Enhancement factor for the electron electric dipole moment in francium and gold atoms

If electrons had an electric dipole moment (EDM) they would induce EDMs of atoms. The ratio of the atomic EDM to the electron EDM for a particular atom is called the enhancement factor, R. We calculate the enhancement factor for the francium and gold atoms, with the results 910 plus/minus 5% for Fr and 260 plus/minus 15% for Au. The large values of these enhancement factors make these atoms attractive for electron EDM measurements, and hence the search for time-reversal invariance violation.Comment: 6 pages, no figures, uses RevTex, reference adde

Off-Diagonal Hyperfine Interaction and Parity Non-conservation in Cesium

We have performed relativistic many-body calculations of the hyperfine interaction in the $6s$ and $7s$ states of Cs, including the off-diagonal matrix element. The calculations were used to determine the accuracy of the semi-empirical formula for the electromagnetic transition amplitude $$ induced by the hyperfine interaction. We have found that even though the contribution of the many-body effects into the matrix elements is very large, the square root formula $= \sqrt{ }$ remains valid to the accuracy of a fraction of $10^{-3}$. The result for the M1-amplitude is used in the interpretation of the parity-violation measurement in the $6s-7s$ transition in Cs which claims a possible deviation from the Standard model.Comment: 13 pages, 4 figures, LaTeX, Submitted to Phys. Rev.

Musical recommendations and personalization in a social network

This paper presents a set of algorithms used for music recommendations and personalization in a general purpose social network www.ok.ru, the second largest social network in the CIS visited by more then 40 millions users per day. In addition to classical recommendation features like "recommend a sequence" and "find similar items" the paper describes novel algorithms for construction of context aware recommendations, personalization of the service, handling of the cold-start problem, and more. All algorithms described in the paper are working on-line and are able to detect and address changes in the user's behavior and needs in the real time. The core component of the algorithms is a taste graph containing information about different entities (users, tracks, artists, etc.) and relations between them (for example, user A likes song B with certainty X, track B created by artist C, artist C is similar to artist D with certainty Y and so on). Using the graph it is possible to select tracks a user would most probably like, to arrange them in a way that they match each other well, to estimate which items from a fixed list are most relevant for the user, and more. In addition, the paper describes the approach used to estimate algorithms efficiency and analyze the impact of different recommendation related features on the users' behavior and overall activity at the service.Comment: This is a full version of a 4 pages article published at ACM RecSys 201

Energy levels and lifetimes of Nd IV, Pm IV, Sm IV, and Eu IV

To address the shortage of experimental data for electron spectra of triply-ionized rare earth elements we have calculated energy levels and lifetimes of 4f{n+1} and 4f{n}5d configurations of Nd IV (n=2), Pm IV (n=3), Sm IV (n=4), and Eu IV (n=5) using Hartree-Fock and configuration interaction methods. To control the accuracy of our calculations we also performed similar calculations for Pr III, Nd III and Sm III, for which experimental data are available. The results are important, in particular, for physics of magnetic garnets.Comment: 4 pages 1 tabl

Relativistic effects in Ni II and the search for variation of the fine structure constant

Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical ``constants'' in the Universe. Detection of high redshift absorption systems intersecting the sight lines towards distant quasars provide a powerful tool for measuring these variations. In the present paper we demonstrate that high sensitivity to variation of the fine structure constant alpha can be obtained by comparing cosmic and laboratory spectra of the Ni II ion. Relativistic effects in Ni II reveal many interesting features. The Ni II spectrum exhibits avoided level crossing phenomenon under variation of alpha and the intervals between the levels have strong nonlinear dependencies on relativistic corrections. The values of the transition frequency shifts, due to the change of alpha, vary significantly from state to state including change of the sign. This enhances the sensitivity to the variation of alpha and reduces possible systematic errors. The calculations of alpha-dependence of the nickel ion spectral lines that are detectable in quasar absorption spectra have been performed using a relativistic configuration interaction method.Comment: 13 pages, 1 figure, accepted by Phys. Rev. A, typos corrected, acknowledgment adde

On the use of the VN−MV^{N-M} approximation in atomic calculations

We demonstrate that $V^{N-M}$ approximation is a good starting point for the configuration interaction calculations for many-electron atoms and ions. $N$ is the total number of electrons in the neutral atom, $M$ is the number of valence electrons. $V^{N-M}$ is the self-consistent Hartree Fock potential for a closed-shell ion with all valence electrons removed. Using of the $V^{N-M}$ approximation considerably simplifies the many-body perturbation theory for the core-valence correlations. It makes it easier to include higher-order correlations which often significantly improves the accuracy of the calculations. Calculations for krypton and barium and their positive ions are presented for illustration.Comment: 5 pages,1 figure, submitted to Phys. Rev.