonstrated both analytically (for an arbitrary state) as well as numerically for 2s, 2p(1/2), and 2p(3/2) valence electrons in Li-like ions. Identifying gauge-invariant subsets in the framework of the proposed approach opens a way to tackle more complex diagrams, e.g., three-photon exchange, where the fragmentation on simpler subsets is crucial for its successful calculation.

## 2020

**Atomic processes with twisted electrons**

**1412**, 052013 (2020)

**Abstract:** The present status of the fully-relativistic nonperturbative calculations of the fundamental atomic processes with twisted electrons is presented. In particular, the elastic (Mott) scattering, the radiative recombination, and for the very first time, the Bremsstrahlung processes are considered. The electron-ion interaction is accounted for in a nonperturbative manner, that allows obtaining reliable results for heavy systems. We investigate the influence of the "twistedness" of the incoming electron on the angular and polarization properties of the emitted electrons and photons for the elastic and inelastic scattering, respectively. It is found that these properties exhibit a strong dependence on the opening angle of the vortex electron beam in all processes considered.

**Resonant two-photon ionization of atoms by twisted and plane-wave light**

**102**, 063115 (2020)

**Abstract:** We study the resonant two-photon ionization of neutral atoms by a combination of twisted and plane-wave light within a fully relativistic framework. In particular, the ionization of an isotropic ensemble of neutral sodium atoms (Z = 11) from their ground 3 S-2(1/2) state via the 3 P-2(3/2) level is considered. We investigate in details the influence of the kinematic parameters of incoming twisted radiation on the photoelectron angular distribution and the circular dichroism. Moreover, we study the influence of the geometry of the process on these quantities. This is done by changing the propagation directions of the incoming twisted and plane-wave light. It is found that the dependence on the kinematic parameters of the twisted photon is the strongest if the plane-wave and twisted light beams are perpendicular to each other.

**Many-electron effects in the hyperfine splitting of lithiumlike ions**

**2**, 013364 (2020)

**Abstract:** The rigorous QED evaluation of the one- and two-photon exchange corrections to the ground-state hyperfine splitting in Li-like ions is presented for the wide range of nuclear charge number Z = 7-82. The calculations are carried out in the framework of the extended Furry picture, i.e., with the inclusion of the effective local screening potential in the zeroth-order approximation. The interelectronic-interaction contributions of the third and higher orders are taken into account in the framework of the Breit approximation employing the recursive perturbation theory. In comparison to the previous theoretical calculations, the accuracy of the interelectronic-interaction contributions to the ground-state hyperfine splitting in Li-like ions is substantially improved.

## 2018

**Elastic scattering of twisted electrons by an atomic target: Going beyond the Born approximation**

**98**, 022706 (2018)

**Abstract:** The elastic scattering of twisted electrons by neutral atoms is studied within the fully relativistic framework. The electron-atom interaction is taken into account in all orders, thus allowing us to explore high-order effects beyond the first Born approximation. To illustrate these effects, detailed calculations of the total and differential cross sections as well as the degree of polarization of scattered electrons are performed. Together with the analysis of the effects beyond the first Born approximation, we discuss the influence of the kinematic parameters of the incident twisted electrons on the angular and polarization properties of the scattered electrons.