Tag Archives: Atomic Physics

Searching for axion stars and Q-balls with a terrestrial magnetometer network [CL]

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http://arxiv.org/abs/1710.04323


Light (pseudo-)scalar fields are promising candidates to be the dark matter in the Universe. Under certain initial conditions in the early Universe and/or with certain types of self-interactions, they can form compact dark-matter objects such as axion stars or Q-balls. Direct encounters with such objects can be searched for by using a global network of atomic magnetometers. It is shown that for a range of masses and radii not ruled out by existing observations, the terrestrial encounter rate with axion stars or Q-balls can be sufficiently high (at least once per year) for a detection. Furthermore, it is shown that a global network of atomic magnetometers is sufficiently sensitive to pseudoscalar couplings to atomic spins so that a transit through an ALP star or Q-ball could be detected over a broad range of unexplored parameter space.

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D. Kimball, D. Budker, J. Eby, et. al.
Fri, 13 Oct 17
33/56

Comments: 8 pages, 3 figures

Resonant Electron Impact Excitation of 3d levels in Fe$^{14+}$ and Fe$^{15+}$ [SSA]

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http://arxiv.org/abs/1710.03548


We present laboratory spectra of the $3p$–$3d$ transitions in Fe$^{14+}$ and Fe$^{15+}$ excited with a mono-energetic electron beam. In the energy dependent spectra obtained by sweeping the electron energy, resonant excitation is confirmed as an intensity enhancement at specific electron energies. The experimental results are compared with theoretical cross sections calculated based on fully relativistic wave functions and the distorted-wave approximation. Comparisons between the experimental and theoretical results show good agreement for the resonance strength. A significant discrepancy is, however, found for the non-resonant cross section in Fe$^{14+}$, which can be considered as a fundamental cause of the line intensity ratio problem that has often been found in both observatory and laboratory measurements.

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T. Tsuda, E. Shimizu, S. Ali, et. al.
Wed, 11 Oct 17
3/65

Comments: N/A

Localizing Gravitational Wave Sources with Single-Baseline Atom Interferometers [CL]

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http://arxiv.org/abs/1710.03269


Localizing sources on the sky is crucial for realizing the full potential of gravitational waves for astronomy, astrophysics, and cosmology. We show that the mid-frequency band, roughly 0.03 to 10 Hz, has significant potential for angular localization. The angular location is measured through the changing Doppler shift as the detector orbits the Sun. This band maximizes the effect since these are the highest frequencies in which sources live several months. Atom interferometer detectors can observe in the mid-frequency band, and even with just a single baseline can exploit this effect for sensitive angular localization. The single baseline orbits around the Earth and the Sun, causing it to reorient and change position significantly during the lifetime of the source, and making it similar to having multiple baselines/detectors. For example, atomic detectors could predict the location of upcoming black hole or neutron star merger events with sufficient accuracy to allow optical and other electromagnetic telescopes to observe these events simultaneously. Thus, mid-band atomic detectors are complementary to other gravitational wave detectors and will help complete the observation of a broad range of the gravitational spectrum.

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P. Graham and S. Jung
Wed, 11 Oct 17
30/65

Comments: 16 pages, 3 figures, 2 tables

Near L-Edge Single and Multiple Photoionization of Singly Charged Iron Ions [IMA]

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http://arxiv.org/abs/1709.09092


Absolute cross sections for m-fold photoionization (m=1,…,6) of Fe+ by a single photon were measured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source, operated by DESY in Hamburg, Germany. Photon energies were in the range 680-920 eV which covers the photoionization resonances associated with 2p and 2s excitation to higher atomic shells as well as the thresholds for 2p and 2s ionization. The corresponding resonance positions were measured with an uncertainty of +- 0.2 eV. The cross section for Fe+ photoabsorption is derived as the sum of the individually measured cross-sections for m-fold ionization. Calculations of the Fe+ absorption cross sections have been carried out using two different theoretical approaches, Hartree-Fock including relativistic extensions and fully relativistic Multi-Configuration Dirac Fock. Apart from overall energy shifts of up to about 3 eV, the theoretical cross sections are in good agreement with each other and with the experimental results. In addition, the complex deexcitation cascades after the creation of inner-shell holes in the Fe+ ion have been tracked on the atomic fine-structure level. The corresponding theoretical results for the product charge-state distributions are in much better agreement with the experimental data than previously published configuration-average results. The present experimental and theoretical results are valuable for opacity calculations and are expected to pave the way to a more accurate determination of the iron abundance in the interstellar medium.

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S. Schippers, M. Martins, R. Beerwerth, et. al.
Wed, 27 Sep 2017
1/81

Comments: 18 pages, 10 figures, 4 tables, accepted for publication in The Astrophysical Journal

Spin Precession Experiments for Light Axionic Dark Matter [CL]

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http://arxiv.org/abs/1709.07852


Axion-like particles are promising candidates to make up the dark matter of the universe, but it is challenging to design experiments that can detect them over their entire allowed mass range. Dark matter in general, and in particular axion-like particles and hidden photons, can be as light as roughly $10^{-22} \;\rm{eV}$ ($\sim 10^{-8} \;\rm{Hz}$), with astrophysical anomalies providing motivation for the lightest masses (“fuzzy dark matter”). We propose experimental techniques for direct detection of axion-like dark matter in the mass range from roughly $10^{-13} \;\rm{eV}$ ($\sim 10^2 \;\rm{Hz}$) down to the lowest possible masses. In this range, these axion-like particles act as a time-oscillating magnetic field coupling only to spin, inducing effects such as a time-oscillating torque and periodic variations in the spin-precession frequency with the frequency and direction set by fundamental physics. We show how these signals can be measured using existing experimental technology, including torsion pendulums, atomic magnetometers, and atom interferometry. These experiments demonstrate a strong discovery capability, with future iterations of these experiments capable of pushing several orders of magnitude past current astrophysical bounds.

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P. Graham, D. Kaplan, J. Mardon, et. al.
Mon, 25 Sep 2017
12/60

Comments: 18 pages, 4 figures

High-resolution one-photon absorption spectroscopy of the $D\,{}^2Σ^- \leftarrow X\,{}^2Π$ system of radical OH and OD [CL]

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http://arxiv.org/abs/1709.02509


Vacuum-ultraviolet (VUV) photoabsorption spectra were recorded of the $A\,{}^2\Sigma^+(v’=0)\leftarrow{}X\,{}^2\Pi(v”=0)$, $D\,{}^2\Sigma^-(v’=0)\leftarrow{}X\,{}^2\Pi(v”=0)$ and $D\,{}^2\Sigma^-(v’=1)\leftarrow{}X\,{}^2\Pi(v”=0)$ bands of the OH and OD radicals generated in a plasma-discharge source using synchrotron radiation as a background continuum coupled with the VUV Fourier-transform spectrometer on the DESIRS beamline of synchrotron SOLEIL. High-resolution spectra permitted the quantification of transition frequencies, relative $f$-values, and natural line broadening. The $f$-values were absolutely calibrated with respect to a previous measurement of $A\,{}^2\Sigma^+(v’=0)\leftarrow{}X\,{}^2\Pi(v”=0)$ ([wang1979]). Lifetime broadening of the excited $D\,{}^2\Sigma^-(v=0)$ and $D\,{}^2\Sigma^-(v=1)$ levels is measured for the first time and compared with previous experimental limits, and implies a lifetime 5 times shorter than a theoretical prediction ([van_der_loo2005]). A local perturbation of the $D\,{}^2\Sigma^-(v=0)$ level in OH was found.

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A. Heays, N. Oliveira, B. Gans, et. al.
Mon, 11 Sep 17
19/49

Comments: N/A

Isotope shift, non-linearity of King plot and search for nuclear island of stability and new particles [CL]

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http://arxiv.org/abs/1709.00600


The Racah-Rosenthal-Breit formula describes the isotope field shift for s-wave only and is not valid in heavy atoms where the relativistic effects are important. We derive a single-particle relativistic formula for the isotope shift for an arbitrary electron angular momentum; we then apply it to estimate the differences in the transition frequencies between the superheavy atoms produced in laboratory and atoms with nuclei belonging to the hypothetical island of stability (these nuclei have a “magical” number of neutrons N=184). Our results may be applied to the search for metastable neutron-rich isotopes in astrophysical atomic spectra using the known values of the transition frequencies for the neutron deficient isotopes produced in laboratory. An example may be the spectra of the Przybylski’s star where superheavy elements up to Z=99 have been possibly identified.
We have found that the nuclear polarizability contribution leads to the significant deviation of the King plot for isotope shifts from the linearity. Therefore, the measurements of the non-linearity of King plots may be applied to measure the nuclear polarizability change between individual isotopes. It was recently suggested that such measurements may also be used to search for new particles mediating Yukawa-type interactions in atoms. We estimate the non-linear corrections to the King plot including contributions of the relativistic effects in the field shift, isotope shift due to the nuclear polarizability, many-body effects and effect of hypothetical new particles. Our estimates provide theoretical limitations on the sensitivity of such a search and should help in selection of the most suitable atoms for corresponding experiments.

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V. Flambaum, A. Geddes and A. Viatkina
Tue, 5 Sep 17
23/76

Comments: N/A

Search for axion-like dark matter through nuclear spin precession in electric and magnetic fields [CL]

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http://arxiv.org/abs/1708.06367


We report on a search for ultra-low-mass axion-like dark matter by analysing the ratio of the spin-precession frequencies of stored ultracold neutrons and $^{199}$Hg atoms for an axion-induced oscillating electric dipole moment of the neutron and an axion-wind spin-precession effect. No signal consistent with dark matter is observed for the axion mass range $10^{-24}~\textrm{eV} \le m_a \le 10^{-17}~\textrm{eV}$. Our null result sets the first laboratory constraints on the coupling of axion dark matter to gluons, which improve on astrophysical limits by up to 3 orders of magnitude, and also improves on previous laboratory constraints on the axion coupling to nucleons by up to a factor of 40.

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C. Abel, N. Ayres, G. Ban, et. al.
Wed, 23 Aug 17
36/45

Comments: N/A

Electron-Impact Multiple Ionization Cross Sections for Atoms and Ions of Helium through Zinc [IMA]

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http://arxiv.org/abs/1708.02155


We have compiled a set of electron-impact multiple ionization (EIMI) cross sections for astrophysically relevant ions. EIMI can have a significant effect on the ionization balance of non-equilibrium plasmas. For example, it can be important if there is a rapid change in the electron temperature or if there is a non-thermal electron energy distribution, such as a kappa distribution. Cross sections for EIMI are needed in order to account for these processes in plasma modeling and for spectroscopic interpretation. Here, we describe our comparison of proposed semiempirical formulae to the available experimental EIMI cross section data. Based on this comparison, we have interpolated and extrapolated fitting parameters to systems that have not yet been measured. A tabulation of the fit parameters is provided for 3466 EIMI cross sections. We also highlight some outstanding issues that remain to be resolved.

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M. Hahn, A. Mueller and D. Savin
Tue, 8 Aug 17
23/65

Comments: Submitted to Astrophysical Journal Supplement. The cross section database (Table 2 in the manuscript) is available upon request

Editorial: Special Issue on the Atomic and Molecular Processes in the Ultracold Regime, the Chemical Regime, and Astrophysics [CL]

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http://arxiv.org/abs/1708.00943


This editorial introduces the J. Phys. B: Atomic, Molecular and Optical Physics Special Issue “Atomic and Molecular Processes in the Ultracold Regime, the Chemical Regime and Astrophysics” dedicated to Professor Alexander Dalgarno (1928-2015). After a brief biographical review, short summaries of the contributed papers and their relations to some of Prof. Dalgarno’s work are given.

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J. Babb, R. Cote, H. Sadeghpour, et. al.
Fri, 4 Aug 17
27/47

Comments: 7 pp

On the treatment of $\ell$-changing proton-hydrogen Rydberg atom collisions [CL]

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http://arxiv.org/abs/1707.09256


Energy-conserving, angular momentum-changing collisions between protons and highly excited Rydberg hydrogen atoms are important for precise understanding of atomic recombination at the photon decoupling era, and the elemental abundance after primordial nucleosynthesis. Early approaches to $\ell$-changing collisions used perturbation theory for only dipole-allowed ($\Delta \ell=\pm 1$) transitions. An exact non-perturbative quantum mechanical treatment is possible, but it comes at computational cost for highly excited Rydberg states. In this note we show how to obtain a semi-classical limit that is accurate and simple, and develop further physical insights afforded by the non-perturbative quantum mechanical treatment.

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D. Vrinceanu, R. Onofrio and H. Sadeghpour
Tue, 1 Aug 17
13/55

Comments: N/A

Application of Relativistic Coupled-cluster Theory to Electron Impact Excitations of Mg$^+$ in the Plasma Environment [CL]

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http://arxiv.org/abs/1707.02935


A relativistic coupled-cluster (RCC) theory is implemented to study electron impact excitations of atomic species. As a test case, the electron impact excitations of the $3s ~ ^2S_{1/2} – 3p ~ ^2P_{1/2;3/2}$ resonance transitions are investigated in the singly charged magnesium (Mg$^+$) ion using this theory. Accuracies of wave functions of Mg$^+$ are justified by evaluating its attachment energies of the relevant states and compared with the experimental values. The continuum wave function of the projectile electron are obtained by solving Dirac equations assuming distortion potential as static potential of the ground state of Mg$^+$. Comparison of the calculated electron impact excitation differential and total cross-sections with the available measurements are found to be in very good agreements at various incident electron energies. Further, calculations are carried out in the plasma environment in the Debye H\”uckel model framework, which could be useful in the astrophysics. Influence of plasma strength on the cross-sections as well as linear polarization of the photon emission in the $3p ~ ^2P_{3/2} – 3s ~ ^2S_{1/2}$ transition is investigated for different incident electron energies.

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L. Sharma, B. Sahoo, P. Malkar, et. al.
Tue, 11 Jul 17
61/74

Comments: 9 pages, 1 table and 3 figures

Rate constants for the formation of SiO by radiative association [IMA]

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http://arxiv.org/abs/1707.01864


Accurate molecular data for the low-lying states of SiO are computed and used to calculate rate constants for radiative association of Si and O. Einstein A-coefficients are also calculated for transitions between all of the bound and quasi-bound levels for each molecular state. The radiative widths are used together with elastic tunneling widths to define effective radiative association rate constants which include both direct and indirect (inverse predissociation) formation processes. The indirect process is evaluated for two kinetic models which represent limiting cases for astrophysical environments. The first case scenario assumes an equilibrium distribution of quasi-bound states and would be applicable whenever collisional and/or radiative excitation mechanisms are able to maintain the population. The second case scenario assumes that no excitation mechanisms are available which corresponds to the limit of zero radiation temperature and zero atomic density. Rate constants for SiO formation in realistic astrophysical environments would presumably lie between these two limiting cases.

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M. Cairnie, R. Forrey, J. Babb, et. al.
Fri, 7 Jul 17
15/46

Comments: To appear in MNRAS

Cyclotron transitions of bound ions [CL]

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http://arxiv.org/abs/1706.06561


A charged particle in a magnetic field possesses discrete energy levels associated with particle’s rotation around the field lines. The radiative transitions between these levels are the well-known cyclotron transitions. We show that a bound complex of particles with a non-zero net charge displays analogous transitions between the states of confined motion of the entire complex in the field. The latter {\em bound-ion cyclotron transitions} are affected by a coupling between the collective and internal motions of the complex and, as a result, differ from the transitions of a “reference” bare ion with the same mass and charge. We analyze the cyclotron transitions for complex ions by including the coupling within a rigorous quantum approach. Particular attention is paid to comparison of the transition energies and oscillator strengths to those of the bare ion. Selection rules based on integrals of collective motion are derived for the bound-ion cyclotron transitions analytically, and the perturbation and coupled-channel approaches are developed to study the transitions quantitatively. Representative examples are considered and discussed for positive and negative atomic and cluster ions.

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V. Bezchastnov and G. Pavlov
Wed, 21 Jun 17
29/64

Comments: 20 pages, including 3 figures. Submitted to PRA

Inelastic e+Mg collision data and its impact on modelling stellar and supernova spectra [IMA]

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http://arxiv.org/abs/1706.03399


Results of calculations for inelastic e+Mg effective collision strengths for the lowest 25 physical states of Mg I (up to 3s6p 1P), and thus 300 transitions, from the convergent close-coupling (CCC) and the B-spline R-matrix (BSR) methods are presented. At temperatures of interest, ~5000 K, the results of the two calculations differ on average by only 4%, with a scatter of 27%. As the methods are independent, this suggests that the calculations provide datasets for e+Mg collisions accurate to this level. Comparison with the commonly used dataset compiled by Mauas et al. (1988), covering 25 transitions among 12 states, suggests the Mauas et al. data are on average ~57% too low, and with a very large scatter of a factor of ~6.5. In particular the collision strength for the transition corresponding to the Mg I intercombination line at 457 nm is significantly underestimated by Mauas et al., which has consequences for models that employ this dataset. In giant stars the new data leads to a stronger line compared to previous non-LTE calculations, and thus a reduction in the non-LTE abundance correction by ~0.1 dex (~25%). A non-LTE calculation in a supernova ejecta model shows this line becomes significantly stronger, by a factor of around two, alleviating the discrepancy where the 457 nm line in typical models with Mg/O ratios close to solar tended to be too weak compared to observations.

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P. Barklem, Y. Osorio, D. Fursa, et. al.
Tue, 13 Jun 17
8/92

Comments: Accepted for publication in Astronomy and Astrophysics

Decoherence in excited atoms by low-energy scattering [CL]

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http://arxiv.org/abs/1706.03077


We describe a new mechanism of decoherence in excited atoms as a result of thermal particles scattering by the atomic nucleus. It is based on the idea that a single scattering will produce a sudden displacement of the nucleus, which will be perceived by the electron in the atom as an instant shift in the electrostatic potential. This will leave the atom’s wave-function partially projected into lower-energy states which will lead to decoherence of the atomic state. The decoherence is calculated to increase with the excitation of the atom, making observation of the effect easier in Rydberg atoms. We estimate the order of the decoherence for photons and massive particles scattering, analyzing several commonly presented scenarios. Our scheme can be applied to the detection of weakly-interacting particles, like those which may be the constituents of Dark Matter, which interaction was calculated to have a more prominent effect that the background radiation.

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D. Quinones and B. Varcoe
Tue, 13 Jun 17
35/92

Comments: N/A

Extracting dark matter signatures from atomic clock stability measurements [CL]

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http://arxiv.org/abs/1705.05833


We analyze possible effects of the dark matter environment on the atomic clock stability measurements. The dark matter is assumed to exist in a form of waves of ultralight scalar fields or in a form of topological defects (monopoles and strings). We identify dark matter signal signatures in clock Allan deviation plots that can be used to constrain the dark matter coupling to the Standard Model fields. The existing data on the Al+/Hg+ clock comparison are used to put new limits on the dilaton dark matter in the region of masses m > 10^{-15} eV. We also estimate the sensitivities of future atomic clock experiments in space, including the cesium microwave and strontium optical clocks aboard the International Space Station, as well as a potential nuclear clock. These experiments are expected to put new limits on the topological dark matter in the range of masses 10^{-10} eV < m < 10^{-6} eV.

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T. Kalaydzhyan and N. Yu
Thu, 18 May 17
37/60

Comments: 13 pages, 5 figures. Comments are welcome

Thermodynamically-consistent semi-classical $\ell$-changing rates [CL]

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http://arxiv.org/abs/1704.08722


We compare the results of the semi-classical (SC) and quantum-mechanical (QM) formalisms for angular-momentum changing transitions in Rydberg atom collisions given by Vrinceanu & Flannery, J. Phys. B 34, L1 (2001), and Vrinceanu, Onofrio & Sadeghpour, ApJ 747, 56 (2012), with those of the SC formalism using a modified Monte Carlo realization. We find that this revised SC formalism agrees well with the QM results. This provides further evidence that the rates derived from the QM treatment are appropriate to be used when modelling recombination through Rydberg cascades, an important process in understanding the state of material in the early universe. The rates for $\Delta\ell=\pm1$ derived from the QM formalism diverge when integrated to sufficiently large impact parameter, $b$. Further to the empirical limits to the $b$ integration suggested by Pengelly & Seaton, MNRAS 127, 165 (1964), we suggest that the fundamental issue causing this divergence in the theory is that it does not fully cater for the finite time taken for such distant collisions to complete.

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R. Williams, F. Guzman, N. Badnell, et. al.
Mon, 1 May 17
19/46

Comments: 12 pages, 4 figures. To be published in J Phys B. Author original version: journal accepted version, with minor changes, will be posted after embargo period

Radiative rates and electron impact excitation rates for transitions in He II [SSA]

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http://arxiv.org/abs/1704.07275


We report calculations of energy levels, radiative rates, collision strengths, and effective collision strengths for transitions among the lowest 25 levels of the n <= 5 configurations of He~II. The general-purpose relativistic atomic structure package (GRASP) and Dirac atomic R-matrix code (DARC) are adopted for the calculations. Radiative rates, oscillator strengths, and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among the 25 levels. Furthermore, collision strengths and effective collision strengths are listed for all 300 transitions among the above 25 levels over a wide energy (temperature) range up to 9 Ryd (10**5.4 K). Comparisons are made with earlier available results and the accuracy of the data is assessed.

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K. Aggarwal, A. Igarashi, F. Keenan, et. al.
Tue, 25 Apr 17
2/59

Comments: 30 pages of text including 12 figures and 5 Tables will appear in ATOMS 5 (2017)

GPS as a dark matter detector: Orders-of-magnitude improvement on couplings of clumpy dark matter to atomic clocks [CL]

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http://arxiv.org/abs/1704.06844


Multiple cosmological observations indicate that dark matter (DM) constitutes 85% of all matter in the Universe [1]. All the current evidence for DM comes from galactic or larger scale observations through the gravitational pull of DM on ordinary matter [1], leaving the microscopic nature of DM a mystery. Ambitious programs in particle physics have mostly focused on searches for WIMPs (Weakly Interacting Massive Particles) as DM candidates [2]. As WIMPs remain elusive, there is a growing interest in alternatives. Some models [3-7] predict DM in the form of spatially large objects (“clumps”) that may cause glitches in atomic clocks [6]. Here we use the network of atomic clocks on board the GPS satellites as a 50,000 km aperture detector to search for DM clumps. As DM clumps sweep through the GPS satellite constellation at galactic velocities ~300 km/s, their predicted signature is a correlated propagation of clock glitches through the constellation over a period of a few minutes [6]. By mining 16 years of archival GPS data, we find no evidence for DM clumps in the form of domain walls. This enables us to improve limits on DM couplings to atomic clocks by several orders of magnitude. Our work demonstrates the use of a global network of precision measurement devices in the search for DM. Several global networks including magnetometers, laboratory atomic clocks, and other precision devices are being developed [5,8,9]. We anticipate that our methods will be valuable for probing new physics in this emerging area.

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B. Roberts, G. Blewitt, C. Dailey, et. al.
Tue, 25 Apr 17
20/59

Comments: N/A

Reproduction of Interstellar Infrared Spectrum of Reflection Nebula NGC2023 By A Hydrocarbon Pentagon-Hexagon Combined Molecule [CL]

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http://arxiv.org/abs/1704.06197


Reflection Nebula NGC2023 shows specific interstellar infrared spectrum due to polycyclic aromatic hydrocarbon (PAH) in a wide wavelength range from 5 to 20 micrometer. By our previous quantum chemistry calculation, it was suggested that a molecule group having hydrocarbon pentagon-hexagon combined skeleton could reproduce ubiquitous interstellar infrared spectrum. In this paper, observed NGC2023 spectrum was compared in detail with such carrier candidates. First model molecule was di-cation (C23H12)2+ with two hydrocarbon pentagons combined with five hexagons. Observed strong infrared bands were 6.2, 7.7, 8.6, and 11.2 micrometer. Whereas, calculated strong peaks were 6.4, 7.5, 7.7, 8.5, and 11.2 micrometer. Observed weaker bands from 10 to 15 micrometer were 11.0, 12.0, 12.7, 13.5, and 14.2 micrometer, which were reproduced well by computed bands as 10.9, 12.0, 12.6, 13.6, and 14.0 micrometer. From 15 to 20 micrometer, observed 15.8, 16.4, 17.4, 17.8, and 19.0 micrometer were correlated with calculated 15.6, 16.5, 17.2, 18.2, and 18.8 micrometer. It should be noted that we could successfully reproduce interstellar infrared spectrum by applying a single molecule. Second model molecule was (C12H8)3+ with one pentagon combined with two hexagons. Again, observed strong bands at 6.2, 7.7, 8.6, 11.2 and 12.7 micrometer were successfully computed as 6.3, 7.4, 7.7, 8.6, 11.1, and 12.8 micrometer. It was concluded that by introducing hydrocarbon pentagon-hexagon combined ionized molecules, interstellar PAH oriented infrared spectrum could be successfully reproduced.

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N. Ota
Fri, 21 Apr 17
32/73

Comments: 6 pages, 3 figures, 1 table

Identification of Near-Infrared [Se III] and [Kr VI] Emission Lines in Planetary Nebulae [SSA]

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http://arxiv.org/abs/1704.00741


We identify [Se III] 1.0994 micron in the planetary nebula (PN) NGC 5315 and [Kr VI] 1.2330 micron in three PNe, from spectra obtained with the FIRE spectrometer on the 6.5-m Baade Telescope. Se and Kr are the two most widely-detected neutron-capture elements in astrophysical nebulae, and can be enriched by s-process nucleosynthesis in PN progenitor stars. The detection of [Se III] 1.0994 micron is particularly valuable when paired with observations of [Se IV] 2.2858 micron, as it can be used to improve the accuracy of nebular Se abundance determinations, and allows Se ionization correction factor (ICF) schemes to be empirically tested for the first time. We present new effective collision strength calculations for Se^{2+} and Kr^{5+}, which we use to compute ionic abundances. In NGC 5315, we find that the Se abundance computed from Se^{3+}/H^+ is lower than that determined with ICFs that incorporate Se^{2+}/H^+. We compute new Kr ICFs that take Kr^{5+}/H^+ into account, by fitting correlations found in grids of Cloudy models between Kr ionic fractions and those of more abundant elements, and use these to derive Kr abundances in four PNe. Observations of [Se III] and [Kr VI] in a larger sample of PNe, with a range of excitation levels, are needed to rigorously test the ICF prescriptions for Se and our new Kr ICFs.

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N. Sterling, S. Madonna, K. Butler, et. al.
Wed, 5 Apr 17
44/45

Comments: 18 pages, 4 figures, accepted for publication in ApJ

Recombination coefficients for O II lines in nebular conditions [CL]

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http://arxiv.org/abs/1703.09982


We present the results of a calculation of recombination coefficients for O^{2+} + e^- using an intermediate coupling treatment that fully accounts for the dependence of the distribution of population among the ground levels of O^{2+} on electron density and temperature. The calculation is extended down to low electron temperatures where dielectronic recombination arising from Rydberg states converging on the O^{2+} ground levels is an important process. The data, which consist of emission coefficients for 8889 recombination lines and recombination coefficients for the ground and metastable states of O^+ are in Cases A, B and C, and are organised as a function of the electron temperature and number density, as well as wavelength. An interactive fortran 77 data server is also provided as an accessory for mining the line emission coefficients and obtaining Lagrange interpolated values for any choice of the two variables between the explicitly provided values for any set of wavelengths. Some illustrations of the application of the new data to nebular observations are also provided.

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P. Storey, T. Sochi and R. Bastin
Thu, 30 Mar 17
37/69

Comments: 14 pages, 7 figures, 6 tables

Fibre-optic delivery of time and frequency to VLBI station [IMA]

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http://arxiv.org/abs/1703.09479


The quality of Very Long Baseline Interferometry (VLBI) radio observations predominantly relies on precise and ultra-stable time and frequency (T&F) standards, usually hydrogen masers (HM), maintained locally at each VLBI station. Here, we present an operational solution in which the VLBI observations are routinely carried out without use of a local HM, but using remote synchronization via a stabilized, long-distance fibre-optic link. The T&F reference signals, traceable to international atomic timescale (TAI), are delivered to the VLBI station from a dedicated timekeeping laboratory. Moreover, we describe a proof-of-concept experiment where the VLBI station is synchronized to a remote strontium optical lattice clock during the observation.

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P. Krehlik, L. Buczek, J. Kolodziej, et. al.
Wed, 29 Mar 17
21/63

Comments: 8 pages, 8 figures, accepted for publication in A&A, section Astronomical instrumentation

Isotope shift and search for metastable superheavy elements in astrophysical data [CL]

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http://arxiv.org/abs/1703.04250


Spectral lines belonging to the short-lifetime heavy radioactive elements up to Es ($Z$=99) have been found in the spectra of the Przybylski’s star. We suggest that these unstable elements may be decay products of a “magic” metastable nucleus belonging to the the island of stability where the nuclei have a magic number of neutrons $N=184$. The laboratory-produced nuclei have a significantly smaller number of neutrons. To identify spectra of the $N=184$ isotopes of these nuclei and their neutron-reach superheavy decay products in astrophysical data we calculate the isotope shift which should be added to the laboratory – measured wavelenghs. The results for the isotopic shifts in the strongest optical electromagnetic transitions in No, Lr, Nh, Fl,and $Z$=120 elements are presented.

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V. Dzuba, V. Flambaum and J. Webb
Tue, 14 Mar 17
16/74

Comments: 4 pages, no figures

Charge exchange in the ultraviolet: implication for interacting clouds in the core of NGC 1275 [GA]

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http://arxiv.org/abs/1703.01151


Charge exchange emission is known to provide a key diagnostic to the interface between hot and cold matter in many astrophysical environments. Most of the recent charge exchange studies focus on its emission in the X-ray band, but few on the UV part, although the latter can also provide a powerful probe of the charge exchange process. An atomic calculation, as well as an application to observed data, are presented to explore and describe the potential use of the UV data for the study of cosmic charge exchange. Using the newest charge exchange model in the SPEX code v3.03, we re-analyze an archival Hubble STIS data of the central region of NGC 1275. The NGC 1275 spectrum shows hints for three possible weak lines at about 1223.6~{\AA}, 1242.4~{\AA}, and 1244.0~{\AA}, each with a significance of about $2-3\sigma$. The putative features are best explained by charge exchange between highly ionized hydrogen, neon, and sulfur with neutral matter. The wavelengths of the charge exchange lines are found robustly with uncertainties $\leq 0.3$~{\AA}. The possible charge exchange emission shows a line-of-sight velocity offset of about $-3400$ km s$^{-1}$ with respect to the NGC 1275 nucleus, which resembles one of the Ly$\alpha$ absorbers reported in Baum et al. (2005). This indicates that the charge exchange lines might be emitted as the same position of the absorber, which could be ascribed to outflowing gas from the nucleus.

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L. Gu, J. Mao, C. ODea, et. al.
Mon, 6 Mar 17
1/47

Comments: accepted for publication in A&A

Radiative association of C(${}^3P$) and H${}^+$: Triplet states [CL]

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http://arxiv.org/abs/1702.07777


The radiative association of C(${}^3P$) and H${}^+$ is investigated by calculating cross sections for photon emission into bound ro-vibrational states of CH${}^+$ from the vibrational continua of initial triplet d$\,{}^3\Pi$ or b$\,{}^3\Sigma^-$ states. Potential energy curves and transition dipole moments are calculated using multi-reference configuration interaction (MRCI) methods with AV6Z basis sets. The cross sections are evaluated using quantum-mechanical methods and rate coefficients are calculated. The rate coefficients are about 100 times larger than those for radiative association of C${}^+({}^2{P^o})$ and H from the A$\,{}^1\Pi$ state. We also confirm that the formation of CH${}^+$ by radiative association of C${}^+({}^2{P^o})$ and H via the triplet c$\,{}^3\Sigma^+$ state is a minor process.

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J. Babb and B. McLaughlin
Tue, 28 Feb 17
45/69

Comments: 7 pages

Experimental demonstration of a fifth force due to chameleon field via cold atoms [CEA]

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http://arxiv.org/abs/1702.03050


We tested a fifth force using cold atom experiments. The accelerated expansion of the universe implies the possibility of the presence of a scalar field throughout the universe driving the acceleration. This field would result in a detectable force between normal-matter objects. Theory of the chameleon field states that the force should be strong in a thin shell near the surface of a source object but greatly suppressed inside and outside of the source object. We used two atom clouds: one as the source and the other as the test mass; so the test mass can pass through the thin-shell region of the source mass. We detected the chameleon force and obtained the couple constant of about 4.5E11 between matter and the field. The chameleon force is considerably larger than Newtonian gravity at short distance; the interaction range is short enough to satisfy all experimental bounds on deviations from general relativity.

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H. Zhang
Mon, 13 Feb 17
12/57

Comments: 18 pages, 5 figures

Testing atomic collision theory with the two-photon continuum of astrophysical nebulae [CEA]

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http://arxiv.org/abs/1701.07913


Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abundances and recombination. There are now several competing theories for the treatment of this process, and it is not possible to test these experimentally. We show that the H I two-photon continuum produced by astrophysical nebulae is strongly affected by l-changing collisions. We perform an analysis of the different underlying atomic processes and simulate the recombination and two-photon spectrum of a nebula containing H and He. We provide an extended set of effective recombination coefficients and updated l-changing 2s-2p transition rates using several competing theories. In principle, accurate astronomical observations could determine which theory is correct.

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F. Guzman, N. Badnell, M. Chatzikos, et. al.
Mon, 30 Jan 17
24/41

Comments: 7 pages, 6 fig, 2 tables, accepted in MNRAS

PAMOP project: computations in support of experiments and astrophysical applications [CL]

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http://arxiv.org/abs/1701.03962


Our computation effort is primarily concentrated on support of current and future measurements being carried out at various synchrotron radiation facilities around the globe, and photodissociation computations for astrophysical applications. In our work we solve the Schr\”odinger or Dirac equation for the appropriate collision problem using the R-matrix or R-matrix with pseudo-states approach from first principles. The time dependent close-coupling (TDCC) method is also used in our work. A brief summary of the methodology and ongoing developments implemented in the R-matrix suite of Breit-Pauli and Dirac-Atomic R-matrix codes (DARC) is presented.

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B. McLaughlin, C. Ballance, M. Pindzola, et. al.
Tue, 17 Jan 17
13/81

Comments: 17 pages, 10 figures: chapter in the book, High Performance Computing in Science and Engineering’16, edited by W. E. Nagel, D. B. Kr\”oner, and M. Reich (Springer, New York and Berlin, 2017)

Radiative data for highly excited 3d8 4d levels in Ni II from laboratory measurements and atomic calculations [SSA]

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http://arxiv.org/abs/1701.02480


This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions from 3d8 4d levels of astrophysical interest in singly ionized nickel. Radiative lifetimes of seven high-lying levels of even parity in Ni II (98400 -100600 cm-1) have been measured using the time-resolved laser-induced fluorescence method. Two-step photon excitation of ions produced by laser ablation has been utilized to populate the levels. Theoretical calculations of the radiative lifetimes of the measured levels and transition probabilities from these levels are reported. The calculations have been performed using a pseudo-relativistic Hartree-Fock method, taking into account core polarization effects. A new set of transition probabilities and oscillator strengths has been deduced for 477 Ni II transitions of astrophysical interest in the spectral range 194 – 520 nm depopulating even parity 3d8 4d levels. The new calculated gf-values are, on the average, about 20 % higher than a previous calculation by Kurucz (this http URL) and yield lifetimes within 5 % of the experimental values.

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H. Hartman, L. Engstrom, H. Lundberg, et. al.
Wed, 11 Jan 17
17/64

Comments: 17 pages

Testing sub-gravitational forces on atoms from a miniature, in-vacuum source mass [CL]

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http://arxiv.org/abs/1612.05171


Gravity is the weakest fundamental interaction and the only one that has not been measured at the particle level. Traditional experimental methods, from astronomical observations to torsion balances, use macroscopic masses to both source and probe gravitational fields. Matter wave interferometers have used neutrons, atoms and molecular clusters as microscopic test particles, but initially probed the field sourced by the entire earth. Later, the gravitational field arising from hundreds of kilograms of artificial source masses was measured with atom interferometry. Miniaturizing the source mass and moving it into the vacuum chamber could improve positioning accuracy, allow the use of monocrystalline source masses for improved gravitational measurements, and test new physics, such as beyond-standard-model (“fifth”) forces of nature and non-classical effects of gravity. In this work, we detect the gravitational force between freely falling cesium atoms and an in-vacuum, centimeter-sized source mass using atom interferometry with state-of-the-art sensitivity. The ability to sense gravitational-strength coupling is conjectured to access a natural lower bound for fundamental forces, thereby representing an important milestone in searches for physics beyond the standard model. A local, in-vacuum source mass is particularly sensitive to a wide class of interactions whose effects would otherwise be suppressed beyond detectability in regions of high matter density. For example, our measurement strengthens limits on a number of cosmologically-motivated scalar field models, such as chameleon and symmetron fields, by over two orders of magnitude and paves the way toward novel measurements of Newton’s gravitational constant G and the gravitational Aharonov-Bohm effect

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M. Jaffe, P. Haslinger, V. Xu, et. al.
Fri, 16 Dec 16
46/60

Comments: N/A

Stellar laboratories. VIII. New Zr IV – VII, Xe IV – V, and Xe VII oscillator strengths and the Al, Zr, and Xe abundances in the hot white dwarfs G191-B2B and RE0503-289 [CL]

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http://arxiv.org/abs/1611.07364


For the spectral analysis of high-resolution and high-signal-to-noise spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation.
To search for Zr and Xe lines in the ultraviolet (UV) spectra of G191-B2B and RE0503-289, new Zr IV-VII, Xe IV-V, and Xe VIII oscillator strengths were calculated. This allows for the first time, determination of the Zr abundance in white dwarf (WD) stars and improvement of the Xe abundance determinations.
We calculated Zr IV-VII, Xe IV-V, and Xe VIII oscillator strengths to consider radiative and collisional bound-bound transitions of Zr and Xe in our NLTE stellar-atmosphere models for the analysis of their lines exhibited in UV observations of the hot WDs G191-B2B and RE0503-289.
We identified one new Zr IV, 14 new Zr V, and ten new Zr VI lines in the spectrum of RE0503-289. Zr was detected for the first time in a WD. We measured a Zr abundance of -3.5 +/- 0.2 (logarithmic mass fraction, approx. 11 500 times solar). We dentified five new Xe VI lines and determined a Xe abundance of -3.9 +/- 0.2 (approx. 7500 times solar). We determined a preliminary photospheric Al abundance of -4.3 +/- 0.2 (solar) in RE0503-289. In the spectra of G191-B2B, no Zr line was identified. The strongest Zr IV line (1598.948 A) in our model gave an upper limit of -5.6 +/- 0.3 which is about 100 times solar. No Xe line was identified in the UV spectrum of G191-B2B and we confirmed the previously determined upper limit of -6.8 +/- 0.3 (ten times solar).
Precise measurements and calculations of atomic data are a prerequisite for advanced NLTE stellar-atmosphere modeling. Observed Zr IV – VI and Xe VI – VII line profiles in the UV spectrum of RE0503-289 were simultaneously well reproduced.

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T. Rauch, S. Gamrath, P. Quinet, et. al.
Wed, 23 Nov 16
5/68

Comments: 137 pages, 11 figures

Non-Elastic Processes in Atom Rydberg-Atom Collisions: Review of State of Art and Problems [CL]

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http://arxiv.org/abs/1611.06333


In our previous research, it has been demonstrated that such inelastic processes in atom Rydberg-atom collisions, as chemi-ionization and (n-n’) mixing, should be considered together. Here we will review the present state of the art and the actual problems will be discussed. In this context, we will consider the influence of the (n-n’)-mixing during a symmetric atom Rydberg-atom collision processes on the intensity of chemi-ionization process. It will be taken into account H(1s) + H*(n) collisional systems, where the principal quantum number n $>>$ 1. It will be demonstrated that the inclusion of (n-n’) mixing in the calculation, influences significantly on the values of chemi-ionization rate coefficients, particularly in the lower part of the block of the Rydberg states. Different possible channels of the (n-n’)-mixing influence on chemi-ionization rate coefficients will be demonstrated. The possibility of interpretation of the (n-n’)-mixing influence will be considered on the basis of two existing methods for describing of the inelastic processes in symmetrical atom Rydberg-atom collisions.

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A. Mihajlov, V. Sreckovic, L. Ignjatovic, et. al.
Tue, 22 Nov 16
77/79

Comments: 7 pages, 2 figures

Energy levels, radiative rates and electron impact excitation rates for transitions in Si III [CL]

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http://arxiv.org/abs/1611.04585


Energy levels and radiative rates (A-values) for four types of transitions (E1, E2, M1, and M2) are reported for an astrophysically important Mg-like ion Si~III, whose emission lines have been observed in a variety of plasmas. For the calculations, well-known and widely-used GRASP code has been adopted, and results are listed for transitions among the 141 levels of the 3$\ell3\ell’$ and 3$\ell$4$\ell$ configurations. Experimental energies are available for only the lowest 58 levels but there is no major discrepancy with theoretical results. Similarly, the A-values and lifetimes show a satisfactory agreement with other available results, particularly for strong E1 transitions. Collision strengths are also calculated, with the DARC code, and listed for resonance transitions over a wide energy range, up to 30~Ryd. No similar results are available in the literature for comparisons. However, comparisons are made with the more important parameter, effective collision strength ($\Upsilon$), for which recent $R$-matrix results are available for a wide range of transitions, and over a large range of temperatures. To determine $\Upsilon$, resonances have been resolved in a narrow energy mesh, although these are not observed to be as important as for other ions. Unfortunately, large discrepancies in $\Upsilon$ values are noted for about half the transitions. The differences increase with increasing temperature and worsen as the upper level J increases. In most cases the earlier results are overestimated, by up to (almost) two orders of magnitude, and this conclusion is consistent with the one observed earlier for Be-like ions.

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K. Aggarwal
Wed, 16 Nov 16
63/64

Comments: 17 pages of text including 6 figures and 4 Tables will be published in ADNDT (2017)

Hot DA white dwarf model atmosphere calculations: Including improved Ni PI cross sections [SSA]

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http://arxiv.org/abs/1610.09662


To calculate realistic models of objects with Ni in their atmospheres, accurate atomic data for the relevant ionization stages needs to be included in model atmosphere calculations. In the context of white dwarf stars, we investigate the effect of changing the Ni {\sc iv}-{\sc vi} bound-bound and bound-free atomic data has on model atmosphere calculations. Models including PICS calculated with {\sc autostructure} show significant flux attenuation of up to $\sim 80$\% shortward of 180\AA\, in the EUV region compared to a model using hydrogenic PICS. Comparatively, models including a larger set of Ni transitions left the EUV, UV, and optical continua unaffected. We use models calculated with permutations of this atomic data to test for potential changes to measured metal abundances of the hot DA white dwarf G191-B2B. Models including {\sc autostructure} PICS were found to change the abundances of N and O by as much as $\sim 22$\% compared to models using hydrogenic PICS, but heavier species were relatively unaffected. Models including {\sc autostructure} PICS caused the abundances of N/O {\sc iv} and {\sc v} to diverge. This is because the increased opacity in the {\sc autostructure} PICS model causes these charge states to form higher in the atmosphere, moreso for N/O {\sc v}. Models using an extended line list caused significant changes to the Ni {\sc iv}-{\sc v} abundances. While both PICS and an extended line list cause changes in both synthetic spectra and measured abundances, the biggest changes are caused by using {\sc autostructure} PICS for Ni.

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S. Preval, M. Barstow, N. Badnell, et. al.
Tue, 1 Nov 16
1/75

Comments: 14 pages, 9 figures, 7 tables. Accepted for publication in MNRAS

Infrared Opacities in Dense Atmospheres of Cool White Dwarf Stars [SSA]

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http://arxiv.org/abs/1610.07357


Dense, He-rich atmospheres of cool white dwarfs represent a challenge to the modeling. This is because these atmospheres are constituted of a dense fluid in which strong multi-atomic interactions determine their physics and chemistry. Therefore, the ideal-gas-based description of absorption is no longer adequate, which makes the opacities of these atmospheres difficult to model. This is illustrated with severe problems in fitting the spectra of cool, He-rich stars. Good description of the infrared (IR) opacity is essential for proper assignment of the atmospheric parameters of these stars. Using methods of computational quantum chemistry we simulate the IR absorption of dense He/H media. We found a significant IR absorption from He atoms (He-He-He CIA opacity) and a strong pressure distortion of the H$_2$-He collision-induced absorption (CIA). We discuss the implication of these results for interpretation of the spectra of cool stars.

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P. Kowalski, S. Blouin and P. Dufour
Tue, 25 Oct 16
54/69

Comments: 6 pages, 5 figures, Proceedings of the EUROWD2016 workshop. To be published in ASPCS

Laser remote magnetometry using mesospheric sodium [IMA]

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http://arxiv.org/abs/1610.05385


We have demonstrated a remote magnetometer based on sodium atoms in the Earth’s mesosphere, at a 106-kilometer distance from our instrument. A 1.33-watt laser illuminated the atoms, and the magnetic field was inferred from back-scattered light collected by a telescope with a 1.55-meter-diameter aperture. The measurement sensitivity was 162 nT/$\sqrt{Hz}$. The value of magnetic field inferred from our measurement is consistent with an estimate based on the Earth’s known field shape to within a fraction of a percent. Projected improvements in optics could lead to sensitivity of 20 nT/$\sqrt{Hz}$, and the use of advanced lasers or a large telescope could approach 1-nT/$\sqrt{Hz}$ sensitivity. All experimental and theoretical sensitivity values are based on a 60{\deg} angle between the laser beam axis and the magnetic field vector; at the optimal 90{\deg} angle sensitivity would be improved by about a factor of two.

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T. Kane, P. Hillman, C. Denman, et. al.
Wed, 19 Oct 16
31/87

Comments: 15 pages, 15 figures, 4 tables

Modeling the Spectra of Dense Hydrogen Plasmas: Beyond Occupation Probability [SSA]

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http://arxiv.org/abs/1610.02342


Accurately measuring the masses of white dwarf stars is crucial in many astrophysical contexts (e.g., asteroseismology and cosmochronology). These masses are most commonly determined by fitting a model atmosphere to an observed spectrum; this is known as the spectroscopic method. However, for cases in which more than one method may be employed, there are well known discrepancies between masses determined by the spectroscopic method and those determined by astrometric, dynamical, and/or gravitational-redshift methods. In an effort to resolve these discrepancies, we are developing a new model of hydrogen in a dense plasma that is a significant departure from previous models. Experiments at Sandia National Laboratories are currently underway to validate these new models, and we have begun modifications to incorporate these models into stellar-atmosphere codes.

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T. Gomez, M. Montgomery, T. Nagayama, et. al.
Mon, 10 Oct 16
44/51

Comments: 6 pages, 4 figures, to appear in the Proceedings of The 20th European Workshop on White Dwarfs

Photoionisation of Cl$^+$ from the $3s^23p^4\;^3P_{2,1,0}$ and the$3s^23p^4\;^1D_2, ^1S_0$ states in the energy range 19 – 28 eV [CL]

Posted on by

http://arxiv.org/abs/1609.09722


Absolute photoionisation cross sections for the Cl$^+$ ion in its ground and the metastable states; $3s^2 3p^4\; ^3P_{2,1,0}$, and $3s^2 3p^4\; ^1D_2,\; ^1S_0$, were measured recently at the Advanced Light Source ALS) at Lawrence Berkeley National Laboratory using the merged beams photon-ion technique at an photon energy resolution of 15 meV in the energy range 19 — 28 eV. These measurements are compared with large-scale Dirac Coulomb {\it R}-matrix calculations in the same energy range. Photoionisation of this sulphur-like chlorine ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionisation continuum. A wealth of resonance features observed in the experimental spectra are spectroscopically assigned and their resonance parameters tabulated and compared with the recent measurements. Metastable fractions in the parent ion beam are determined from the present study. Theoretical resonance energies and quantum defects of the prominent Rydberg series $3s^2 3p^3 nd$, identified in the spectra as $3p\rightarrow nd$ transitions are compared with the available measurements made on this element. Weaker Rydberg series $3s^2 3p^3 ns$, identified as $3p \rightarrow ns$ transitions and window resonances $3s3p^4 (^4P)np$ features, due to $3s \rightarrow np$ transitions are also found in the spectra.

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B. McLaughlin
Mon, 3 Oct 16
46/47

Comments: 12 pages, 5 figures, 3 tables., accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:1412.8715

Electron impact excitation rates for transitions in Mg V [CL]

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http://arxiv.org/abs/1609.08351


Energy levels, radiative rates (A-values) and lifetimes, calculated with the GRASP code, are reported for an astrophysically important O-like ion Mg~V. Results are presented for transitions among the lowest 86 levels belonging to the 2s$^2$2p$^4$, 2s2p$^5$, 2p$^6$, and 2s$^2$2p$^3$3$\ell$ configurations. There is satisfactory agreement with earlier data for most levels/transitions, but scope remains for improvement. Collision strengths are also calculated, with the DARC code, and the results obtained are comparable for most transitions (at energies above thresholds) with earlier work using the DW code. In thresholds region, resonances have been resolved in a fine energy mesh to determine values of effective collision strengths ($\Upsilon$) as accurately as possible. Results are reported for all transitions at temperatures up to 10$^6$~K, which should be sufficient for most astrophysical applications. However, a comparison with earlier data reveals discrepancies of up to two orders of magnitude for over 60\% of transitions, at all temperatures. The reasons for these discrepancies are discussed in detail.

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K. Aggarwal and F. Keenan
Wed, 28 Sep 16
39/60

Comments: 11p of Text, 6 Tables and 6 Figures will appear in Canadian J. Physics (2017)

Lifetimes and Oscillator Strengths for Ultraviolet Transitions in Singly-Ionized Tin [CL]

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http://arxiv.org/abs/1609.07047


Lifetime measurements using beam foil techniques for the $5s5p^{2}$ $^{2}D_{3/2,5/2}$ levels in Sn II are presented. The resulting oscillator strengths for transitions at 1699.4, 1831.8 and 1811.2 \AA{} are reported. We also studied these levels with multi-configuration Dirac Hartree-Fock (MCDHF) calculations using a development version of the GRASP2K package. Our experimental and theoretical results are compared with other available studies.

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N. Heidarian, R. Irving, S. Federman, et. al.
Fri, 23 Sep 16
26/50

Comments: N/A

Experimental radiative lifetimes for highly excited states and calculated oscillator strengths for lines of astrophysical interest in singly ionized cobalt (Co II) [SSA]

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http://arxiv.org/abs/1609.02183


This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions of astrophysical interest in singly ionized cobalt. More pre- cisely, nineteen radiative lifetimes in Co+ have been measured with the time-resolved laser-induced fluorescence technique using one- and two-step excitations. Out of these, seven belonging to the high lying 3d$^7$($^4$F)4d configuration in the energy range 90697 – 93738 cm$^{-1}$ are new, and the other twelve from th3d$^7$($^4$F)F)4p configuration with energies between 45972 and 49328 cm$^{-1}$1 are compared with previous measurements. In addition, a relativistic Hartree-Fock model including core-polarization e?ects has been employed to compute transition rates. Supported by the good agreement between theory and experiment for the lifetimes, new reliable transition probabilities and os- cillator strengths have been deduced for 5080 Co II transitions in the spectral range 114 – 8744 nm.

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P. Quinet, V. Fivet, P. Palmeri, et. al.
Fri, 9 Sep 16
3/70

Comments: N/A

Laboratory Measurements of the K-shell transition energies in L-shell ions of Si and S [CL]

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http://arxiv.org/abs/1609.00403


We have measured the energies of the strongest 1s-2ell (ell=s,p) transitions in He- through Ne-like silicon and sulfur ions to an accuracy of better than 1eV using Lawrence Livermore National Laboratory’s electron beam ion traps, EBIT-I and SuperEBIT, and the NASA/GSFC EBIT Calorimeter Spectrometer (ECS). We identify and measure the energies of 18 and 21 X-ray features from silicon and sulfur, respectively. The results are compared to new Flexible Atomic Code calculations and to semi-relativistic Hartree Fock calculations by Palmeri et al. (2008). These results will be especially useful for wind diagnostics in high mass X-ray binaries, such as Vela X-1 and Cygnus X-1, where high-resolution spectral measurements using Chandra’s high energy transmission grating has made it possible to measure Doppler shifts of 100km/s. The accuracy of our measurements is consistent with that needed to analyze Chandra observations, exceeding Chandra’s 100km/s limit. Hence, the results presented here not only provide benchmarks for theory, but also accurate rest energies that can be used to determine the bulk motion of material in astrophysical sources. We show the usefulness of our results by applying them to redetermine Doppler shifts from Chandra observations of Vela X-1.

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N. Hell, G. Brown, J. Wilms, et. al.
Mon, 5 Sep 16
14/57

Comments: ApJ, in press

H, He-like recombination spectra II: $l$-changing collisions for He Rydberg states [CEA]

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http://arxiv.org/abs/1608.08947


Cosmological models can be constrained by determining primordial abundances. Accurate predictions of the He I spectrum are needed to determine the primordial helium abundance to a precision of $< 1$% in order to constrain Big Bang Nucleosynthesis models. Theoretical line emissivities at least this accurate are needed if this precision is to be achieved. In the first paper of this series, which focused on H I, we showed that differences in $l$-changing collisional rate coefficients predicted by three different theories can translate into 10% changes in predictions for H I spectra. Here we consider the more complicated case of He atoms, where low-$l$ subshells are not energy degenerate. A criterion for deciding when the energy separation between $l$ subshells is small enough to apply energy-degenerate collisional theories is given. Moreover, for certain conditions, the Bethe approximation originally proposed by Pengelly & Seaton (1964) is not sufficiently accurate. We introduce a simple modification of this theory which leads to rate coefficients which agree well with those obtained from pure quantal calculations using the approach of Vrinceanu et al. (2012). We show that the $l$-changing rate coefficients from the different theoretical approaches lead to differences of $\sim 10$% in He I emissivities in simulations of H II regions using spectral code Cloudy.

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F. Guzman, N. Badnell, R. Williams, et. al.
Thu, 1 Sep 16
34/74

Comments: 9 pages, $ figures, 2 tables, accepted for publication in MNRAS

Plasma-screening effects in the atrophysically relevant He-like and Li-like Mg and Fe ions [CL]

Posted on by

http://arxiv.org/abs/1608.07919


The effect of plasma environment on the atomic energy levels of He-like and Li-like Mg and Fe ions have been studied using Debye model. The equation-of-motion coupled-cluster (EOMCC) and Fock-space coupled-cluster (FSCC) formalisms in the relativistic frame work have been adopted to describe the atomic states and the energy levels of the above plasma embedded ions. Salient features of these methods have been described to account the two electron screening effects through the Debye potentials. The two-body screening potential has been derived in the multipole expansion form to evaluate the reduced matrix elements in solving the equation of motion. Using this extended model, we have also predicted that quasi-degeneracy among the energy states having same principal quantum number ($n$) but different angular momentum ($l$) is slacken, whereas fine structure splitting is unaffected with increasing plasma strength. These knowledge are useful in estimatingradiative opacity, photoionization cross sections, line intensities, etc of the aforementioned astrophysical plasmas.

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B. Sahoo and M. Das
Tue, 30 Aug 16
30/78

Comments: 10 pages, 5 tables and 4 figures

Laboratory measurements compellingly support charge-exchange mechanism for the 'dark matter' $\sim$3.5 keV X-ray line [HEAP]

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http://arxiv.org/abs/1608.04751


The reported observations of an unidentified X-ray line feature at $\sim$3.5 keV have driven a lively discussion about its possible dark matter origin. Motivated by this, we have measured the \emph{K}-shell X-ray spectra of highly ionized bare sulfur ions following charge exchange with gaseous molecules in an electron beam ion trap, as a source of or a contributor to this X-ray line. We produce $\mathrm{S}^{16+}$ and $\mathrm{S}^{15+}$ ions and let them capture electrons in collision with those molecules with the electron beam turned off while recording X-ray spectra. We observed a charge-exchanged-induced X-ray feature at the Lyman series limit (3.47 $\pm$ 0.06 keV). The inferred X-ray energy is in full agreement with the reported astrophysical observations and supports the novel scenario proposed by Gu and Kaastra (A \& A \textbf{584}, {L11} (2015)).

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C. Shah, S. Dobrodey, S. Bernitt, et. al.
Thu, 18 Aug 16
9/51

Comments: 7 pages, 6 figures, accepted for publication in ApJ

Electron impact excitation of N IV: calculations with the DARC code and a comparison with ICFT results [CL]

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http://arxiv.org/abs/1608.04406


There have been discussions in the recent literature regarding the accuracy of the available electron impact excitation rates (equivalently effective collision strengths $\Upsilon$) for transitions in Be-like ions. In the present paper we demonstrate, once again, that earlier results for $\Upsilon$ are indeed overestimated (by up to four orders of magnitude), for over 40\% of transitions and over a wide range of temperatures. To do this we have performed two sets of calculations for N~IV, with two different model sizes consisting of 166 and 238 fine-structure energy levels. As in our previous work, for the determination of atomic structure the GRASP (General-purpose Relativistic Atomic Structure Package) is adopted and for the scattering calculations (the standard and parallelised versions of) the Dirac Atomic R-matrix Code ({\sc darc}) are employed. Calculations for collision strengths and effective collision strengths have been performed over a wide range of energy (up to 45~Ryd) and temperature (up to 2.0$\times$10$^6$~K), useful for applications in a variety of plasmas. Corresponding results for energy levels, lifetimes and A-values for all E1, E2, M1 and M2 transitions among 238 levels of N~IV are also reported.

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K. Aggarwal, F. Keenan and K. Lawson
Wed, 17 Aug 16
29/48

Comments: This paper with 5 Figs. and 8 Tables will appear in MNRAS (2016)

Comment on "Large enhancement in high-energy photoionization of Fe XVII and missing continuum plasma opacity" [CL]

Posted on by

http://arxiv.org/abs/1608.03512


Recent R-matrix calculations claim to produce a significant enhancement in the opacity of Fe XVII due to atomic core excitations [S. N. Nahar & A.K. Pradhan, Phys. Rev. Letters 116, 235003 (2016), arXiv:1606.02731] and assert that this enhancement is consistent with recent measurements of higher-than-predicted iron opacities [J. E. Bailey et al., Nature 517, 56 (2015)]. This comment shows that the standard opacity models which have already been directly compared with experimental data produce photon absorption cross-sections for Fe XVII that are effectively equivalent to (and in fact larger than) the new R-matrix opacities. Thus, the new R-matrix results cannot be expected to significantly impact the existing discrepancies between theory and experiment because they produce neither a “large enhancement” nor account for “missing continuum plasma opacity” relative to standard models.

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C. Blancard, J. Colgan, P. Cosse, et. al.
Fri, 12 Aug 16
24/38

Comments: three pages, one table, one figure

Suzaku and XMM-Newton Observations of the North Polar Spur: Charge Exchange or ISM Absorption? [HEAP]

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http://arxiv.org/abs/1607.08334


By revisiting the Suzaku and XMM-Newton data of the North Polar Spur, we discovered that the spectra are inconsistent with the traditional model consisting of pure thermal emission and neutral absorption. The most prominent discrepancies are the enhanced O VII and Ne IX forbidden-to-resonance ratios, and a high O VIII Ly$\beta$ line relative to other Lyman series. A collisionally ionized absorption model can naturally explain both features, while a charge exchange component can only account for the former. By including the additional ionized absorption, the plasma in the North Polar Spur can be described by a single-phase CIE component with temperature of 0.25 keV, and nitrogen, oxygen, neon, magnesium, and iron abundances of $0.4-0.8$ solar. The abundance pattern of the North Polar Spur is well in line with those of the Galactic halo stars. The high nitrogen-to-oxygen ratio reported in previous studies can be migrated to the large transmission of the O VIII Ly$\alpha$ line. The ionized absorber is characterized by a balance temperature of $0.17-0.20$ keV and a column density of $3-5 \times 10^{19}$ cm$^{-2}$. Based on the derived abundances and absorption, we speculate that the North Polar Spur is a structure in the Galactic halo, so that the emission is mostly absorbed by Galactic ISM in the line of sight.

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L. Gu, J. Mao, E. Costantini, et. al.
Fri, 29 Jul 16
7/44

Comments: Accepted for publication in Astronomy and Astrophysics

Density diagnostics derived from the OIV and SIV intercombination lines observed by IRIS [SSA]

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http://arxiv.org/abs/1607.05072


The intensity of the \oiv~2s$^{2}$ 2p $^{2}$P-2s2p$^{2}$ $^{4}$P and \siv~3 s$^{2}$ 3p $^{2}$P- 3s 3p$^{2}$ $^{4}$ P intercombination lines around 1400~\AA~observed with the \textit{Interface Region Imaging Spectrograph} (IRIS) provide a useful tool to diagnose the electron number density ($N_\textrm{e}$) in the solar transition region plasma. We measure the electron number density in a variety of solar features observed by IRIS, including an active region (AR) loop, plage and brightening, and the ribbon of the 22-June-2015 M 6.5 class flare. By using the emissivity ratios of \oiv\ and \siv\ lines, we find that our observations are consistent with the emitting plasma being near isothermal (log$T$[K] $\approx$ 5) and iso-density ($N_\textrm{e}$ $\approx$~10$^{10.6}$ cm$^{-3}$) in the AR loop. Moreover, high electron number densities ($N_\textrm{e}$ $\approx$~10$^{13}$ cm$^{-3}$) are obtained during the impulsive phase of the flare by using the \siv\ line ratio. We note that the \siv\ lines provide a higher range of density sensitivity than the \oiv\ lines. Finally, we investigate the effects of high densities ($N_\textrm{e}$ $\gtrsim$ 10$^{11}$ cm$^{-3}$) on the ionization balance. In particular, the fractional ion abundances are found to be shifted towards lower temperatures for high densities compared to the low density case. We also explored the effects of a non-Maxwellian electron distribution on our diagnostic method.

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V. Polito, G. Zanna, J. Dudik, et. al.
Tue, 19 Jul 16
37/68

Comments: N/A

Scaling of collision strengths for highly-excited states of ions of the H- and He-like sequences [IMA]

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http://arxiv.org/abs/1607.02487


Emission lines from highly-excited states (n >= 5) of H- and He-like ions have been detected in astrophysical sources and fusion plasmas. For such excited states, R-matrix or distorted wave calculations for electron-impact excitation are very limited, due to the large size of the atomic basis set needed to describe them. Calculations for n >= 6 are also not generally available. We study the behaviour of the electron-impact excitation collision strengths and effective collision strengths for the most important transitions used to model electron collision dominated astrophysical plasmas, solar, for example. We investigate the dependence on the relevant parameters: the principal quantum number n or the nuclear charge Z. We also estimate the importance of coupling to highly-excited states and the continuum by comparing the results of different sized calculations. We provide analytic formulae to calculate the electron-impact excitation collision strengths and effective collision strengths to highly-excited states (n >= 8) of H- and He-like ions. These extrapolated effective collision strengths can be used to interpret astrophysical and fusion plasma via collisional-radiative modelling.

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L. Fernandez-Menchero, G. Zanna and N. Badnell
Mon, 11 Jul 16
4/62

Comments: 9 pages, 11 figures, 5 tables, online material

Strong higher-order resonant contributions to x-ray line polarization in hot plasmas [CL]

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http://arxiv.org/abs/1606.06776


We studied angular distributions of x rays emitted in resonant recombination of highly charged iron and krypton ions, resolving dielectronic, trielectronic, and quadruelectronic channels. A tunable electron beam drove these processes, inducing x rays registered by two detectors mounted along and perpendicular to the beam axis. The measured emission asymmetries comprehensively benchmarked full-order atomic calculations. We conclude that accurate polarization diagnostics of hot plasmas can only be obtained under the premise of inclusion of higher-order processes that were neglected in earlier work.

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C. Shah, P. Amaro, R. Steinbrugge, et. al.
Thu, 23 Jun 16
49/49

Comments: 8 pages, 3 figures

Precise limits on cosmological variability of the fine-structure constant with zinc and chromium quasar absorption lines [CEA]

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http://arxiv.org/abs/1606.06293


The strongest transitions of Zn and CrII are the most sensitive to relative variations in the fine-structure constant ($\Delta\alpha/\alpha$) among the transitions commonly observed in quasar absorption spectra. They also lie within just 40 \AA\ of each other (rest frame), so they are resistant to the main systematic error affecting most previous measurements of $\Delta\alpha/\alpha$: long-range distortions of the wavelength calibration. While Zn and CrII absorption is normally very weak in quasar spectra, we obtained high signal-to-noise, high-resolution echelle spectra from the Keck and Very Large Telescopes of 9 rare systems where it is strong enough to constrain $\Delta\alpha/\alpha$ from these species alone. These provide 12 independent measurements (3 quasars were observed with both telescopes) at redshifts 1.0–2.4, 11 of which pass stringent reliability criteria. These 11 are all consistent with $\Delta\alpha/\alpha=0$ within their individual uncertainties of 3.5–13 parts per million (ppm), with a weighted mean $\Delta\alpha/\alpha = 0.4\pm1.4_{\rm stat}\pm0.9_{\rm sys}$ ppm (1$\sigma$ statistical and systematic uncertainties), indicating no significant cosmological variations in $\alpha$. This is the first statistical sample of absorbers that is resistant to long-range calibration distortions (at the $<$1 ppm level), with a precision comparable to previous large samples of $\sim$150 (distortion-affected) absorbers. Our systematic error budget is instead dominated by much shorter-range distortions repeated across echelle orders of individual spectra.

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M. Murphy, A. Malec and J. Prochaska
Wed, 22 Jun 16
28/50

Comments: 20 pages, 15 figures. Accepted by MNRAS. Quasar spectra and Zn/CrII absorption profile fits are available at this http URL

Polarization measurement of dielectronic recombination transitions in highly charged krypton ions [CL]

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http://arxiv.org/abs/1606.06334


We report linear polarization measurements of x rays emitted due to dielectronic recombination into highly charged krypton ions. The ions in the He-like through O-like charge states were populated in an electron beam ion trap with the electron beam energy adjusted to recombination resonances in order to produce $K\alpha$ x rays. The x rays were detected with a newly developed Compton polarimeter using a beryllium scattering target and 12 silicon x-ray detector diodes sampling the azimuthal distribution of the scattered x rays. The extracted degrees of linear polarization of several dielectronic recombination transitions agree with results of relativistic distorted–wave calculations. We also demonstrate a high sensitivity of the polarization to the Breit interaction, which is remarkable for a medium-$Z$ element like krypton. The experimental results can be used for polarization diagnostics of hot astrophysical and laboratory fusion plasmas.

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C. Shah, H. Jorg, S. Bernitt, et. al.
Wed, 22 Jun 16
43/50

Comments: 11 pages, 4 figures

A Resonant Mode for Gravitational Wave Detectors based on Atom Interferometry [CL]

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http://arxiv.org/abs/1606.01860


We describe a new atom interferometric gravitational wave detector design that can operate in a resonant mode for increased sensitivity. By oscillating the positions of the atomic wavepackets, this resonant detection mode allows for coherently enhanced, narrow-band sensitivity at target frequencies. The proposed detector is flexible and can be rapidly switched between broadband and narrow-band detection modes without changing hardware. For instance, a new binary discovered in broadband mode can subsequently be studied further as the inspiral evolves by using a tailored narrow-band detector response. In addition to functioning like a lock-in amplifier for astrophysical events, the enhanced sensitivity of the resonant approach also opens up the possibility of searching for important cosmological signals, including the stochastic gravitational wave background produced by inflation. We give an example of detector parameters which would allow detection of inflationary gravitational waves down to $\Omega_\text{GW} \sim 10^{-14}$ for a two satellite space-based detector.

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P. Graham, J. Hogan, M. Kasevich, et. al.
Tue, 7 Jun 16
6/80

Comments: 7 pages, 4 figures

Gravitational wave detection with optical lattice atomic clocks [CL]

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http://arxiv.org/abs/1606.01859


We propose a space-based gravitational wave detector consisting of two spatially separated, drag-free satellites sharing ultra-stable optical laser light over a single baseline. Each satellite contains an optical lattice atomic clock, which serves as a sensitive, narrowband detector of the local frequency of the shared laser light. A synchronized two-clock comparison between the satellites will be sensitive to the effective Doppler shifts induced by incident gravitational waves (GWs) at a level competitive with other proposed space-based GW detectors, while providing complementary features. The detected signal is a differential frequency shift of the shared laser light due to the relative velocity of the satellites, rather than a phase shift arising from the relative satellite positions, and the detection window can be tuned through the control sequence applied to the atoms’ internal states. This scheme enables the detection of GWs from continuous, spectrally narrow sources, such as compact binary inspirals, with frequencies ranging from ~3 mHz – 10 Hz without loss of sensitivity, thereby bridging the detection gap between space-based and terrestrial GW detectors. Our proposed GW detector employs just two satellites, is compatible with integration with an optical interferometric detector, and requires only realistic improvements to existing ground-based clock and laser technologies.

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S. Kolkowitz, I. Pikovski, N. Langellier, et. al.
Tue, 7 Jun 16
52/80

Comments: 8 pages, 2 figures, and supplemental material

Detecting dark matter waves with precision measurement tools [CL]

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http://arxiv.org/abs/1605.09717


Virialized Ultra-Light Fields (VULFs) while being viable cold dark matter candidates can also solve the standard model hierarchy problem. Direct searches for VULFs due to their non-particle nature require low-energy precision measurement tools. Here we consider scalar VULF candidates. While the previous proposals have focused on detecting coherent oscillations of the measured signals at the VULF Compton frequencies at the device location, here we point out that VULFs also have a distinct spatial signature, forming dark matter waves. Thereby the discovery reach can be improved by using distributed networks of precision measurement tools. We find the expected dark-matter wave signal by deriving spatio-temporal two-point VULF correlation function. Based on the developed formalism for coherence properties of dark-matter fields, we propose several experiments for dark matter wave detection. In the most basic version, the modifications to already running experiments are minor and only require GPS-assisted time-stamping of data. We also derive the expected dark matter line profile for individual detectors.

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A. Derevianko
Wed, 1 Jun 16
29/59

Comments: 5 pages, 2 figs

Energy levels and radiative rates for transitions in Fe V, Co VI and Ni VII [CL]

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http://arxiv.org/abs/1605.08212


Energy levels, Land\'{e} $g$-factors and radiative lifetimes are reported for the lowest 182 levels of the 3d$^4$, 3d$^3$4s and 3d$^3$4p configurations of Fe~V, Co~VI and Ni~VII. Additionally, radiative rates ($A$-values) have been calculated for the E1, E2 and M1 transitions among these levels. The calculations have been performed in a quasi-relativistic approach (QR) with a very large {\em configuration interaction} (CI) wavefunction expansion, which has been found to be necessary for these ions. Our calculated energies for all ions are in excellent agreement with the available measurements, for most levels. Discrepancies among various calculations for the radiative rates of E1 transitions in Fe~V are up to a factor of two for stronger transitions ($f \geq 0.1$), and larger (over an order of magnitude) for weaker ones. The reasons for these discrepancies have been discussed and mainly are due to the differing amount of CI and methodologies adopted. However, there are no appreciable discrepancies in similar data for M1 and E2 transitions, or the $g$-factors for the levels of Fe~V, the only ion for which comparisons are feasible.

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K. Aggarwal, P. Bogdanovich, F. Keenan, et. al.
Fri, 27 May 16
8/56

Comments: This paper of 78 pages including 9 Tables will appear in ADNDT (2016)

Sensitivity of atom interferometry to ultralight scalar field dark matter [CL]

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http://arxiv.org/abs/1605.04048


We discuss the use of atom interferometry as a tool to search for Dark Matter (DM) composed of ultra-light scalar fields. Previous work on ultra-light DM detection using accelerometers has considered the possibility of equivalence principle violating effects whereby gradients in the dark matter field can directly produce relative accelerations between media of differing composition. In atom interferometers, we find that time-varying phase signals from oscillatory, or dilaton-like, DM can also arise due to changes in the atom rest mass that can occur between light-pulses throughout the interferometer sequence as well as changes in the earth’s gravitational field. We estimate that several orders of magnitude of unexplored phase space for light DM fields can be probed with our proposed method.

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A. Geraci and A. Derevianko
Mon, 16 May 16
8/48

Comments: 5 pages, 2 figures

Improved limits on interactions of low-mass spin-0 dark matter from atomic clock spectroscopy [CL]

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http://arxiv.org/abs/1605.04028


Low-mass (sub-eV) spin-0 dark matter particles, which form a coherently oscillating classical field $\phi = \phi_0 \cos(m_\phi t)$, can induce oscillating variations in the fundamental constants through their interactions with the Standard Model sector. We calculate the effects of such possible interactions, which may include the linear interaction of $\phi$ with the Higgs boson, on atomic and molecular transitions. Using recent atomic clock spectroscopy measurements, we derive new limits on the linear interaction of $\phi$ with the Higgs boson, as well as its quadratic interactions with the photon and light quarks. For the linear interaction of $\phi$ with the Higgs boson, our derived limits improve on existing constraints by up to $2-3$ orders of magnitude.

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Y. Stadnik and V. Flambaum
Mon, 16 May 16
25/48

Comments: 6 pages, 5 figures

Photon Bubble Turbulence in Cold Atomic Gases [CL]

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http://arxiv.org/abs/1604.08114


Turbulent radiation flow is ubiquitous in many physical systems where light-matter interaction becomes relevant. Photon bubbling, in particular, has been identified as the main source of turbulent radiation transport in many astrophysical objects, such as stars and accretion disks. This mechanism takes place when radiation trapping in optically dense media becomes unstable, leading to the energy dissipation from the larger to the smaller bubbles. Here, we report on the observation of photon bubble turbulence in cold atomic gases in the presence of multiple scattering of light. The instability is theoretically explained by a fluid description for the atom density coupled to a diffusive transport equation for the photons, which is known to be accurate in the multiple scattering regime investigated here. We determine the power spectrum of the atom density fluctuations, which displays an unusual $\sim k^{-4}$ scaling, and entails a complex underlying turbulent dynamics resulting from the formation of dynamical bubble-like structures. We derive a power spectrum from the theoretical photon bubble model which, to a high level of accuracy, explains the observations. The experimental results reported here, along with the theoretical model we developed may shed light on the analogue photon bubble instabilities in astrophysical scenarios.

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J. Rodrigues, J. Rodrigues, A. Ferreira, et. al.
Thu, 28 Apr 16
57/57

Comments: 5 pages

Ultraviolet emission lines of Si II in quasars — investigating the "Si II disaster" [GA]

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http://arxiv.org/abs/1604.07364


The observed line intensity ratios of the Si II 1263 and 1307 \AA\ multiplets to that of Si II 1814\,\AA\ in the broad line region of quasars are both an order of magnitude larger than the theoretical values. This was first pointed out by Baldwin et al. (1996), who termed it the “Si II disaster”, and it has remained unresolved. We investigate the problem in the light of newly-published atomic data for Si II. Specifically, we perform broad line region calculations using several different atomic datasets within the CLOUDY modeling code under optically thick quasar cloud conditions. In addition, we test for selective pumping by the source photons or intrinsic galactic reddening as possible causes for the discrepancy, and also consider blending with other species. However, we find that none of the options investigated resolves the Si II disaster, with the potential exception of microturbulent velocity broadening and line blending. We find that a larger microturbulent velocity ($\sim 500 \rm \, kms^{-1}$) may solve the Si II disaster through continuum pumping and other effects. The CLOUDY models indicate strong blending of the Si II 1307 \AA\ multiplet with emission lines of O I, although the predicted degree of blending is incompatible with the observed 1263/1307 intensity ratios. Clearly, more work is required on the quasar modelling of not just the Si II lines but also nearby transitions (in particular those of O I) to fully investigate if blending may be responsible for the Si II disaster.

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S. Laha, F. Keenan, G. Ferland, et. al.
Tue, 26 Apr 16
3/61

Comments: Accepted for publication in ApJ

Dark matter scattering on electrons: Accurate calculations of atomic excitations and implications for the DAMA signal [CL]

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http://arxiv.org/abs/1604.04559


We revisit the WIMP-type dark matter scattering on electrons that results in atomic ionization, and can manifest itself in a variety of existing direct-detection experiments. Unlike the WIMP-nucleon scattering, where current experiments probe typical interaction strengths much smaller than the Fermi constant, the scattering on electrons requires a much stronger interaction to be detectable, which in turn requires new light force carriers. We account for such new forces explicitly, by introducing a mediator particle with scalar or vector couplings to dark matter and to electrons. We then perform state of the art numerical calculations of atomic ionization relevant to the existing experiments. Our goals are to consistently take into account the atomic physics aspect of the problem (e.g., the relativistic effects, which can be quite significant), and to scan the parameter space: the dark matter mass, the mediator mass, and the effective coupling strength, to see if there is any part of the parameter space that could potentially explain the DAMA modulation signal. While we find that the modulation fraction of all events with energy deposition above 2 keV in NaI can be quite significant, reaching ~50%, the relevant parts of the parameter space are excluded by the XENON10 and XENON100 experiments.

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B. Roberts, V. Dzuba, V. Flambaum, et. al.
Mon, 18 Apr 16
14/41

Comments: N/A

H, He-like recombination spectra I: $l$-changing collisions for hydrogen [GA]

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http://arxiv.org/abs/1604.03978


Hydrogen and helium emission lines in nebulae form by radiative recombination. This is a simple process which, in principle, can be described to very high precision. Ratios of He I and H I emission lines can be used to measure the He$^+$/H$^+$ abundance ratio to the same precision as the recombination rate coefficients. This paper investigates the controversy over the correct theory to describe dipole $l$-changing collisions ($nl\rightarrow nl’=l\pm 1$) between energy-degenerate states within an $n$-shell. The work of Pengelly & Seaton (1964) has, for half-a-century, been considered the definitive study which “solved” the problem. Recent work by Vrinceanu et al.(2012) recommended the use of rate coefficients from a semi-classical approximation which are nearly an order of magnitude smaller than those of Pengelly & Seaton (1964), with the result that significantly higher densities are needed for the $nl$ populations to come into local thermodynamic equilibrium.
Here, we compare predicted H~I emissivities from the two works and find widespread differences, of up to $\approx 10$%. This far exceeds the 1% precision required to obtain the primordial He/H abundance ratio from observations so as to constrain Big Bang cosmologies. We recommend using the rate coefficients of Pengelly & Seaton (1964) for $l$-changing collisions, to describe the H recombination spectrum, based-on their quantum mechanical representation of the long-range dipole interaction.

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F. Guzman, N. Badnell, R. Williams, et. al.
Fri, 15 Apr 16
14/51

Comments: 6 pages, 3 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

Plasma-screening effects on the electronic structure of multiply charged Al ions using Debye and ionsphere models [CL]

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http://arxiv.org/abs/1604.01735


We analyze atomic structures of plasma embedded aluminum (Al) atom and its ions in the weakly and strongly coupling regimes. The plasma screening effects in these atomic systems are accounted for using the Debye and ion sphere (IS) potentials for the weakly coupling and strongly coupling plasmas, respectively. Within the Debye model, special attention is given to investigate the spherical and non-spherical plasma-screening effects considering in the electron-electron interaction potential. The relativistic coupled-cluster (RCC) method has been employed to describe the relativistic and electronic correlation effects in the above atomic systems. The variation in the ionization potentials (IPs) and excitation energies (EEs) of the plasma embedded Al ions are presented. It is found that the atomic systems exhibit more stability when the exact screening effects are taken into account. It is also showed that in the presence of strongly coupled plasma environment, the highly ionized Al ions show blue and red shifts in the spectral lines of the transitions between the states with same and different principal quantum numbers, respectively. Comparison among the results obtained from the Debye and IS models are also carried out considering similar plasma conditions.

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M. Das, B. Sahoo and S. Pal
Thu, 7 Apr 16
32/51

Comments: 6 figures and 3 tables

Atomic clocks and dark-matter signatures [CL]

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http://arxiv.org/abs/1603.07001


Recent developments in searches for dark-matter candidates with atomic clocks are reviewed. The intended audience is the atomic clock community.

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A. Derevianko
Thu, 24 Mar 16
37/60

Comments: To appear in Journal of Physics: Conference Series (JPCS); 6 pages, 4 figures

Excitation and charge transfer in low-energy hydrogen atom collisions with neutral atoms: Theory, comparisons, and application to Ca [CL]

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http://arxiv.org/abs/1603.07097


A theoretical method for the estimation of cross sections and rates for excitation and charge transfer processes in low-energy hydrogen atom collisions with neutral atoms, based on an asymptotic two-electron model of ionic-covalent interactions in the neutral atom-hydrogen atom system, is presented. The calculation of potentials and non-adiabatic radial couplings using the method is demonstrated. The potentials are used together with the multi-channel Landau-Zener model to calculate cross sections and rate coefficients. The main feature of the method is that it employs asymptotically exact atomic wavefunctions, which can be determined from known atomic parameters. The method is applied to Li+H, Na+H, and Mg+H collisions, and the results compare well with existing detailed full-quantum calculations. The method is applied to the astrophysically important problem of Ca+H collisions, and rate coefficients are calculated for temperatures in the range 1000-20000 K.

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P. Barklem
Thu, 24 Mar 16
52/60

Comments: Accepted by Phys. Rev. A

Rovibrationally-Resolved Photodissociaton of SH$^+$ [EPA]

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http://arxiv.org/abs/1602.05430


Photodissociation cross sections for the SH$^+$ radical are computed from all rovibrational (RV) levels of the ground electronic state X$~^3\Sigma^-$ for wavelengths from threshold to 500~\AA. The five electronic transitions, $2~ ^3\Sigma^- \leftarrow$ X$~^3\Sigma^-$, $3~ ^3\Sigma^- \leftarrow$ X$~^3\Sigma^-$, $A~ ^3\Pi \leftarrow$ X$~^3\Sigma^-$, $2~ ^3\Pi \leftarrow$ X$~^3\Sigma^-$, and $3~ ^3\Pi \leftarrow$ X$~^3\Sigma^-$, are treated with a fully quantum-mechanical two-state model, {i.e. no non-adiabatic coupling between excited states was included in our work.}. The photodissociation calculations incorporate adiabatic potentials and transition dipole moment functions computed in the multireference configuration interaction approach along with the Davidson correction (MRCI+Q), but adjusted to match available experimental molecular data and asymptotic atomic limits. Local thermodynamic equilibrium (LTE) photodissociation cross sections were computed which assume a Boltzmann distribution of RV levels in the X$~^3\Sigma^-$ molecular state of the SH$^+$ cation. The LTE cross sections are presented for temperatures in the range 1000-10,000~K. Applications of the current photodissociation cross sections to interstellar gas, photon-dominated regions, and stellar atmospheres are briefly discussed.

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E. McMillan, G. Shen, J. McCann, et. al.
Thu, 18 Feb 16
25/44

Comments: 21 pages, 13 figures, 2 tables. Accepted in J Phys. B: At. Mol. Opt. Phys. for the special issue on Atomic and molecular data for astrophysics

Discovery of Rubidium, Cadmium, and Germanium Emission Lines in the Near-Infrared Spectra of Planetary Nebulae [SSA]

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http://arxiv.org/abs/1602.03188


We identify [Rb IV] 1.5973 and [Cd IV] 1.7204 micron emission lines in high-resolution (R=40,000) near-infrared spectra of the planetary nebulae (PNe) NGC 7027 and IC 5117, obtained with the IGRINS spectrometer on the 2.7-m telescope at McDonald Observatory. We also identify [Ge VI] 2.1930 $\mu$m in NGC 7027. Alternate identifications for these features are ruled out based on the absence of other multiplet members and/or transitions with the same upper levels. Ge, Rb, and Cd can be enriched in PNe by s-process nucleosynthesis during the asymptotic giant branch (AGB) stage of evolution. To determine ionic abundances, we calculate [Rb IV] collision strengths and use approximations for those of [Cd IV] and [Ge VI]. Our identification of [Rb IV] 1.5973 $\mu$m is supported by the agreement between Rb3+/H+ abundances found from this line and the 5759.55 A feature in NGC 7027. Elemental Rb, Cd, and Ge abundances are derived with ionization corrections based on similarities in ionization potential ranges between the detected ions and O and Ne ionization states. Our analysis indicates abundances 2-4 times solar for Rb and Cd in both nebulae. Ge is subsolar in NGC 7027, but its abundance is uncertain due to the large and uncertain ionization correction. The general consistency of the measured relative s-process enrichments with predictions from models appropriate for these PNe (2.0-2.5 M_sun, [Fe/H]= -0.37) demonstrates the potential of using PN compositions to test s-process nucleosynthesis models.

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N. Sterling, H. Dinerstein, K. Kaplan, et. al.
Thu, 11 Feb 16
7/51

Comments: 14 pages, 2 figures, accepted for publication in ApJ Letters

Collision strengths and transition probabilities for Co III forbidden lines [CL]

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http://arxiv.org/abs/1602.00712


In this paper we compute the collision strengths and their thermally-averaged Maxwellian values for electron transitions between the fifteen lowest levels of doubly-ionised cobalt, Co^{2+}, which give rise to forbidden emission lines in the visible and infrared region of spectrum. The calculations also include transition probabilities and predicted relative line emissivities. The data are particularly useful for analysing the thermodynamic conditions of supernova ejecta.

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P. Storey and T. Sochi
Wed, 3 Feb 16
33/54

Comments: 9 pages, 2 figures, 11 tables. arXiv admin note: text overlap with arXiv:1509.03164

Plasma code for astrophysical charge exchange emission at X-ray wavelengths [HEAP]

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http://arxiv.org/abs/1601.05958


Charge exchange X-ray emission provides unique insights into the interactions between cold and hot astrophysical plasmas. Besides its own profound science, this emission is also technically crucial to all observations in the X-ray band, since charge exchange with the solar wind often contributes a significant foreground component that contaminates the signal of interest. By approximating the cross sections resolved to $n$ and $l$ atomic subshells, and carrying out complete radiative cascade calculation, we create a new spectral code to evaluate the charge exchange emission in the X-ray band. Comparing to collisional thermal emission, charge exchange radiation exhibits enhanced lines from large-$n$ shells to the ground, as well as large forbidden-to-resonance ratios of triplet transitions. Our new model successfully reproduces an observed high-quality spectrum of comet C/2000 WM1 (LINEAR), which emits purely by charge exchange between solar wind ions and cometary neutrals. It demonstrates that a proper charge exchange model will allow us to probe remotely the ion properties, including charge state, dynamics, and composition, at the interface between the cold and hot plasmas.

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L. Gu, J. Kaastra and A. Raassen
Mon, 25 Jan 16
34/56

Comments: Accepted for publication in Astronomy & Astrophysics

Solar opacity calculations using the super-transition-array method [SSA]

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http://arxiv.org/abs/1601.01930


An opacity model based on the Super-Transition-Array (STA) method for the calculation of monochromatic opacities of local thermodynamic equilibrium plasmas was developed. The model is described and used to calculate spectral opacities for a solar model implementing the recent AGSS09 composition. Calculations are carried throughout the solar radiative zone. The relative contributions of different chemical elements and photon-matter processes to the total Rosseland mean opacity are analyzed in detail. Monochromatic opacities and charge state distributions were compared with the widely used Opacity-Project (OP) code, for several elements near the radiation-convection interface. STA Rosseland opacities for the solar mixture show a very good agreement with OP and the OPAL opacity code, throughout the radiation zone. Finally, an explicit STA calculation of the full AGSS09 photospheric mixture, including all heavy metals was performed. It was shown that due to their extremely low abundance, and despite being very good photon absorbers, the heavy elements do not affect the Rosseland opacity.

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M. Krief, A. Feigel and D. Gazit
Mon, 11 Jan 16
6/57

Comments: 15 pages, 28 figures

Multipole Traps as Tools in Environmental Studies [CL]

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http://arxiv.org/abs/1512.05522


Trapping of microparticles, nanoparticles and aerosols is an issue of major interest for physics and chemistry. We present a setup intended for microparticle trapping in multipole linear Paul trap geometries, operating under Standard Ambient Temperature and Pressure (SATP) conditions. A 16-electrode linear trap geometry has been designed and tested, with an aim to confine a larger number of particles with respect to quadrupole traps and thus enhance the signal to noise ratio, as well as to study microparticle dynamical stability in electrodynamic fields. Experimental tests and numerical simulations suggest that multipole traps are very suited for high precision mass spectrometry measurements in case of different microparticle species or to identify the presence of certain aerosols and polluting agents in the atmosphere. Particle traps represent versatile tools for environment monitoring or for the study of many-body Coulomb systems and dusty plasmas.

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B. Mihalcea, C. Stan, L. Giurgiu, et. al.
Fri, 18 Dec 15
13/70

Comments: 17 pages, 8 figures

Multipole Electrodynamic Ion Trap Geometries for Microparticle Confinement under Standard Ambient Temperature and Pressure Conditions [CL]

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http://arxiv.org/abs/1512.05503


Trapping of microparticles and aerosols is of great interest for physics and chemistry. We report microparticle trapping in multipole linear Paul trap geometries, operating under Standard Ambient Temperature and Pressure (SATP) conditions. An 8-electrode and a 12-electrode linear trap geometries have been designed and tested with an aim to achieve trapping for larger number of particles and to study microparticle dynamical stability in electrodynamic fields. We report emergence of planar and volume ordered structures of the microparticles, depending on the a.c. trapping frequency and particle specific charge ratio. The electric potential within the trap was mapped using the electrolytic tank method. Particle dynamics was simulated using a stochastic Langevin equation. We emphasize extended regions of stable trapping with respect to quadrupole traps, as well as good agreement between experiment and numerical simulations.

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B. Mihalcea, L. Giurgiu, C. Stan, et. al.
Fri, 18 Dec 15
21/70

Comments: 24 pages, 11 figures

Importance of the completeness of the configuration interaction and close coupling expansions in R-matrix calculations for highly-charged ions: electron-impact excitation of Fe $^{20+}$ [CL]

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http://arxiv.org/abs/1511.05776


We have carried-out two intermediate coupling frame transformation (ICFT) R-matrix calculations for the electron-impact excitation of C-like Fe $^{20+}$, both of which use the same expansions for their configuration interaction (CI) and close-coupling (CC) representations. The first expansion arises from the configurations 2s$^2$ 2p$^2$, 2s 2p$^3$, 2p$^4$, {2s$^2$ 2p, 2s 2p$^2$, 2p$^3$} nl, with n=3,4, for l=0-3, which give rise to 564 CI/CC levels. The second adds configurations 2s$^2$ 2p 5l, for l=0-2, which give rise to 590 CI/CC levels in total. Comparison of oscillator strengths and effective collision strengths from these two calculations demonstrates the lack of convergence in data for n=4 from the smaller one. Comparison of results for the 564 CI/CC level calculation with an earlier ICFT R-matrix calculation which used the exact same CI expansion but truncated the CC expansion to only 200 levels demonstrates the lack of convergence of the earlier data, particularly for n=3 levels. Also, we find that the results of our 590 CC R-matrix calculation are significantly and systematically larger than those of an earlier comparable Distorted Wave-plus-resonances calculation. Thus, it is important still to take note of the (lack of) convergence in both atomic structural and collisional data, even in such a highly-charged ion as Fe $^{20+}$, and to treat resonances non-perturbatively. This is of particular importance for Fe ions given their importance in the spectroscopic diagnostic modelling of astrophysical plasmas.

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L. Fernandez-Menchero, A. Giunta, G. Zanna, et. al.
Thu, 19 Nov 15
11/73

Comments: 17 pages, 6 tables, 26 figures, 38 bibliographic references. Pac numbers 34.50.Fa, 52.20.Fs, 95.30.Ky

Searching for Scalar Dark Matter in Atoms and Astrophysical Phenomena: Variation of Fundamental Constants [CL]

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http://arxiv.org/abs/1511.04100


We propose to search for scalar dark matter via its effects on the electromagnetic fine-structure constant and particle masses. Scalar dark matter that forms an oscillating classical field produces `slow’ linear-in-time drifts and oscillating variations of the fundamental constants, while scalar dark matter that forms topological defects produces transient-in-time variations of the constants of Nature. These variations can be sought for with atomic clock, laser interferometer and pulsar timing measurements. Atomic spectroscopy and Big Bang nucleosynthesis measurements already give improved bounds on the quadratic interaction parameters of scalar dark matter with the photon, electron, and light quarks by up to 15 orders of magnitude, while Big Bang nucleosynthesis measurements provide the first such constraints on the interaction parameters of scalar dark matter with the massive vector bosons.

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Y. Stadnik, B. Roberts, V. Flambaum, et. al.
Mon, 16 Nov 15
22/57

Comments: 4 pages, 1 figure, Contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs, Zaragoza, June 22 to 26, 2015

On highly accurate computations of some properties of the negatively charged positronium and hydrogen ions [CL]

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http://arxiv.org/abs/1511.02157


Numerical values of some important electron-positron and electron-electron expectation values are reported for the ground (bound) $1^1S-$state of the negatively charged Ps$^{-}$ and H$^{-}$ ions. Convergence of these values upon the total number of basis functions $N$ used is briefly discussed.

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A. Frolov
Mon, 9 Nov 15
42/55

Comments: N/A

Photodetachment cross-section of the negatively charged hydrogen ion [SSA]

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http://arxiv.org/abs/1510.04766


Photodetachment cross-section $\sigma_{ph}(p_e)$ of the negatively charged hydrogen ion H$^{-}$ is determined with the use of highly accurate variational wave functions constructed for this ion. Photodetachment cross-sections of the H$^{-}$ ion are also studied for very small and very large values of the photo-electron momentum $p_e$. Maximum of this cross-section has been evaluated to very high accuracy and we have found that $[\sigma_{ph}(p_e)]_{\max} \approx$ 3.8627035742 $\cdot 10^{-17}$ $cm^2$ at $p_e \approx$ 0.113206(1) $a.u.$ Photodetachment of the H$^{-}$ ion at very small and very large $p_e$ values is also considered. Our method is based upon the Rayleigh’s formula for spherical Bessel functions.

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A. Frolov
Mon, 19 Oct 15
29/44

Comments: arXiv admin note: substantial text overlap with arXiv:1505.00004

Ionization of atoms by slow heavy particles [CL]

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http://arxiv.org/abs/1509.09044


Atoms and molecules can become ionized during the scattering of a slow, heavy particle off a bound electron. Such an interaction involving leptophilic weakly interacting massive particles (WIMPs) is a promising possible explanation for the anomalous 9 sigma annual modulation in the DAMA dark matter direct detection experiment [R. Bernabei et al., Eur. Phys. J. C 73, 2648 (2013)]. We demonstrate the applicability of the Born approximation for such an interaction by showing its equivalence to the semiclassical adiabatic treatment of atomic ionization by slow-moving WIMPs. Conventional wisdom has it that the ionization probability for such a process should be exponentially small. We show, however, that due to nonanalytic, cusp-like behaviour of Coulomb functions close to the nucleus this suppression is removed, leading to an effective atomic structure enhancement. We also show that electron relativistic effects actually give the dominant contribution to such a process, meaning that nonrelativistic calculations may greatly underestimate the cross section.

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B. Roberts, V. Flambaum and G. Gribakin
Thu, 1 Oct 15
61/63

Comments: 5 pages, 2 figures

Energy levels and radiative rates for transitions in Cr-like Co IV and Ni V [CL]

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http://arxiv.org/abs/1509.07648


We report calculations of energy levels and radiative rates ($A$-values) for transitions in Cr-like Co IV and Ni V. The quasi-relativistic Hartree-Fock (QRHF) code is adopted for calculating the data although GRASP (general-purpose relativistic atomic structure package) and flexible atomic code (FAC) have also been employed for comparison purposes. No radiative rates are available in the literature to compare with our results, but our calculated energies are in close agreement with those compiled by NIST for a majority of the levels. However, there are discrepancies for a few levels of up to 3\%. The $A$-values are listed for all significantly contributing E1, E2 and M1 transitions, and the corresponding lifetimes reported, although unfortunately no previous theoretical or experimental results exist to compare with our data.

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K. Aggarwal, P. Bogdanovich, R. Karpuskiene, et. al.
Mon, 28 Sep 15
47/67

Comments: The paper will appear in ADNDT (2016) and in October 2015 on the web

On the gravitational quantum states of helium atoms in the gravitational field of a cold neutron star [HEAP]

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http://arxiv.org/abs/1509.06600


A study of gravitational properties of matter presents a fundamental interest. The possibility of investigation of quantum gravitational states of matter by the example of helium atom is shown. The capability of the existence of helium quantum states in the gravitational field of a cold neutron star is examined. Observation of such states is done with the help of rotating neutron star’s magnetic field. Periodically changing magnetic field induces transitions between gravitational states of helium atom and leads to the appearance of gravitational transitions’ spectral lines in gigahertz frequency range.

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O. Dalkarov and E. Kupriyanova
Wed, 23 Sep 15
15/63

Comments: proceedings of The 34th International Cosmic Ray Conference (ICRC 2015), 8 pages, 3 figures

The FERRUM project: Experimental lifetimes and transition probabilities from highly excited even 4d levels in Fe ii [SSA]

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http://arxiv.org/abs/1509.06155


We report lifetime measurements of the 6 levels in the 3d6(5D)4d e6G term in Fe ii at an energy of 10.4 eV, and f -values for 14 transitions from the investigated levels. The lifetimes were measured using time-resolved laser-induced fluorescence on ions in a laser-produced plasma. The high excitation energy, and the fact that the levels have the same parity as the the low-lying states directly populated in the plasma, necessitated the use of a two-photon excitation scheme. The probability for this process is greatly enhanced by the presence of the 3d6(5D)4p z6F levels at roughly half the energy di?erence. The f -values are obtained by combining the experimental lifetimes with branching fractions derived using relative intensities from a hollow cathode discharge lamp recorded with a Fourier transform spectrometer. The data is important for benchmarking atomic calculations of astrophysically important quantities and useful for spectroscopy of hot stars.

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H. Hartman, H. Nilsson, L. Engstrom, et. al.
Tue, 22 Sep 15
72/77

Comments: A&A, accepted

Collision strengths and transition probabilities for Co II infrared forbidden lines [CL]

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http://arxiv.org/abs/1509.03164


We calculate collision strengths and their thermally-averaged Maxwellian values for electron excitation and de-excitation between the fifteen lowest levels of singly-ionised cobalt, Co+, which give rise to emission lines in the near- and mid-infrared. Transition probabilities are also calculated and relative line intensities predicted for conditions typical of supernova ejecta. The diagnostic potential of the 10.52, 15.46 and 14.74 micro-metre transition lines is briefly discussed.

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P. Storey, C. Zeippen and T. Sochi
Fri, 11 Sep 15
12/54

Comments: 9 pages, 4 figures, 7 tables

Manifestations of dark matter and variations of fundamental constants in atoms and astrophysical phenomena [CL]

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http://arxiv.org/abs/1509.00966


We present an overview of recent developments in the detection of light bosonic dark matter, including axion, pseudoscalar axion-like and scalar dark matter, which form either a coherently oscillating classical field or topological defects (solitons). We emphasise new high-precision laboratory and astrophysical measurements, in which the sought effects are linear in the underlying interaction strength between dark matter and ordinary matter, in contrast to traditional detection schemes for dark matter, where the effects are quadratic or higher order in the underlying interaction parameters and are extremely small. New terrestrial experiments include measurements with atomic clocks, spectroscopy, atomic and solid-state magnetometry, torsion pendula, ultracold neutrons, and laser interferometry. New astrophysical observations include pulsar timing, cosmic radiation lensing, Big Bang nucleosynthesis and cosmic microwave background measurements. We also discuss various recently proposed mechanisms for the induction of slow `drifts’, oscillating variations and transient-in-time variations of the fundamental constants of Nature by dark matter, which offer a more natural means of producing a cosmological evolution of the fundamental constants compared with traditional dark energy-type theories, which invoke a (nearly) massless underlying field. Thus, measurements of variation of the fundamental constants gives us a new tool in dark matter searches.

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Y. Stadnik and V. Flambaum
Fri, 4 Sep 15
12/58

Comments: 32 pages, 10 figures, Invited book review for the book `Indirect Effects of Dark Matter Physics’, edited by Maxim Yu. Khlopov, World Scientific, 2016. ISBN: 978-981-4635-74-5

CHIANTI – An atomic database for Emission Lines. Version 8 [SSA]

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http://arxiv.org/abs/1508.07631


We present version 8 of the CHIANTI database. This version includes a large amount of new data and ions, which represent a significant improvement in the soft X-ray, EUV and UV spectral regions, which several space missions currently cover. New data for neutrals and low charge states are also added. The data are assessed, but to improve the modelling of low-temperature plasma the effective collision strengths for most of the new datasets are not spline-fitted as previously, but are retained as calculated. This required a change of the format of the CHIANTI electron excitation files. The format of the energy files has also been changed. Excitation rates between all the levels are retained for most of the new datasets, so the data can in principle be used to model high-density plasma. In addition, the method for computing the differential emission measure used in the CHIANTI software has been changed.

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G. Zanna, K. Dere, P. Young, et. al.
Tue, 1 Sep 15
9/82

Comments: Accepted for publication in Astronomy & Astrophysics

Merged-beams Reaction Studies of O + H_3^+ [IMA]

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http://arxiv.org/abs/1508.07882


We have measured the reaction of O + H3+ forming OH+ and H2O+. This is one of the key gas-phase astrochemical processes initiating the formation of water molecules in dense molecular clouds. For this work, we have used a novel merged fast-beams apparatus which overlaps a beam of H3+ onto a beam of ground-term neutral O. Here, we present cross section data for forming OH+ and H2O+ at relative energies from \approx 3.5 meV to \approx 15.5 and 0.13 eV, respectively. Measurements were performed for statistically populated O(3PJ) in the ground term reacting with hot H3+ (with an internal temperature of \approx 2500-3000 K). From these data, we have derived rate coefficients for translational temperatures from \approx 25 K to \approx 10^5 and 10^3 K, respectively. Using state-of-the-art theoretical methods as a guide, we have converted these results to a thermal rate coefficient for forming either OH+ or H2O+, thereby accounting for the temperature dependence of the O fine-structure levels. Our results are in good agreement with two independent flowing afterglow measurements at a temperature of \approx 300 K, and with a corresponding level of H3+ internal excitation. This good agreement strongly suggests that the internal excitation of the H3+ does not play a significant role in this reaction. The Langevin rate coefficient is in reasonable agreement with the experimental results at 10 K but a factor of \approx 2 larger at 300 K. The two published classical trajectory studies using quantum mechanical potential energy surfaces lie a factor of \approx 1.5 above our experimental results over this 10-300 K range.

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N. Ruette, K. Miller, A. OConnor, et. al.
Tue, 1 Sep 15
11/82

Comments: 43 pages, 11 figures. Submitted to the Astrophysical Journal

State of the art for ab initio vs empirical potentials for predicting 6e$^{-}$ excited state molecular energies: Application to Li$_{2}\left(b,1^{3}Π_{u}\right)$ [CL]

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http://arxiv.org/abs/1508.07184


We build the first analytic empirical potential for the most deeply bound $\mbox{Li}_{2}$ state: $b\left(1^{3}\Pi_{u}\right)$. Our potential is based on experimental energy transitions covering $v=0-34$, and very high precision theoretical long-range constants. It provides high accuracy predictions up to $v=100$ which pave the way for high-precision long-range measurements, and hopefully an eventual resolution of the age old discrepancy between experiment and theory for the $\mbox{Li}\left(2^{2}S\right)+\mbox{Li}\left(2^{2}P\right)$ $C_{3}$ value. State of the art ab initio calculations predict vibrational energy spacings that are all in at most 0.8 cm$^{-1}$ disagreement with the empirical potential.

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N. Dattani and R. Roy
Mon, 31 Aug 15
28/63

Comments: Feedback encouraged. 16 pages, 3 figures

A unified numerical model of collisional depolarization and broadening rates due to hydrogen atom collisions [SSA]

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http://arxiv.org/abs/1508.06482


Interpretation of solar polarization spectra accounting for partial or complete frequency redistribution requires data on various collisional processes. Data for depolarization and polarization transfer are needed but often missing, while data for collisional broadening are usually more readily available. Recent work by Sahal-Br\’echot and Bommier concluded that despite underlying similarities in the physics of collisional broadening and depolarization processes, relationships between them are not possible to derive purely analytically.
We aim to derive accurate numerical relationships between the collisional broadening rates and the collisional depolarization and polarization transfer rates due to hydrogen atom collisions. Such relationships would enable accurate and efficient estimation of collisional data for solar applications.
Using earlier results for broadening and depolarization processes based on general (i.e. not specific to a given atom), semi-classical calculations employing interaction potentials from perturbation theory, genetic programming (GP) has been used to fit the available data and generate analytical functions describing the relationships between them. The predicted relationships from the GP-based model are compared with the original data to estimate the accuracy of the method.

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M. Derouich, A. Radi and P. Barklem
Thu, 27 Aug 15
63/71

Comments: 10 pages, 7 figures, Accepted for publication in Astronomy & Astrophysics

Comment on "Axion induced oscillating electric dipole moments" [CL]

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http://arxiv.org/abs/1507.05265


In the recent work of Hill [Phys. Rev. D 91, 111702(R) (2015)], it is claimed that the axion electromagnetic anomaly induces an oscillating electron electric dipole moment of frequency $m_a$ and strength $\sim 10^{-32}~e$ cm, in the limit $v/c \to 0$ for the axion field. Here, we demonstrate that a proper treatment of this problem in the lowest order yields no electric dipole moment of the electron in the same limit.

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V. Flambaum, B. Roberts and Y. Stadnik
Tue, 21 Jul 15
7/74

Comments: 2 pages

Storage Ring Cross Section Measurements for Electron Impact Ionization of Fe 7+ [CL]

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http://arxiv.org/abs/1507.04216


We have measured electron impact ionization (EII) for Fe 7+ from the ionization threshold up to 1200 eV. The measurements were performed using the TSR heavy ion storage ring. The ions were stored long enough prior to measurement to remove most metastables, resulting in a beam of 94% ground state ions. Comparing with the previously recommended atomic data, we find that the Arnaud & Raymond (1992) cross section is up to about 40\% larger than our measurement, with the largest discrepancies below about 400~eV. The cross section of Dere (2007) agrees to within 10%, which is about the magnitude of the experimental uncertainties. The remaining discrepancies between measurement and the most recent theory are likely due to shortcomings in the theoretical treatment of the excitation-autoionization contribution.

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M. Hahn, A. Becker, D. Bernhardt, et. al.
Thu, 16 Jul 15
18/61

Comments: Submitted to the Astrophysical Journal

Reply to comment on "Searching for Topological Defect Dark Matter via Nongravitational Signatures" [CL]

Posted on by

http://arxiv.org/abs/1507.01375


In the comment of Avelino, Sousa and Lobo [arXiv:1506.06028], it is claimed that networks of topological defects cannot be the origin of the pulsar glitch phenomenon. Here, we point out that topological defects may trigger pulsar glitches within traditional scenarios, such as vortex unpinning and crustal fracture, in which the source of angular momentum required for a glitch event is provided by the pulsar itself.

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Y. Stadnik and V. Flambaum
Tue, 7 Jul 15
58/65

Comments: 2 pages

New generation low-energy probes for ultralight axion and scalar dark matter [CL]

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http://arxiv.org/abs/1506.08364


We present a brief overview of a new generation of high-precision laboratory and astrophysical measurements to search for ultralight (sub-eV) axion, axion-like pseudoscalar and scalar dark matter, which form either a coherent condensate or topological defects (solitons). In these new detection methods, the sought effects are linear in the interaction constant between dark matter and ordinary matter, which is in stark contrast to traditional searches for dark matter, where the sought effects are quadratic or higher order in the underlying interaction constants (which are extremely small).

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Y. Stadnik and V. Flambaum
Tue, 30 Jun 15
38/75

Comments: 10 pages, Invited brief review for Modern Physics Letters A, Guest Editor: Maxim Yu. Khlopov

Bound state properties and photodetachment of the negatively charged hydrogen ions [SSA]

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http://arxiv.org/abs/1505.07859


Absorption of infrared and visible radiation from stellar emission spectra by the negatively charged hydrogen ions H$^{-}$ is considered. The explicit formula for the photodetachment cross-section of the negatively charged hydrogen ion(s) is derived. Photodetachemnt cross-sections of the ${}^{\infty}$H$^{-}$, ${}^{3}$H$^{-}$ (or T$^{-}$), ${}^{2}$H$^{-}$ (or D$^{-}$) and ${}^{1}$H$^{-}$ ions are determined to high accuracy and for a large number of photo-electron momenta/energies. We introduce criteria which can be used to evaluate the overall quality of highly accurate wave functions of the hydrogen ion(s). One of these criteria is based on highly accurate calculations of the lowest order QED corrections in the negatively charged hydrogen ions, including ${}^{1}$H$^{-}$ (protium), ${}^{2}$H$^{-}$ (deuterium), ${}^{3}$H$^{-}$ (tritium) and model ion with the infinitely heavy nucleus ${}^{\infty}$H$^{-}$. An effective approach has been developed to calculate three-body integrals with the Bessel functions of different orders. Some preliminary evaluations of the phototdetachment cross-sections of the negatively charged hydrogen ions are performed. Inverse bremsstrahlung in the field of the neutral hydrogen atom is briefly discussed.

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A. Frolov
Mon, 1 Jun 15
23/62

Comments: arXiv admin note: substantial text overlap with arXiv:1110.3432

Accurate Prediction of the Ammonia Probes of a Variable Proton-to-Electron Mass Ratio [CEA]

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http://arxiv.org/abs/1505.05989


A comprehensive study of the mass sensitivity of the vibration-rotation-inversion transitions of $^{14}$NH$_3$, $^{15}$NH$_3$, $^{14}$ND$_3$, and $^{15}$ND$_3$ is carried out variationally using the TROVE approach. Variational calculations are robust and accurate, offering a new way to compute sensitivity coefficients. Particular attention is paid to the $\Delta k=\pm 3$ transitions between the accidentally coinciding rotation-inversion energy levels of the $\nu_2=0^+,0^-,1^+$ and $1^-$ states, and the inversion transitions in the $\nu_4=1$ state affected by the “giant” $l$-type doubling effect. These transitions exhibit highly anomalous sensitivities, thus appearing as promising probes of a possible cosmological variation of the proton-to-electron mass ratio $\mu$. Moreover, a simultaneous comparison of the calculated sensitivities reveals a sizeable isotopic dependence which could aid an exclusive ammonia detection.

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A. Owens, S. Yurchenko, W. Thiel, et. al.
Mon, 25 May 15
37/47

Comments: 18 pages, 2 figures, 10 tables

The Abundances of Light Neutron-Capture Elements in Planetary Nebulae III. The Impact of New Atomic Data on Nebular Selenium and Krypton Abundance Determinations [SSA]

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http://arxiv.org/abs/1505.01162


The detection of neutron(n)-capture elements in several planetary nebulae (PNe) has provided a new means of investigating s-process nucleosynthesis in low-mass stars. However, a lack of atomic data has inhibited accurate trans-iron element abundance determinations in astrophysical nebulae. Recently, photoionization and recombination data were determined for Se and Kr, the two most widely detected n-capture elements in nebular spectra. We have incorporated these new data into the photoionization code Cloudy. To test the atomic data, numerical models were computed for 15 PNe that exhibit emission lines from multiple Kr ions. We found systematic discrepancies between the predicted and observed emission lines that are most likely caused by inaccurate photoionization and recombination data. These discrepancies were removed by adjusting the Kr$^+$–Kr$^{3+}$ photoionization cross sections within their cited uncertainties and the dielectronic recombination rate coefficients by slightly larger amounts. From grids of models spanning the physical conditions encountered in PNe, we derive new, broadly applicable ionization correction factor (ICF) formulae for calculating Se and Kr elemental abundances. The ICFs were applied to our previous survey of near-infrared [Kr III] and [Se IV] emission lines in 120 PNe. The revised Se and Kr abundances are 0.1-0.3 dex lower than former estimates, with average values of [Se/(O, Ar)]=0.12$\pm$0.27 and [Kr/(O, Ar)]=0.82$\pm$0.29, but correlations previously found between their abundances and other nebular and stellar properties are unaffected. We also find a tendency for high-velocity PNe that can be associated with the Galactic thick disk to exhibit larger s-process enrichments than low-velocity PNe belonging to the thin disk population.

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N. Sterling, R. Porter and H. Dinerstein
Thu, 7 May 15
44/50

Comments: 73 pages, 6 figures, 18 tables, accepted for publication in ApJS

Constraining scalar dark matter with Big Bang nucleosynthesis and atomic spectroscopy [CEA]

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http://arxiv.org/abs/1504.01798


Scalar dark matter can interact with Standard Model (SM) particles, altering the fundamental constants of Nature in the process. Changes in the fundamental constants during and before Big Bang nucleosynthesis (BBN) produce changes in the primordial abundances of the light elements. In particular, the primordial abundance of $^{4}$He is predominantly determined by the ratio of the neutron-proton mass difference to freeze-out temperature at the time of the weak interaction freeze-out prior to BBN, which is a sensitive function of the fundamental constants. By comparing the measured and calculated (within the SM) primordial abundance of $^{4}$He, we are able to derive stringent constraints on the mass of a scalar dark matter particle $\phi$ together with its interactions with photons, light quarks and massive vector bosons via linear and quadratic couplings in $\phi$. We also derive constraints on the quadratic interaction of $\phi$ with photons from recent atomic dysprosium spectroscopy measurements.

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Y. Stadnik and V. Flambaum
Thu, 9 Apr 15
38/52

Comments: 6 pages, 6 figures. arXiv admin note: text overlap with arXiv:1503.08540

Can dark matter induce cosmological evolution of the fundamental constants of Nature? [CEA]

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http://arxiv.org/abs/1503.08540


Traditional theories, which predict the cosmological evolution of the fundamental constants of Nature, assume that the underlying fields, which give rise to this evolution, are unnaturally light. We demonstrate that massive fields, such as dark matter, also directly produce a cosmological evolution of the fundamental constants. We consider the specific model of a scalar dark matter field $\phi$, which interacts with Standard Model particles via quadratic couplings in $\phi$. In this particular model, cosmological evolution of the fundamental constants arises due to changes in $\left<\phi^2\right>$ in time and space. The most stringent constraints on the physical parameters of the present model come from measurements of the neutron-proton mass difference at the time of the weak interaction freeze-out.

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Y. Stadnik and V. Flambaum
Tue, 31 Mar 15
67/71

Comments: 4 pages

Energy levels, radiative rates and electron impact excitation rates for transitions in C III [SSA]

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http://arxiv.org/abs/1503.07673


We report energy levels, radiative rates (A-values) and lifetimes for the astrophysically-important Be-like ion C III. For the calculations, 166 levels belonging to the $n \le$ 5 configurations are considered and the {\sc grasp} (General-purpose Relativistic Atomic Structure Package) is adopted. Einstein A-coefficients are provided for all E1, E2, M1 and M2 transitions, while lifetimes are compared with available measurements as well as theoretical results, and no large discrepancies noted. Our energy levels are assessed to be accurate to better than 1\% for a majority of levels, and A-values to better than 20\% for most transitions. Collision strengths are also calculated, for which the Dirac Atomic R-matrix Code ({\sc darc}) is used. A wide energy range, up to 21 Ryd, is considered and resonances resolved in a fine energy mesh in the thresholds region. The collision strengths are subsequently averaged over a Maxwellian velocity distribution to determine effective collision strengths up to a temperature of 8.0$\times$10$^5$ K, sufficient for most astrophysical applications. Our data are compared with the recent $R$-matrix calculations of Fern{\’a}ndez-Menchero, Del Zanna \& Badnell [A\&A 566 (2014) A104], and significant differences (up to over an order of magnitude) are noted for several transitions over the complete temperature range of the results.

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K. Aggarwal and F. Keenan
Fri, 27 Mar 15
37/55

Comments: 16 pages including 9 Tables and 3 Figures, will appear in MNRAS (2015)

Validity of the ICFT R-matrix method: Be-like Al$^{9+}$ a case study [IMA]

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http://arxiv.org/abs/1503.04980


We have carried-out 98-level configuration-interaction / close-coupling (CI/CC) intermediate coupling frame transformation (ICFT) and Breit-Pauli R-matrix calculations for the electron-impact excitation of Be-like Al$^{9+}$. The close agreement that we find between the two sets of effective collision strengths demonstrates the continued robustness of the ICFT method. On the other hand, a comparison of this data with previous 238-level CI/CC ICFT effective collision strengths shows that the results for excitation up to n=4 levels are systematically and increasingly underestimated over a wide range of temperatures by R-matrix calculations whose close-coupling expansion extends only to n=4 (98-levels). Thus, we find to be false a recent conjecture that the ICFT approach may not be completely robust. The conjecture was based upon a comparison of 98-level CI/CC Dirac R-matrix effective collision strengths for Al$^{9+}$ with those from the 238-level CI/CC ICFT R-matrix calculations. The disagreement found recently is due to a lack of convergence of the close-coupling expansion in the 98-level CI/CC Dirac work. The earlier 238-level CI/CC ICFT work has a superior target to the 98-level CI/CC Dirac one and provides more accurate atomic data. Similar considerations need to be made for other Be-like ions and for other sequences.

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L. Fernandez-Menchero, G. Zanna and N. Badnell
Wed, 18 Mar 15
39/59

Comments: 10 pages, 12 color online figures, 4 tables, 27 references. Submitted to MNRAS