Monthly Notices of the Royal Astronomical Society, 2020
The gravitational potential φ = GM/Rc2 at the surface of the white dwarf G191-B2B is 10,000 times... more The gravitational potential φ = GM/Rc2 at the surface of the white dwarf G191-B2B is 10,000 times stronger than that at the Earth’s surface. Numerous photospheric absorption features are detected, making this a suitable environment to test theories in which the fundamental constants depend on gravity. We have measured the fine structure constant, α, at the white dwarf surface, used a newly calibrated Hubble Space Telescope STIS spectrum of G191-B2B, two new independent sets of laboratory Fe V wavelengths, and new atomic calculations of the sensitivity parameters that quantify Fe V wavelength dependency on α. The two results obtained are: Δα/α0 = (6.36 ± 0.35stat ± 1.84sys) × 10−5 and Δα/α0 = (4.21 ± 0.48stat ± 2.25sys) × 10−5. The measurements hint that the fine structure constant increases slightly in the presence of strong gravitational fields. A comprehensive search for systematic errors is summarised, including possible effects from line misidentifications, line blending, strati...
Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant ... more Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling, and fundamental physics in the search for variation in the fine structure constant. This variation manifests as shifts in the observed wavelengths of absorption lines, such as quadruply ionized iron (FeV) and quadruply ionized nickel (NiV), when compared to laboratory wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801) demonstrated the validity of such an analysis using high-resolution Space Telescope Imaging Spectrograph (STIS) spectra of G191-B2B. We have made three important improvements by: (a) using three new independent sets of laboratory wavelengths; (b) analysing a sample of objects; and (c) improving the methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method). A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. Here we describe our approach and present preliminary results from nine objects using both FeV and NiV.
We performed an extensive study of configuration mixing between the doubly excited (doorway) stat... more We performed an extensive study of configuration mixing between the doubly excited (doorway) states and complex multiply excited states of U 28+ near its ionization threshold. The detailed investigation of complex spectrum and analysis of the statistics of eigenstate components show that the dielectronic (doorway) states weakly mixed with each other. However, they show substantial mixing with the complex multiply excited states. This situation explains the mechanism of low energy electron recombination with U 28+. We calculated the energy averaged capture cross sections as a sum over dielectronic doorway states and found our present calculation interprets well the experimental recombination rates in the energy range of 1 to 100 eV.
We apply a version of the recently developed approach combining the correlation potential, linear... more We apply a version of the recently developed approach combining the correlation potential, linearized singles-doubles coupled-cluster, and the configuration interaction methods to the spectra of the heavy alkaline earths barium, radium, and element 120. Quantum electrodynamics radiative corrections are included. We have found unprecedented agreement between ab initio theory and experiment for the spectra of barium and radium, and we make accurate predictions for missing and unreliable data for all three atoms.
We measure optical spectra of Nd-like W, Re, Os, Ir, and Pt ions of particular interest for studi... more We measure optical spectra of Nd-like W, Re, Os, Ir, and Pt ions of particular interest for studies of a possibly varying fine-structure constant. Exploiting characteristic energy scalings we identify the strongest lines, confirm the predicted 5s-4f level crossing, and benchmark advanced calculations. We infer two possible values for optical M2=E3 and E1 transitions in Ir 17þ that have the highest predicted sensitivity to a variation of the fine-structure constant among stable atomic systems. Furthermore, we determine the energies of proposed frequency standards in Hf 12þ and W 14þ .
Three dominating subsequences of diagrams are summarized: (1) screening of the residual Coulomb i... more Three dominating subsequences of diagrams are summarized: (1) screening of the residual Coulomb interaction; (2) particlehole interaction in the polarization operator; (3) chaining of the self-energy correction. An accuracy of ~ 0.1% is obtained for the caesium energy levels.
The combination of the configuration interaction method and all-order single-double coupledcluste... more The combination of the configuration interaction method and all-order single-double coupledcluster technique is used to calculate excitation energies, ionization potentials and static dipole polarizabilities of superheavy elements nobelium, lawrencium and rutherfordium. Breit and quantum electrodynamic corrections are also included. The results for the superheavy elements are compared with earlier calculations where available. Similar calculations for lighter analogs, ytterbium, lutetium, and hafnium are used to study the accuracy of the calculations. The estimated uncertainties of the final results are discussed.
Using the limit on the value of the electric dipole moment (edm) of the 129Xe atom we obtained th... more Using the limit on the value of the electric dipole moment (edm) of the 129Xe atom we obtained the following bounds on the constants of T-odd interactions: for the electron-nucleon interaction < 4×10-6 GF, for the nucleon-nucleon interaction <GF; the edm of the proton [dp[ <4×10-21 e cm, and the edm of the neutron Idnl _<1×10-21 e cm.
Three dominating subsequences ofdiagrams in the correlation correction are summarized: screening ... more Three dominating subsequences ofdiagrams in the correlation correction are summarized: screening of the residual electronelectron interaction, particle-hole interaction, and the iterations of the self-energy.
It is shown that the Hartree-Fock method provides the exact fulfilment of the Schiff theorem (ext... more It is shown that the Hartree-Fock method provides the exact fulfilment of the Schiff theorem (external electric field shielding at the nucleus). The numerical calculation of the electric field in the Tl+ ion was carried out. The shielded field E
The 7.6 eV electromagnetic transition between the nearly degenerate ground state and first excite... more The 7.6 eV electromagnetic transition between the nearly degenerate ground state and first excited state in the 229 Th nucleus may be very sensitive to potential changes in the fine-structure constant, α = e 2 /hc. However, the sensitivity is not known, and nuclear calculations are currently unable to determine it. We propose measurements of the differences of atomic transition frequencies between thorium atoms (or ions) with the nucleus in the ground state and in the first excited (isomeric) state. This will enable extraction of the change in nuclear charge radius and electric quadrupole moment between the isomers, and hence the α-dependence of the isomeric transition frequency with reasonable accuracy.
We consider microwave hyperfine transitions in the ground state of cesium and rubidium atoms whic... more We consider microwave hyperfine transitions in the ground state of cesium and rubidium atoms which are presently used as the primary and the secondary frequency standards. The atoms are confined in an optical lattice generated by a circularly polarized laser field. We demonstrate that applying an external magnetic field with appropriately chosen direction may cancel dynamic Stark frequency shift making the frequency of the clock transition insensitive to the strengths of both the laser and the magnetic fields. This can be attained for practically any laser frequency which is sufficiently distant from a resonance.
We have performed ab initio calculations of the frequency shift induced by a static electric fiel... more We have performed ab initio calculations of the frequency shift induced by a static electric field on the cesium clock hyperfine transition. The calculations are used to find the frequency shifts due to blackbody radiation. Our result (δν/E 2 = −2.26(2) × 10 −10 Hz/(V/m) 2) is in good agreement with early measurements and ab initio calculations performed in other groups. We present arguments against recent claims that the actual value of the effect might be smaller. The difference (∼ 10%) between ab initio and semiempirical calculations is due to the contribution of the continuum spectrum to the sum over intermediate states.
We explore a feasibility of measuring atom-wall interaction using atomic clocks based on atoms tr... more We explore a feasibility of measuring atom-wall interaction using atomic clocks based on atoms trapped in engineered optical lattices. Optical lattice is normal to the wall. By monitoring the wall-induced clock shift at individual wells of the lattice, one would measure a dependence of the atom-wall interaction on the atom-wall separation. We rigorously evaluate the relevant clock shifts and show that the proposed scheme may uniquely probe the long-range atom-wall interaction in all three qualitatively-distinct regimes of the interaction: van der Waals (image-charge interaction), Casimir-Polder (QED vacuum fluctuations) and Lifshitz (thermal bath fluctuations). The analysis is carried out for atoms Mg, Ca, Sr, Cd, Zn, and Hg, with a particular emphasis on Sr clock.
We propose a new class of atomic microwave clocks based on the hyperfine transitions in the groun... more We propose a new class of atomic microwave clocks based on the hyperfine transitions in the ground state of aluminum or gallium atoms trapped in optical lattices. For these elements magic wavelengths exist at which both levels of the hyperfine doublet are shifted at the same rate by the lattice laser field, cancelling its effect on the clock transition. Our analysis of various systematic effects shows that, while offering an improved control over systematic errors, the accuracy of the proposed microwave clock is competitive to that of the state-of-the-art primary frequency standard.
We have calculated the 6s − 7s parity nonconserving (PNC) E1 transition amplitude, E P N C , in c... more We have calculated the 6s − 7s parity nonconserving (PNC) E1 transition amplitude, E P N C , in cesium. We have used an improved all-order technique in the calculation of the correlations and have included all significant contributions to E P N C. Our final value E P N C = 0.904 1 ± 0.5% × 10 −11 iea B (−Q W /N) has half the uncertainty claimed in old calculations used for the interpretation of Cs PNC experiments. The resulting nuclear weak charge Q W for Cs deviates by about 2σ from the value predicted by the standard model.
The contribution of core nucleons to a static magnetic quadrupole moment is calculated in the pre... more The contribution of core nucleons to a static magnetic quadrupole moment is calculated in the presence of an interaction that violates P and T invariance. The contribution found can be comparable or even larger than the contribution of a valence nucleon, in contrast to the case of the P-violating but T-invariant anapole moment. The core contribution appears to be sensitive to the spin-orbit single-particle potential, which enhances it by a factor of ϳ2. ͓S0556-2813͑96͒04711-5͔
A relativistic method for the calculation of positron binding to atoms is presented. The method c... more A relativistic method for the calculation of positron binding to atoms is presented. The method combines a configuration-interaction treatment of the valence electron and the positron, with a many-body perturbationtheory description of their interaction with the atomic core. We apply this method to positron binding by the copper atom and obtain a binding energy of 170 meV (Ϯ10%). To check the accuracy of the method we use a similar approach to calculate the negative copper ion. The calculated electron affinity is 1.218 eV, in good agreement with the experimental value of 1.236 eV. The problem of convergence of positron-atom bound-state calculations is investigated, and means to improve it are discussed. The relativistic character of the method and its satisfactory convergence make it a suitable tool for heavier atoms. ͓S1050-2947͑99͒08311-0͔
Monthly Notices of the Royal Astronomical Society, 2020
The gravitational potential φ = GM/Rc2 at the surface of the white dwarf G191-B2B is 10,000 times... more The gravitational potential φ = GM/Rc2 at the surface of the white dwarf G191-B2B is 10,000 times stronger than that at the Earth’s surface. Numerous photospheric absorption features are detected, making this a suitable environment to test theories in which the fundamental constants depend on gravity. We have measured the fine structure constant, α, at the white dwarf surface, used a newly calibrated Hubble Space Telescope STIS spectrum of G191-B2B, two new independent sets of laboratory Fe V wavelengths, and new atomic calculations of the sensitivity parameters that quantify Fe V wavelength dependency on α. The two results obtained are: Δα/α0 = (6.36 ± 0.35stat ± 1.84sys) × 10−5 and Δα/α0 = (4.21 ± 0.48stat ± 2.25sys) × 10−5. The measurements hint that the fine structure constant increases slightly in the presence of strong gravitational fields. A comprehensive search for systematic errors is summarised, including possible effects from line misidentifications, line blending, strati...
Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant ... more Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling, and fundamental physics in the search for variation in the fine structure constant. This variation manifests as shifts in the observed wavelengths of absorption lines, such as quadruply ionized iron (FeV) and quadruply ionized nickel (NiV), when compared to laboratory wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801) demonstrated the validity of such an analysis using high-resolution Space Telescope Imaging Spectrograph (STIS) spectra of G191-B2B. We have made three important improvements by: (a) using three new independent sets of laboratory wavelengths; (b) analysing a sample of objects; and (c) improving the methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method). A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. Here we describe our approach and present preliminary results from nine objects using both FeV and NiV.
We performed an extensive study of configuration mixing between the doubly excited (doorway) stat... more We performed an extensive study of configuration mixing between the doubly excited (doorway) states and complex multiply excited states of U 28+ near its ionization threshold. The detailed investigation of complex spectrum and analysis of the statistics of eigenstate components show that the dielectronic (doorway) states weakly mixed with each other. However, they show substantial mixing with the complex multiply excited states. This situation explains the mechanism of low energy electron recombination with U 28+. We calculated the energy averaged capture cross sections as a sum over dielectronic doorway states and found our present calculation interprets well the experimental recombination rates in the energy range of 1 to 100 eV.
We apply a version of the recently developed approach combining the correlation potential, linear... more We apply a version of the recently developed approach combining the correlation potential, linearized singles-doubles coupled-cluster, and the configuration interaction methods to the spectra of the heavy alkaline earths barium, radium, and element 120. Quantum electrodynamics radiative corrections are included. We have found unprecedented agreement between ab initio theory and experiment for the spectra of barium and radium, and we make accurate predictions for missing and unreliable data for all three atoms.
We measure optical spectra of Nd-like W, Re, Os, Ir, and Pt ions of particular interest for studi... more We measure optical spectra of Nd-like W, Re, Os, Ir, and Pt ions of particular interest for studies of a possibly varying fine-structure constant. Exploiting characteristic energy scalings we identify the strongest lines, confirm the predicted 5s-4f level crossing, and benchmark advanced calculations. We infer two possible values for optical M2=E3 and E1 transitions in Ir 17þ that have the highest predicted sensitivity to a variation of the fine-structure constant among stable atomic systems. Furthermore, we determine the energies of proposed frequency standards in Hf 12þ and W 14þ .
Three dominating subsequences of diagrams are summarized: (1) screening of the residual Coulomb i... more Three dominating subsequences of diagrams are summarized: (1) screening of the residual Coulomb interaction; (2) particlehole interaction in the polarization operator; (3) chaining of the self-energy correction. An accuracy of ~ 0.1% is obtained for the caesium energy levels.
The combination of the configuration interaction method and all-order single-double coupledcluste... more The combination of the configuration interaction method and all-order single-double coupledcluster technique is used to calculate excitation energies, ionization potentials and static dipole polarizabilities of superheavy elements nobelium, lawrencium and rutherfordium. Breit and quantum electrodynamic corrections are also included. The results for the superheavy elements are compared with earlier calculations where available. Similar calculations for lighter analogs, ytterbium, lutetium, and hafnium are used to study the accuracy of the calculations. The estimated uncertainties of the final results are discussed.
Using the limit on the value of the electric dipole moment (edm) of the 129Xe atom we obtained th... more Using the limit on the value of the electric dipole moment (edm) of the 129Xe atom we obtained the following bounds on the constants of T-odd interactions: for the electron-nucleon interaction < 4×10-6 GF, for the nucleon-nucleon interaction <GF; the edm of the proton [dp[ <4×10-21 e cm, and the edm of the neutron Idnl _<1×10-21 e cm.
Three dominating subsequences ofdiagrams in the correlation correction are summarized: screening ... more Three dominating subsequences ofdiagrams in the correlation correction are summarized: screening of the residual electronelectron interaction, particle-hole interaction, and the iterations of the self-energy.
It is shown that the Hartree-Fock method provides the exact fulfilment of the Schiff theorem (ext... more It is shown that the Hartree-Fock method provides the exact fulfilment of the Schiff theorem (external electric field shielding at the nucleus). The numerical calculation of the electric field in the Tl+ ion was carried out. The shielded field E
The 7.6 eV electromagnetic transition between the nearly degenerate ground state and first excite... more The 7.6 eV electromagnetic transition between the nearly degenerate ground state and first excited state in the 229 Th nucleus may be very sensitive to potential changes in the fine-structure constant, α = e 2 /hc. However, the sensitivity is not known, and nuclear calculations are currently unable to determine it. We propose measurements of the differences of atomic transition frequencies between thorium atoms (or ions) with the nucleus in the ground state and in the first excited (isomeric) state. This will enable extraction of the change in nuclear charge radius and electric quadrupole moment between the isomers, and hence the α-dependence of the isomeric transition frequency with reasonable accuracy.
We consider microwave hyperfine transitions in the ground state of cesium and rubidium atoms whic... more We consider microwave hyperfine transitions in the ground state of cesium and rubidium atoms which are presently used as the primary and the secondary frequency standards. The atoms are confined in an optical lattice generated by a circularly polarized laser field. We demonstrate that applying an external magnetic field with appropriately chosen direction may cancel dynamic Stark frequency shift making the frequency of the clock transition insensitive to the strengths of both the laser and the magnetic fields. This can be attained for practically any laser frequency which is sufficiently distant from a resonance.
We have performed ab initio calculations of the frequency shift induced by a static electric fiel... more We have performed ab initio calculations of the frequency shift induced by a static electric field on the cesium clock hyperfine transition. The calculations are used to find the frequency shifts due to blackbody radiation. Our result (δν/E 2 = −2.26(2) × 10 −10 Hz/(V/m) 2) is in good agreement with early measurements and ab initio calculations performed in other groups. We present arguments against recent claims that the actual value of the effect might be smaller. The difference (∼ 10%) between ab initio and semiempirical calculations is due to the contribution of the continuum spectrum to the sum over intermediate states.
We explore a feasibility of measuring atom-wall interaction using atomic clocks based on atoms tr... more We explore a feasibility of measuring atom-wall interaction using atomic clocks based on atoms trapped in engineered optical lattices. Optical lattice is normal to the wall. By monitoring the wall-induced clock shift at individual wells of the lattice, one would measure a dependence of the atom-wall interaction on the atom-wall separation. We rigorously evaluate the relevant clock shifts and show that the proposed scheme may uniquely probe the long-range atom-wall interaction in all three qualitatively-distinct regimes of the interaction: van der Waals (image-charge interaction), Casimir-Polder (QED vacuum fluctuations) and Lifshitz (thermal bath fluctuations). The analysis is carried out for atoms Mg, Ca, Sr, Cd, Zn, and Hg, with a particular emphasis on Sr clock.
We propose a new class of atomic microwave clocks based on the hyperfine transitions in the groun... more We propose a new class of atomic microwave clocks based on the hyperfine transitions in the ground state of aluminum or gallium atoms trapped in optical lattices. For these elements magic wavelengths exist at which both levels of the hyperfine doublet are shifted at the same rate by the lattice laser field, cancelling its effect on the clock transition. Our analysis of various systematic effects shows that, while offering an improved control over systematic errors, the accuracy of the proposed microwave clock is competitive to that of the state-of-the-art primary frequency standard.
We have calculated the 6s − 7s parity nonconserving (PNC) E1 transition amplitude, E P N C , in c... more We have calculated the 6s − 7s parity nonconserving (PNC) E1 transition amplitude, E P N C , in cesium. We have used an improved all-order technique in the calculation of the correlations and have included all significant contributions to E P N C. Our final value E P N C = 0.904 1 ± 0.5% × 10 −11 iea B (−Q W /N) has half the uncertainty claimed in old calculations used for the interpretation of Cs PNC experiments. The resulting nuclear weak charge Q W for Cs deviates by about 2σ from the value predicted by the standard model.
The contribution of core nucleons to a static magnetic quadrupole moment is calculated in the pre... more The contribution of core nucleons to a static magnetic quadrupole moment is calculated in the presence of an interaction that violates P and T invariance. The contribution found can be comparable or even larger than the contribution of a valence nucleon, in contrast to the case of the P-violating but T-invariant anapole moment. The core contribution appears to be sensitive to the spin-orbit single-particle potential, which enhances it by a factor of ϳ2. ͓S0556-2813͑96͒04711-5͔
A relativistic method for the calculation of positron binding to atoms is presented. The method c... more A relativistic method for the calculation of positron binding to atoms is presented. The method combines a configuration-interaction treatment of the valence electron and the positron, with a many-body perturbationtheory description of their interaction with the atomic core. We apply this method to positron binding by the copper atom and obtain a binding energy of 170 meV (Ϯ10%). To check the accuracy of the method we use a similar approach to calculate the negative copper ion. The calculated electron affinity is 1.218 eV, in good agreement with the experimental value of 1.236 eV. The problem of convergence of positron-atom bound-state calculations is investigated, and means to improve it are discussed. The relativistic character of the method and its satisfactory convergence make it a suitable tool for heavier atoms. ͓S1050-2947͑99͒08311-0͔
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