arXiv subjects

Natalia S. Oreshkina

Publications and source records attributed to Natalia S. Oreshkina.

At least 19 recordsLinked to original sources

arXiv2026

Towards better nuclear charge radii

Nuclear charge radii constitute a physical observable of growing significance across multiple subdisciplines of physics and related fields. Their determination relies on a combination of complementary experimental techniques and advanced theoretical frameworks. Current recommended values are informed by the outcomes of several independent working groups, each employing distinct methodological approaches and evaluation strategies. The present effort is directed toward a more precise and reliable extraction of charge radii, as well as the development of a modern, transparent, and methodologically robust compilation of recommended values.

nucl-ex↗

arXiv2026

Wichmann-Kroll Correction in Muonic Atoms and Hydrogen-Like Electronic Ions: a Comparative Study of Two Methods

Wichmann-Kroll corrections are calculated in both hydrogen-like electronic ions and muonic systems ($Z = \{36$--$92\}$) using two independent methods. The Gaussian finite basis set approach, enhanced with dual basis construction, analytical large-distance corrections, and $B$-spline representations, provides computational efficiency. The Green function method, based on semi-analytical construction from Dirac solutions with Fermi nuclear charge distributions, offers higher systematic accuracy and freedom from basis-dependent artifacts. Results are consistent with the literature values, providing reliable reference data for precision spectroscopy of exotic atoms.

physics.atom-ph↗

arXiv2025

Relativistic recoil as a key to the fine-structure puzzle in muonic $^{90}\text{Zr}$

The long-standing fine-structure anomaly in muonic $^{90}$Zr is resolved through a rigorous treatment of the relativistic-recoil effect. From a fit of ab initio QED calculations of the muonic $^{90}$Zr spectrum to precision measurements performed four decades ago, we extract a significantly more precise root-mean-square (rms) charge radius with 6-fold improvement in quality of the fit. A 2-parameter Fermi (2pF) distribution is assumed to model the nuclear charge density and yields a best-fit value of rms charge radius of $r_\text{rms}[^{90}\text{Zr}]=4.2732(7)$ fm ($χ^2 /{\text{DoF}} = 0.995$), in agreement with the previous muonic spectroscopy value, but a factor $6$ more precise, and 3$σ$ larger than the accepted literature value. Additionally, the same analysis has been performed for $^{120}$Sn, where the extracted value of $r_\text{rms}[^{120}\text{Sn}]=4.6518(34)$ fm ($χ^2 /{\text{DoF}} = 0.88$) is consistent with the accepted value. These results confirm our assumption that the muonic fine-structure puzzle arose from an incomplete treatment of QED effects and their uncertainties.

physics.atom-ph↗

arXiv2025

$^{208}$Pb nuclear charge radius revisited: closing the fine-structure-anomaly gap

A comprehensive reevaluation of the root-mean-square nuclear charge radius is presented for the doubly magic $^{208}$Pb extracted from muonic spectroscopy measurements. By integrating rigorous theoretical quantum electrodynamics calculations, state-of-the-art numerical methods, and a systematic reanalysis of the uncertainties, we reduced the long-standing muonic fine-structure anomaly and improved the goodness of fit by a factor of twenty. The resulting value of 5.5062(5)~fm for a Fermi distribution is fairly consistent with the previously reported muonic spectroscopy value, and three standard deviations larger than the commonly used compilation data, which indicates that the current value and its uncertainty could be significantly underestimated. Attributing the remaining discrepancy to theory errors which can not be rigorously calculated we suggest the rms charge radius with reduced model dependence to be 5.5062(17) fm. This work sets an improved benchmark for charge radius extraction in heavy nuclei and paves a path for systematic reevaluations across the nuclear chart.

physics.atom-ph↗

arXiv2025

Hadronic vacuum polarization effect in muonic atoms

The hadronic vacuum polarization (HVP) corrections to energy levels in muonic atoms are studied systematically across the periodic table. Two nuclear charge distribution models have been considered, with partly analytical solution for an homogeneously charged sphere model and direct numerical integration for a Fermi nuclear charge distribution. Our comparison reveals a good agreement between both approaches with differences typically below a few percent. The magnitude of HVP corrections increases with nuclear charge, displaying irregularities that correlate directly with the non-monotonic behavior of nuclear radii. Despite strong relativistic effects at high $Z$, the ratio of hadronic to muonic vacuum polarization remains remarkably stable, deviating by less than $10\%$ from the established $67\%$ non-relativistic benchmark value

physics.atom-ph↗

arXiv2025

Second-order hyperfine structure and its impact on new physics searches using isotope shift spectroscopy

Recent precision isotope shift spectroscopy experiments have reported King plot non-linearities that may uncover previously hidden nuclear properties or hint at new force-carrying bosons. Interpreting the data requires many isotope pairs, but sufficient stable spin-zero nuclei are not always available. In this paper we consider the use of isotopes with non-zero nuclear spin for these studies. We confirm that observed King plot non-linearity in strontium is explained by second-order hyperfine shift in the fermionic nucleus, and we discuss the limitations of using Yb isotopes with non-zero spin in King plot studies. By introducing a specific difference of two isotopes with nuclear spin, we allow for a promising addition to future experimental schemes.

physics.atom-ph↗

arXiv2024

High-accuracy Measurements of Core-excited Transitions in Light Li-like Ions

The transition energies of the two $1s$-core-excited soft X-ray lines (dubbed q and r) from $1s^2 2s ^1S_{1/2}$ to the respective upper levels $1s(^{2}S)2s2p(^{3}P) ^{2}P_{3/2}$ and $^{2}P_{1/2}$ of Li-like oxygen, fluorine and neon were measured and calibrated using several nearby transitions of He-like ions. The major remaining source of energy uncertainties in monochromators, the periodic fluctuations produced by imperfect angular encoder calibration, is addressed by a simultaneously running photoelectron spectroscopy measurement. This leads to an improved energy determination of 5 parts per million, showing fair agreement with previous theories as well as with our own, involving a complete treatment of the autoionizing states studied here. Our experimental results translate to an uncertainty of only 1.6\,km/s for the oxygen line qr-blend used to determine the outflow velocities of active galactic nuclei, ten times smaller than previously possible.

physics.atom-ph↗

arXiv2024

Full leading-order nuclear polarization in highly charged ions

The nuclear-polarization corrections to the energy levels of highly charged ions are systematically investigated to leading order in the fine-structure constant. To this end, the notion of effective photon propagators with nuclear-polarization insertions is employed, where the nuclear excitation spectrum is calculated by means of the Hartree-Fock-based random-phase approximation. The effective Skyrme force is used to describe the interaction between nucleons, and the model dependence is analyzed. To leading order, the formalism predicts two contributions given by the effective vacuum-polarization and self-energy diagrams. The existing ambiguity around the vacuum-polarization term is resolved by demonstrating that it is effectively absorbed in the standard finite-nuclear-size correction. The self-energy part is evaluated with the full electromagnetic electron-nucleus interaction taken into account, where the importance of the effects of the nuclear three-currents is emphasized.

physics.atom-ph↗

arXiv2023

QED calculations of the nuclear recoil effect in muonic atoms

The nuclear recoil effect, known also as the mass shift, is one of theoretical contributions to the energy levels in muonic atoms. Accurate theoretical predictions are therefore needed for extracting e.g. the nuclear charge radii from experimental spectra. We report rigorous QED calculations of the nuclear recoil correction in muonic atoms, carried out to all orders in the nuclear binding strength parameter $Zα$ (where $Z$ is the nuclear charge number and $α$ is the fine structure constant). The calculations show differences with the previous approximate treatment of this effect, most pronounced for the lowest-lying bound states. The calculated recoil correction was found to be sensitive to the nuclear charge radius, which needs to be accounted for when extracting nuclear parameters from the measured spectra.

physics.atom-ph↗

arXiv2023

Nuclear Deformation Effects in the Spectra of Highly Charged Ions

Nuclear deformation effects are theoretically investigated in terms of deformation corrections of the electronic binding and transition energies, $g$ factor, and hyperfine splitting constant. By solving the Dirac equation twice, with the nuclear potential calculated from Fermi and deformed Fermi nuclear density distributions, we separate the deformation effect in binding energies and wavefunctions. The parameters for both models are determined from experimental data. The considered corrections are of interest for spectral analysis and are numerically calculated for the widest possible range of nuclei, consisting over 1100 different samples. The subtleties between different sources of measured data and the corresponding results are discussed. In addition, the importance of deformation effects for the search of new physics with singly-charged ions is examined.

physics.atom-ph↗

arXiv2023

Comment on "Nuclear Excitation by Free Muon Capture"

In the paper [1] the process of free muon capture with simultaneous excitation of a nuclear isomer has been suggested, claiming that ``the effect can be detectable for selected isotopes". Here, we argue that this claim can not be confirmed. Briefly, the process is far from the dominant mechanism for nuclear excitation; it excites high energy nuclear levels that will not generally decay to the isomer; the proposal assumes all incident muons will fulfil energy criteria, ignoring dominant capture paths; and nuclei excited by muons will have a shortened lifetime due to muonic capture.

nucl-th↗

arXiv2022

New Measurement Resolves Key Astrophysical Fe XVII Oscillator Strength Problem

One of the most enduring and intensively studied problems of X-ray astronomy is the disagreement of state-of-the art theory and observations for the intensity ratio of two Fe XVII transitions of crucial value for plasma diagnostics, dubbed 3C and 3D. We unravel this conundrum at the PETRA III synchrotron facility by increasing the resolving power two and a half times and the signal-to-noise ratio thousand-fold compared to our previous work. The Lorentzian wings had hitherto been indistinguishable from the background and were thus not modeled, resulting in a biased line-strength estimation. The present experimental oscillator-strength ratio $R_\mathrm{exp}=f_{\mathrm{3C}}/f_{\mathrm{3D}}=3.51(2)_{\mathrm{stat}}(7)_{\mathrm{sys}}$ agrees with our state-of-the-art calculation of $R_\mathrm{th}=3.55(2)$, as well as with some previous theoretical predictions. To further rule out any uncertainties associated with the measured ratio, we also determined the individual natural linewidths and oscillator strengths of 3C and 3D transitions, which also agree well with the theory. This finally resolves the decades-old mystery of Fe XVII oscillator strengths.

physics.atom-ph↗

arXiv2022

Testing Standard Model extensions with few-electron ions

When collecting spectroscopic data on at least four isotopes, nonlinearities in the King plot are a possible sign of Physics beyond the Standard Model. In this work, an improved approach to the search for hypothetical new interactions with isotope shift spectroscopy of few-electron ions is presented. Very careful account is taken of the small nuclear corrections to the energy levels and the gyromagnetic factors, which cause deviations from King linearity within the Standard Model and are hence a possible source of confounds. In this new approach, the experimental King nonlinearity is not compared to the vanishing prediction of the Standard Model at the leading order, but to the calculated full Standard Model contribution to King nonlinearity. This makes searching for beyond-the-Standard-Model physics with King linearity analysis possible in a very-high-precision experimental regime, avoiding confounds. The bounds which can be set on beyond-the-Standard-Model parameters remain limited by the uncertainties on the small Standard Model nuclear corrections which cause King nonlinearity. Direct comparison between theory and experiment on a single pair of isotopes is advocated as a more suitable approach for few-electron ions.

physics.atom-ph↗

arXiv2022

Self-energy correction to the energy levels of heavy muonic atoms

The first fully relativistic, rigorous QED calculations of the self-energy correction to the fine-structure levels of heavy muonic atoms are reported. We discuss nuclear model and parameter dependence for this contribution as well as numerical convergence issues. The presented results show sizable disagreement with previously reported estimations, including ones used for the determination of the nuclear root-mean-square radii, and underline the importance of rigorous QED calculations for the theoretical prediction of the spectra of muonic atoms.

physics.atom-ph↗

arXiv2022

Evidence against nuclear polarization as source of fine-structure anomalies in muonic atoms

A long-standing problem of fine-structure anomalies in muonic atoms is revisited by considering the $Δ2p$ splitting in muonic $^{90}\mathrm{Zr}$, $^{120}\mathrm{Sn}$ and $^{208}\mathrm{Pb}$ and the $Δ3p$ splitting in muonic $^{208}\mathrm{Pb}$. State-of-the-art techniques from both nuclear and atomic physics are brought together in order to perform the most comprehensive to date calculations of nuclear-polarization energy shifts. Barring the more subtle case of muonic $^{208}\mathrm{Pb}$, the results suggest that the dominant calculation uncertainty is much smaller than the persisting discrepancies between theory and experiment. We conclude that the resolution to the anomalies is likely to be rooted in refined QED corrections or even some other previously unaccounted-for contributions.

physics.atom-ph↗

arXiv2021

Radiative and photon-exchange corrections to New Physics contributions to energy levels in few-electron ions

The influence of hypothetical new interactions beyond the Standard Model on atomic spectra has attracted recent interest. In the present work, interelectronic photon-exchange corrections and radiative quantum electrodynamic corrections to the hypothetical contribution to the energy levels of few-electron ions from a new interaction are calculated. The $1s$, $2s$ and $2p_{1/2}$ ground states of H-like, Li-like and B-like ions are considered, as motivated by proposals to use isotope shift spectroscopy of few-electron ions in order to set stringent constraints on hypothetical new interactions. It is shown that, for light Li-like and B-like ions, photon-exchange corrections are comparable to or even larger, by up to several orders of magnitude, than the leading one-electron contribution from the new interaction, when the latter is mediated by heavy bosons.

physics.atom-ph↗

arXiv2020

Access to the kaon radius with kaonic atoms

We put forward a method for determination of the kaon radius from the spectra of kaonic atoms. We analyze the few lowest transitions and their sensitivity to the size of the kaon for ions in the nuclear charge range Z = 1 - 100, taking into account finite-nuclear-size, finite-kaon-size, recoil and leading-order quantum-electrodynamic effects. Additionally, the opportunities of extracting the kaon mass and nuclear radii are demonstrated by examining the sensitivity of the transition energies in kaonic atoms.

physics.atom-ph↗

arXiv2020

$\textit{Ab initio}$ electronic factors of the $A$ and $B$ hyperfine structure constants for the $5s^25p6s \; ^{1,3}\! P^{\rm o}_{1}$ states in Sn I

Large-scale $\textit{ab initio}$ calculations of the electric field gradient, which constitutes the electronic contribution to the electric quadrupole hyperfine constant $B$, were performed for the $5s^25p6s$ $^{1,3}\!P^{\rm o}_1$ excited states of tin, using three independent computational strategies of the variational multiconfiguration Dirac-Hartree-Fock method and a fourth approach based on the configuration interaction Dirac-Fock-Sturm theory. For the $5s^25p6s$ $^{1}\!P^{\rm o}_1$ state, the final value of $B/Q =703(50)$ MHz/b differs by $0.4\%$ from the one recently used by Yordanov ${\it et~al.}$ [Communications Physics ${\bf 3}$, 107 (2020)] to extract the nuclear quadrupole moments, $Q$, for tin isotopes in the range $^{(117-131)}$Sn from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final $B/Q$ value of the $5s^25p6s\,^{1}\!P^{\rm o}_1$ state based on statistical principles and on correlation with the magnetic dipole hyperfine constant $A$.

physics.atom-ph↗