Two-Electron-One-Photon Processes Can Dominate over Allowed Radiative and Auger Decay in Few-Electron Ions [CL]

http://arxiv.org/abs/2003.05965


We resonantly excite the $K$ series of O$^{5+}$ and O$^{6+}$ up to principal quantum number $n=11$ with monochromatic x rays, producing $K$-shell holes, and observe their relaxation by soft x-ray emission. Some photoabsorption resonances of O$^{5+}$ reveal strong two-electron-one-photon (TEOP) transitions. We find that for the $1s\,2s\,5p\, ^1P_1$ state, TEOP relaxation is by far stronger than the competing, and usually much faster, allowed Auger and radiative decay paths. This enhanced TEOP decay arises from a strong correlation with the near-degenerate upper state $1s\,2p\,4s\, ^1P_1$ of a $K\alpha$ satellite. Even in three-electron systems, TEOP transitions can play a dominant role, and the present results should guide further research on the ubiquitous and abundant many-electron ions where various electronic energy degeneracies and level mixings are far more common.

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M. Togawa, S. Kühn, C. Shah, et. al.
Mon, 16 Mar 20
45/57

Comments: 8 pages, 6 figures (incl. Supplement Materia) submitted to PRL

H–He collision-induced satellite in the Lyman-$α$ profile of DBA white dwarf stars [SSA]

http://arxiv.org/abs/2003.05110


The spectra of helium-dominated white dwarf stars with hydrogen in their atmosphere present a distinctive broad feature centered around 1160~\AA\/ in the blue wing of the Lyman-$\alpha$ line. It is extremely apparent in WD 1425+540 recently observed with HST COS. With new theoretical line profiles based on ab initio atomic interaction potentials we show that this feature is a signature of a collision-induced satellite due to an asymptotically forbidden transition. This quasi-molecular spectral satellite is crucial to understanding the asymmetrical shape of Lyman-$\alpha$ seen in this and other white dwarf spectra. Our previous work predicting this absorption feature was limited by molecular potentials that were not adequate to follow the atomic interactions with spectroscopic precision to the asymptotic limit of large separation. A new set of potential energy curves and electronic dipole transition moments for the lowest electronic states of the H–He system were developed to account accurately for the behavior of the atomic interactions at all distances, from the chemical regime within 1~\AA\/ out to where the radiating H atoms are not significantly perturbed by their neighbors. We use a general unified theory of collision-broadened atomic spectral lines to describe a rigorous treatment of hydrogen Lyman-$\alpha$ with these potentials and present a new study of its broadening by radiative collisions of hydrogen and neutral helium. These results enable ab initio modeling of radiative transport in DBA white dwarf atmospheres.

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N. Allard, J. Kielkopf, S. Xu, et. al.
Thu, 12 Mar 20
23/49

Comments: 9 pages, 7 figures

Charge exchange, from the sky to the laboratory: A method to determine state-selective cross-sections for improved modeling [HEAP]

http://arxiv.org/abs/2003.04316


Charge exchange (CX) is a semi-resonant recombination process that can lead to spectral line emission in the X-ray band. It occurs in nearly any environment where hot plasma and cold gas interact: in the solar system, in comets and planetary atmospheres, and likely astrophysically, in, for example, supernova remnants and galaxy clusters. It also contributes to the soft X-ray background. Accurate spectral modeling of CX is thus critical to properly interpreting our astrophysical observations, but the commonly used CX models in popular spectral fitting packages often rely on scaling equations and may not accurately describe observations or laboratory measurements. This paper introduces a method that can be applied to high-resolution CX spectra to directly extract state-selective CX cross-sections for electron capture, a key parameter for properly simulating the resulting CX spectrum.

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G. Betancourt-Martinez, R. Cumbee and M. Leutenegger
Wed, 11 Mar 20
62/65

Comments: 6 pages, 6 figures

Large-scale multiconfiguration Dirac-Hartree-Fock calculations for astrophysics: n=4 levels in P-like ions from Mn~XI to Ni~XIV [CL]

http://arxiv.org/abs/2003.00121


Using the multiconfiguration Dirac-Hartree-Fock and the relativistic configuration interaction methods, a consistent set of transition energies and radiative transition data for the lowest 546 (623, 701, 745) states of the $3p^4 3d$, $3s 3p^2 3d^2$, $3s 3p^3 4p$, $3s 3p^4$, $3s^2 3d^3$, $3s^2 3p^2 3d$, $3s^2 3p^2 4d$, $3s^2 3p^2 4s$, $3p^3 3d^2$, $3p^5$, $3s 3p 3d^3$, $3s 3p^3 3d$, $3s 3p^3 4s$, $3s^2 3p 3d^2$, %$3s^2 3p^2 4f$, $3s^2 3p^2 4p$, $3s^2 3p^3$ configurations in Mn~XI (Fe~XII, Co~XIII, Ni~XIV) is provided. The comparison between calculated excitation energies for the $n=4$ states and available experimental values for Fe XII indicate that the calculations are highly accurate, with uncertainties of only a few hundred cm$^{-1}$. Lines from these states are prominent in the soft X-rays. With the present calculations, several recent new identifications are confirmed. Other identifications involving $3p^2 4d$ levels in Fe~XII that were found questionable are discussed and a few new assignments are recommended. As some $n=4$ states of the other ions also show large discrepancies between experimental and calculated energies, we reassess their identification. The present study provides highly accurate atomic data for the $n=4$ states of P-like ions of astrophysical interest, for which experimental data are scarce.

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C. Song, K. Wang, G. Zanna, et. al.
Tue, 3 Mar 20
55/68

Comments: N/A

Search for a Variation of the Fine Structure around the Supermassive Black Hole in Our Galactic Center [GA]

http://arxiv.org/abs/2002.11567


Searching for space-time variations of the constants of Nature is a promising way to search for new physics beyond General Relativity and the standard model motivated by unification theories and models of dark matter and dark energy. We propose a new way to search for a variation of the fine-structure constant using measurements of late-type evolved giant stars from the S-star cluster orbiting the supermassive black hole in our Galactic Center. A measurement of the difference between distinct absorption lines (with different sensitivity to the fine structure constant) from a star leads to a direct estimate of a variation of the fine structure constant between the star’s location and Earth. Using spectroscopic measurements of 5 stars, we obtain a constraint on the relative variation of the fine structure constant below $10^{-5}$. This is the first time a varying constant of Nature is searched for around a black hole and in a high gravitational potential. This analysis shows new ways the monitoring of stars in the Galactic Center can be used to probe fundamental physics.

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A. Hees, T. Do, B. Roberts, et. al.
Thu, 27 Feb 20
12/51

Comments: 7 pages + 10 pages appendix, 3 figures, version accepted for publication

Cavity ring-down spectroscopy of CO$_2$ near $λ$ = 2.06 $μ$m: Accurate transition intensities for the Orbiting Carbon Observatory-2 (OCO-2) "strong band" [CL]

http://arxiv.org/abs/2002.09584


The $\lambda$ = 2.06 $\mu$m absorption band of $^{12}$C$^{16}$O$_2$ is widely used for the remote sensing of atmospheric carbon dioxide, making it relevant to many important top-down measurements of carbon flux. The forward models used in the retrieval algorithms employed in these measurements require increasingly accurate line intensity and line shape data from which absorption cross-sections can be computed. To overcome accuracy limitations of existing line lists, we used frequency-stabilized cavity ring-down spectroscopy to measure 39 transitions in the $^{12}$C$^{16}$O$_2$ absorption band. We estimate the relative combined standard uncertainty for the measured intensities to be $u_r$ = 0.09 %, which is dominated by several type B (systematic) contributions each with $u_r$ = 0.04 %. We predicted the $J$-dependence of the measured intensities using two theoretical models: a one-dimensional quantum mechanical model with Herman-Wallis rotation-vibration corrections, and a line-by-line ab initio model [Zak et al. JQSRT 2016;177:31-42]. For the second approach, we fit only a single factor to rescale the theoretical integrated band intensity to be consistent with the measured intensities. We find that the latter approach yields an equally adequate representation of the fitted $J$-dependent intensity data and provides the most physically general representation of the results. Our recommended value for the integrated band intensity equal to 7.180$\times$10$^{-21}$ cm molecule$^{-1}$ $\pm$ 6$\times$10$^{-24}$ cm molecule$^{-1}$ is based on the rescaled ab initio model and corresponds to a fitted scale factor of 1.0065 $\pm$ 0.0002. Comparisons of literature intensity values to our results reveal systematic deviations ranging from $-$1.1 % to 0.4 %.

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H. Fleurbaey, H. Yi, E. Adkins, et. al.
Tue, 25 Feb 20
66/76

Comments: 30 pages, 9 figures, 4 tables

Extended calculations of energy levels and transition rates for singly ionized lanthanide elements I: Pr – Gd [CL]

http://arxiv.org/abs/2002.08075


Lanthanide elements play important roles as an opacity source in the ejected material from neutron star mergers. Accurate and complete atomic data are necessary to evaluate the opacities and to analyze the observed data. In this paper, we perform extended, ab-initio atomic calculations from Pr II (Z=59) to Gd II (Z=64). By using multiconfiguration Dirac-Hartree-Fock and relativistic configuration-interaction methods, implemented in the general-purpose relativistic atomic structure package GRASP2K, we calculate the energy levels and transition data of electric dipole transitions. These computations are based on strategies (with small variations) of Nd II published by Gaigalas et al. (2019). Accuracy of data is evaluated by comparing computed energy levels with the NIST database or other works. For the energy levels, we obtain the average relative accuracy of 8%, 12%, 6%, 8%, and 7% for Pr II, Pm II, Sm II, Eu II, and Gd II ions, respectively as compared with the NIST data. Accuracy of energy transfer to the wavelength as 3%, 14% and 11% for Pr II, Eu II and Gd II. Our computed E1 type transition probabilities are in good agreement with experimental values presented by other authors especially for strong transitions.

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L. Radžiūtė, G. Gaigalas, D. Kato, et. al.
Thu, 20 Feb 20
41/61

Comments: 20 pages, 14 tables, 11 figures

Calculated line lists for H$_{\text{2}} \mkern0.1mu ^{\text{16}}$O and H$_{\text{2}} \mkern0.1mu ^{\text{18}}$O with extensive comparisons to theoretical and experimental sources including the HITRAN2016 database [EPA]

http://arxiv.org/abs/2002.07658


New line lists are presented for the two most abundant water isotopologues; H${2}$$^{16}$O and H${2}$$^{18}$O. The H${2}$$^{16}$O line list extends to 25710 cm$^{-1}$ with intensity stabilities provided via ratios of calculated intensities obtained from two different semi-empirical potential energy surfaces. The line list for H${2}$$^{18}$O extends to 20000 cm$^{-1}$. The minimum intensity considered for all is $10^{-30}$ cm molecule$^{-1}$ at 296~K, assuming 100\% abundance for each isotopologue. Fluctuation of calculated intensities caused by changes in the underlying potential energy are found to be significant, particularly for weak transitions. Direct comparisons are made against eighteen different sources of line intensities, both experimental and theoretical, many of which are used within the HITRAN2016 database. With some exceptions, there is excellent agreement between our line lists and the experimental intensities in HITRAN2016. In the infrared region, many H${2}$$^{16}$O bands which exhibit intensity differences of 5-10\% between to the most recent ‘POKAZATEL’ line list (Polyansky \textit{et al.}, [Mon. Not. Roy. Astron. Soc. \textbf{480}, 2597 (2018)] and observation, are now generally predicted to within 1\%. For H${2}$$^{18}$O, there are systematic differences in the strongest intensities calculated in this work versus those obtained from semi-empirical calculations. In the visible, computed cross sections show smaller residuals between our work and both HITRAN2016 and HITEMP2010 than POKAZATEL. While our line list accurately reproduces HITEMP2010 cross sections in the observed region, residuals produced from this comparison do however highlight the need to update line positions in the visible spectrum of HITEMP2010. These line lists will be used to update many transition intensities and line positions in the HITRAN2016 database.

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E. Conway, I. Gordon, A. Kyuberis, et. al.
Wed, 19 Feb 20
44/62

Comments: N/A

Energy level structure and transition data of Er$^{2+}$ [CL]

http://arxiv.org/abs/2002.07615


The main aim of this paper is to present accurate energy levels of the ground [Xe]$4f^{12}$ and first excited [Xe]$4f^{11}5d$ configurations of Er$^{2+}$. The energy level structure of the Er$^{2+}$ ion was computed using the multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction (RCI) methods, as implemented in the GRASP2018 program package. The Breit interaction, self-energy and vacuum polarization corrections were included in the RCI computations. The zero-first-order approach was used in the computations. Energy levels with the identification in $LS$ coupling for all (399) states belonging to the [Xe]$4f^{12}$ and [Xe]$4f^{11}5d$ configurations are presented. Electric dipole (E1) transition data between the levels of these two configurations are computed. The accuracy of the these data are evaluated by studying the behaviour of the transition rates as functions of the gauge parameter as well as by evaluating the cancellation factors. The core electron correlations were studied using different strategies. Root-mean-square deviations obtained in this study for states of the ground and excited configurations from the available experimental or semi-empirical data are 649 cm$^{-1}$, and 747 cm$^{-1}$, respectively.

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G. Gaigalas, P. Rynkun, L. Radžiūtė, et. al.
Wed, 19 Feb 20
56/62

Comments: 20 pages, 9 tables, 17 figures

Hydrogen ionization equilibrium in magnetic fields [SSA]

http://arxiv.org/abs/2002.05611


We assess the partition function and ionization degree of magnetized hydrogen atoms at thermodynamic equilibrium for a wide range of field intensities, $B\approx 10^5$-$10^{12}$~G. Evaluations include fitting formulae for an arbitrary number of binding energies, the coupling between the internal atomic structure and the center-of-mass motion across the magnetic field, and the formation of the so-called decentered states (bound states with the electron shifted from the Coulomb well). Non-ideal gas effects are treated within the occupational probability method. We also present general mathematical expressions for the bound state correspondence between the limits of zero-field and high-field. This let us evaluate the atomic partition function in a continuous way from the Zeeman perturbative regime to very strong fields. Results are shown for conditions found in atmospheres of magnetic white dwarf stars (MWDs), with temperatures $T\approx 5000$-$80000$~K and densities $\rho\approx 10^{-12}$-$10^{-3}$~g~cm$^3$. Our evaluations show a marked reduction of the gas ionization due to the magnetic field in the atmospheres of strong MWDs. We also found that decentered states could be present in the atmospheres of currently known hot MWDs, giving a significant contribution to the partition function in the strongest magnetized atmospheres.

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M. Rueda and R. Rohrmann
Fri, 14 Feb 20
1/51

Comments: 15 pages, 10 figures. Accepted for publication in Astronomy & Astrophysics

Expression of the Holtsmark function in terms of hypergeometric $_2F_2$ and Airy $\mathrm{Bi}$ functions [CL]

http://arxiv.org/abs/2001.11893


The Holtsmark distribution has applications in plasma physics, for the electric-microfield distribution involved in spectral line shapes for instance, as well as in astrophysics for the distribution of gravitating bodies. It is one of the few examples of a stable distribution for which a closed-form expression of the probability density function is known. However, the latter is not expressible in terms of elementary functions. In the present work, we mention that the Holtsmark probability density function can be expressed in terms of hypergeometric function $_2F_2$ and of Airy function of the second kind $\mathrm{Bi}$ and its derivative. The new formula is simpler than the one proposed by Lee involving $_2F_3$ and $_3F_4$ hypergeometric functions.

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J. Pain
Mon, 3 Feb 20
17/46

Comments: N/A

Plasma-environment effects on K lines of astrophysical interest III. IPs, K thresholds, radiative rates, and Auger widths in Fe ix – Fe xvi [CL]

http://arxiv.org/abs/2001.11915


Aims. In the context of black-hole accretion disks, we aim to compute the plasma-environment effects on the atomic parameters used to model the decay of K-vacancy states in moderately charged iron ions, namely Fe ix – Fe xvi. Methods. We used the fully relativistic multiconfiguration Dirac-Fock (MCDF) method approximating the plasma electron-nucleus and electron-electron screenings with a time-averaged Debye-Huckel potential. Results. We report modified ionization potentials, K-threshold energies, wavelengths, radiative emission rates, and Auger widths for plasmas characterized by electron temperatures and densities in the ranges $10^5$ – $10^7$ K and $10^{18}$ – $10^{22}$ cm$^{-3}$. Conclusions. This study confirms that the high-resolution X-ray spectrometers onboard the future XRISM and ATHENA space missions will be capable of detecting the lowering of the K edges of these ions due to the extreme plasma conditions occurring in accretion disks around compact objects.

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J. Deprince, M. Bautista, S. Fritzsche, et. al.
Mon, 3 Feb 20
35/46

Comments: 6 pages, 5 figures, to be published in A&A

Diatomic rovibronic transitions as potential probes for proton-to-electron mass ratio across cosmological time [CL]

http://arxiv.org/abs/2001.06121


Astrophysical molecular spectroscopy is an important method of searching for new physics through probing the variation of the proton-to-electron mass ratio, $\mu$, with existing constraints limiting variation to a fractional change of less than 10$^{-17}$/year. To improve on this constraint and therefore provide better guidance to theories of new physics, new molecular probes will be useful. These probes must have spectral transitions that are observable astrophysically and have different sensitivities to variation in the proton-to-electron mass ratio. Here, we concisely detail how astrophysical observations constrain the set of potential molecular probes and promising sensitive transitions based on how the frequency and intensity of these transitions align with available telescopes and observational constraints. Our detailed investigation focuses on rovibronic transitions in astrophysical diatomic molecules, using the spectroscopic models of 11 diatomics to identify sensitive transitions and probe how they generally arise in real complex molecules with many electronic states and fine structure. While none of the 11 diatomics investigated have sensitive transitions likely to be astrophysically observable, we have found that at high temperatures (1000 K) five of these diatomics have a significant number of low intensity sensitive transitions arising from an accidental near-degeneracy between vibrational levels in the ground and excited electronic state. This insight enables screening of all astrophysical diatomics as potential probes of proton-to-electron mass variation, with CN, CP, SiN and SiC being the most promising candidates for further investigation for sensitivity in rovibronic transitions.

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A. Syme, A. Mousley, M. Cunningham, et. al.
Mon, 20 Jan 20
53/60

Comments: N/A

Diatomic rovibronic transitions as potential probes for proton-to-electron mass ratio across cosmological time [CL]

http://arxiv.org/abs/2001.06121


Astrophysical molecular spectroscopy is an important method of searching for new physics through probing the variation of the proton-to-electron mass ratio, $\mu$, with existing constraints limiting variation to a fractional change of less than 10$^{-17}$/year. To improve on this constraint and therefore provide better guidance to theories of new physics, new molecular probes will be useful. These probes must have spectral transitions that are observable astrophysically and have different sensitivities to variation in the proton-to-electron mass ratio. Here, we concisely detail how astrophysical observations constrain the set of potential molecular probes and promising sensitive transitions based on how the frequency and intensity of these transitions align with available telescopes and observational constraints. Our detailed investigation focuses on rovibronic transitions in astrophysical diatomic molecules, using the spectroscopic models of 11 diatomics to identify sensitive transitions and probe how they generally arise in real complex molecules with many electronic states and fine structure. While none of the 11 diatomics investigated have sensitive transitions likely to be astrophysically observable, we have found that at high temperatures (1000 K) five of these diatomics have a significant number of low intensity sensitive transitions arising from an accidental near-degeneracy between vibrational levels in the ground and excited electronic state. This insight enables screening of all astrophysical diatomics as potential probes of proton-to-electron mass variation, with CN, CP, SiN and SiC being the most promising candidates for further investigation for sensitivity in rovibronic transitions.

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A. Syme, A. Mousley, M. Cunningham, et. al.
Mon, 20 Jan 20
43/60

Comments: N/A

Comment on "Energy levels, oscillator strengths, and transition probabilities for sulfur-like scandium, Sc~VI" by El-Maaref et al.\, [Indian J. Phys. {\bf 91} 1029 (2017)] [CL]

http://arxiv.org/abs/2001.05359


In this comment, through our independent calculations, we assess that the recently reported results of El-Maaref et al. [{\em Indian J. Phys.} {\bf 91} 1029 (2017)] for energy levels, oscillator strengths, radiative rates, and lifetimes are inaccurate and unreliable for several levels and transitions of S-like Sc~VI.

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K. Aggarwal
Thu, 16 Jan 20
13/46

Comments: This Comment of 7 pages will appear in the 2020 issue of Indian Journal of Physics

Low-temperature chemistry induced by cosmic rays: positive and negative ions desorption from nitrile-bearing astrophysical ice analogues [SSA]

http://arxiv.org/abs/1912.12368


In cold core of dark molecular clouds, where the UV radiation from external sources is strongly attenuated, cosmic rays can induce chemical reactions on the surface of ice-covered grains promoting the ejection of the processed material to the gas phase. We report the positive and negative secondary ion emission from pure CH3CN, C2H3CN and i-C3H7CN ices due to the bombardment of heavy ions (252Cf fission fragments), simulating the incidence of cosmic rays onto icy surfaces. The secondary ions emitted from each sample were analysed by time-of-flight mass spectrometry (TOF-MS), using Plasma Desorption Mass Spectrometry (PDMS) technique. Several ionic species were identified, indicating strong fragmentation on the frozen surface. Proton-transfer processes are suggested to play a role for positive ion desorption, as evidenced by the protonated RCNH+ parent molecules and (RCN)nH+ ionic clusters. The high electron affinity of the cyano radical seems to contribute to the strong emission of CN-, as well as anions attributed to the CHmCN- fragment and (RCN)nCN- cluster series. Sputtering and desorption of ion clusters (positive and negative) induced by heavy ion bombardment are suggested to constitute a route by which new neutral or ionised molecular species may be delivered to the gas phase where thermal desorption is negligible.

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F. Ribeiro, G. Almeida, W. Wolff, et. al.
Wed, 1 Jan 20
71/88

Comments: N/A

Low-temperature chemistry induced by cosmic rays: positive and negative ions desorption from nitrile-bearing astrophysical ice analogues [SSA]

http://arxiv.org/abs/1912.12368


In cold core of dark molecular clouds, where the UV radiation from external sources is strongly attenuated, cosmic rays can induce chemical reactions on the surface of ice-covered grains promoting the ejection of the processed material to the gas phase. We report the positive and negative secondary ion emission from pure CH3CN, C2H3CN and i-C3H7CN ices due to the bombardment of heavy ions (252Cf fission fragments), simulating the incidence of cosmic rays onto icy surfaces. The secondary ions emitted from each sample were analysed by time-of-flight mass spectrometry (TOF-MS), using Plasma Desorption Mass Spectrometry (PDMS) technique. Several ionic species were identified, indicating strong fragmentation on the frozen surface. Proton-transfer processes are suggested to play a role for positive ion desorption, as evidenced by the protonated RCNH+ parent molecules and (RCN)nH+ ionic clusters. The high electron affinity of the cyano radical seems to contribute to the strong emission of CN-, as well as anions attributed to the CHmCN- fragment and (RCN)nCN- cluster series. Sputtering and desorption of ion clusters (positive and negative) induced by heavy ion bombardment are suggested to constitute a route by which new neutral or ionised molecular species may be delivered to the gas phase where thermal desorption is negligible.

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F. Ribeiro, G. Almeida, W. Wolff, et. al.
Wed, 1 Jan 20
19/88

Comments: N/A

An adaptive gaussian quadrature for the Voigt function [IMA]

http://arxiv.org/abs/1912.08427


We evaluate an adaptive gaussian quadrature integration scheme that will be suitable for the numerical evaluation of generalized redistribution in frequency functions. The latter are indispensable ingredients for “full non-LTE” radiation transfer computations i.e., assuming potential deviations of the velocity distribution of massive particles from the usual Maxwell-Boltzmann distribution. A first validation is made with computations of the usual Voigt profile.

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F. Paletou, C. Peymirat, E. Anterrieu, et. al.
Thu, 19 Dec 19
52/82

Comments: 5 pages, 5 figures

R-matrix electron-impact excitation data for the C-like iso-electronic sequence [SSA]

http://arxiv.org/abs/1912.08466


Emission and absorption features from C-like ions serve as temperature and density diagnostics of astrophysical plasmas. $R$-matrix electron-impact excitation data sets for C-like ions in the literature merely cover a few ions, and often only for the ground configuration. Our goal is to obtain level-resolved effective collision strength over a wide temperature range for C-like ions from \ion{N}{II} to \ion{Kr}{XXXI} (i.e., N$^{+}$ to Kr$^{30+}$) with a systematic set of $R$-matrix calculations. We also aim to assess their accuracy. For each ion, we included a total of 590 fine-structure levels in both the configuration interaction target and close-coupling collision expansion. These levels arise from 24 configurations $2l^3 nl^{\prime}$ with $n=2-4$, $l=0-1$, and $l^{\prime}=0-3$ plus the three configurations $2s^22p5l$ with $l=0-2$. The AUTOSTRUCTURE code was used to calculate the target structure. Additionally, the $R$-matrix intermediate coupling frame transformation method was used to calculate the collision strengths. We compare the present results of selected ions with archival databases and results in the literature. The comparison covers energy levels, transition rates, and effective collision strengths. We illustrate the impact of using the present results on an \ion{Ar}{xiii} density diagnostic for the solar corona. The electron-impact excitation data is archived according to the Atomic Data and Analysis Structure (ADAS) data class adf04 and will be available in OPEN-ADAS. The data will be incorporated into spectral codes, such as CHIANTI and SPEX, for plasma diagnostics.

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J. Mao, N. Badnell and G. Zanna
Thu, 19 Dec 19
77/82

Comments: accepted to A&A

X-ray Spectra from Plasmas with High-Energy Electrons: kappa-distributions and e-e Bremsstrahlung [SSA]

http://arxiv.org/abs/1912.01813


Shocks, turbulence and winds all influence the electron velocity distribution in hot plasmas, exciting lower-energy electrons and generating a high-energy (typically power-law) tail. This effect, typically described as a kappa distribution can affect both the line and continuum X-ray spectrum emitted by the plasma. Hahn & Savin (2015) proposed a “Maxwellian decomposition” to generate the rate coefficients of kappa distributions. Using their method and the AtomDB atomic database, we have developed a general model to calculate the emission from a plasma with a kappa distribution. We compare our kappa results for the charge state distribution and spectra of oxygen to those from KAPPA package with the ion data available within the CHIANTI atomic database. Sufficiently energetic electrons, created either in a kappa distribution or merely a very hot Maxwellian plasma, can also emit via electron-electron (e-e) bremsstrahlung, a process not previously included in AtomDB. We have added this process to AtomDB and apply it to calculate the temperature gradients, as well as the total spectra from the post-shock regions of an accreting magnetic cataclysmic variable (CV). We find the contribution of e-e bremsstrahlung to the total spectra exceeds 10% at KT\sim 100 keV, with the total emissivity in the post-shock accretion stream differing by more than 10% at energies above 60 keV.

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X. Cui, A. Foster, T. Yuasa, et. al.
Thu, 5 Dec 19
52/71

Comments: 10 pages, 7 figures, ApJS in press

New insights on prebiotic chemistry from plasma kinetics [CL]

http://arxiv.org/abs/1912.00647


The famous Miller-Urey experiment, which provides essential information on the prebiotic synthesis of the molecules of life, still has many obscure points. In this paper, we want to suggest a way of possible future progress, which consists in framing the experience of Miller and Urey in the context of the kinetics of ionized gas, or plasma. In this framework, extremely effective and versatile theoretical tools, based on quantum mechanics and chemical kinetics, make it possible to look, in a new way, at the elementary processes that lead to the formation of excited species and ions, at the base of the cascade of subsequent reactions.

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G. Longo, V. Laporta and S. Longo
Tue, 3 Dec 19
71/90

Comments: N/A

Precision frequency-comb terahertz spectroscopy on pure quantum states of a single molecular ion [CL]

http://arxiv.org/abs/1911.12808


Spectroscopy is a powerful tool for studying molecules and is commonly performed on large thermal molecular ensembles that are perturbed by motional shifts and interactions with the environment and one another, resulting in convoluted spectra and limited resolution. Here, we use generally applicable quantum-logic techniques to prepare a trapped molecular ion in a single quantum state, drive terahertz rotational transitions with an optical frequency comb, and read out the final state non-destructively, leaving the molecule ready for further manipulation. We resolve rotational transitions to 11 significant digits and derive the rotational constant of CaH+ to be B_R = 142501777.9(1.7) kHz. Our approach suits a wide range of molecular ions, including polyatomics and species relevant for tests of fundamental physics, chemistry, and astrophysics.

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C. Chou, A. Collopy, C. Kurz, et. al.
Mon, 2 Dec 19
77/91

Comments: 25 pages, 4 figures, 6 tables

AION: An Atom Interferometer Observatory and Network [CEA]

http://arxiv.org/abs/1911.11755


We outline the experimental concept and key scientific capabilities of AION (Atom Interferometer Observatory and Network), a proposed UK-based experimental programme using cold strontium atoms to search for ultra-light dark matter, to explore gravitational waves in the mid-frequency range between the peak sensitivities of the LISA and LIGO/Virgo/ KAGRA/INDIGO/Einstein Telescope/Cosmic Explorer experiments, and to probe other frontiers in fundamental physics. AION would complement other planned searches for dark matter, as well as probe mergers involving intermediate mass black holes and explore early universe cosmology. AION would share many technical features with the MAGIS experimental programme in the US, and synergies would flow from operating AION in a network with this experiment, as well as with other atom interferometer experiments such as MIGA, ZAIGA and ELGAR. Operating AION in a network with other gravitational wave detectors such as LIGO, Virgo and LISA would also offer many synergies.

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L. Badurina, E. Bentine, D. Blas, et. al.
Wed, 27 Nov 19
52/59

Comments: N/A

High-resolution Photo-excitation Measurements Exacerbate the Long-standing Fe XVIII Emission Problem [CL]

http://arxiv.org/abs/1911.09707


We measured the L-shell soft X-ray fluorescence of Fe XVII ions in an electron beam ion trap following resonant photo-excitation using synchrotron radiation provided by the P04 beamline at PETRA III. Special attention is paid to two 2p-3d transitions, the 3C and 3D lines that are essential plasma diagnostics tools for astrophysics. Their resulting oscillator-strength ratio, f(3C)/f(3D) = 3.09(8)(6), is three times more accurate than previous results. The present ratio clearly departs by approximately 5-sigmas from the newest ab initio calculations but confirms previous laboratory measurements and astrophysical observations. A ten thousand-fold reduction in excitation-photon intensity and ten times higher spectral resolution allow us to exclude current explanations, reinstating a forty-year-old atomic-physics puzzle.

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S. Kühn, C. Shah, J. López-Urrutia, et. al.
Mon, 25 Nov 19
4/55

Comments: Main text (6 pages, 3 figures), Supplmentary Material (7 pages, 3 figure), submitted to PRL

Large-scale multiconfiguration Dirac-Hartree-Fock calculations for astrophysics: Cl-like ions from Cr~VIII to Zn~XIV [CL]

http://arxiv.org/abs/1911.03815


We use the multiconfiguration Dirac-Hartree-Fock (MCDHF) method combined with the relativistic configuration interaction (RCI) approach (GRASP2K) to provide a consistent set of transition energies and radiative transition data for the lower $n =3$ states in all Cl-like ions of astrophysical importance, from \ion{Cr}{8} to \ion{Zn}{14}. We also provide excitation energies calculated for \mbox{Fe X} using the many-body perturbation theory (MBPT, implemented within FAC). The comparison of the present MCDHF results with MBPT and with the available experimental energies indicates that the theoretical excitation energies are highly accurate, with uncertainties of only a few hundred cm$^{-1}$. Detailed comparisons for Fe~X and Ni~XII highlight discrepancies in the experimental energies found in the literature. Several new identifications are proposed.

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K. Wang, P. Jönsson, G. Zanna, et. al.
Tue, 12 Nov 19
43/84

Comments: N/A

Constraining symmetron dark energy using atom interferometry [CEA]

http://arxiv.org/abs/1911.00441


Symmetron field is one of the promising candidates of dark energy scalar fields. In all viable candidate field theories, a screening mechanism is implemented to be consistent with existing tests of general relativity. The screening effect in the symmetron theory manifests its influence only to the thin outer layer of a bulk object, where inside a dense material the symmetry of the field is restored and no force exists. For pointlike particles such as atoms, the depth of screening is larger than the size of the particle, such that the screening mechanism is ineffective and the symmetron force is fully expressed on the atomic test particles. Extra force measurements using atom interferometry are thus much more sensitive than bulk mass based measurements, and indeed have placed the most stringent constraints on the parameters characterizing symmetron field in certain region. There is however no clear direct connection between the laboratory measurements and astrophysical observations, where the constraints are far separated by 10 orders of magnitude in the parameter space. In this paper, we present a closed-form expression for the symmetron acceleration of realistic atomic experiments. The expression is validated through numerical simulations for a terrestrial fifth-force experiment using atom interferometry. As a result, we show the connection of the atomic measurement constraints to the astrophysical ones. We also estimate the attainable symmetron constraints from a previously proposed experiment in space intended for test of chameleon theory. The atomic constraints on the symmetron theory will be further improved by orders of magnitude.

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S. Chiow and N. Yu
Mon, 4 Nov 19
19/55

Comments: 10 pages, 7 figures

Effect of the isotropic collisions with neutral hydrogen on the polarization of the CN solar molecule [SSA]

http://arxiv.org/abs/1910.10058


Our work is concerned with the case of the solar molecule CN which presents conspicuous profiles of scattering polarization. We start by calculating accurate PES for the singlet and triplet electronic ground states in order to characterize the collisions between the CN molecule in its $X \; ^2\Sigma$ state and the hydrogen in its ground state $^2S$. The PES are included in the Schr\”oodinger equation to obtain the scattering matrix and the probabilities of collisions. Depolarizing collisional rate coefficients are computed in the framework of the infinite order sudden approximation for temperatures ranging from $T= 2000$ K to $T= 15000$ K. Interpretation of the results and comparison between singlet and triplet collisional rate coefficients are detailed. We show that, for typical photospheric hydrogen density ($n_{H} = 10^{15}-10^{16}$ cm$^{-3}$), the $X \; ^2\Sigma$ state of CN is partially or completely depolarized by isotropic collisions.

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S. Qutub, M. Derouich, Y. Kalugina, et. al.
Wed, 23 Oct 19
62/64

Comments: Accepted for publication in MNRAS (Accepted October 22, 2019). 23 pages, 3 tables, 13 figures

Lifetimes and Oscillator Strengths for Ultraviolet Transitions in Neutral Chlorine [CL]

http://arxiv.org/abs/1910.05803


We present lifetime measurements using beam-foil techniques for radiative transitions from the 3$p^4$($^1S$)4$s$ $^2S_{1/2}$, 3$p^4$($^3P$)5$s$ $^2P_{1/2,3/2}$, and 3$p^4$($^3P$)3$d$ $^2F_{5/2}$ levels in Cl I and the corresponding results of the oscillator strengths for transitions at 1004.68, 1079.88, 1090.73, and 1094.77 \AA, respectively. We compare our experimental results with available theoretical calculations and astronomical observations in an effort to resolve discrepancies among them.

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R. Alkhayat, R. Irving, S. Federman, et. al.
Tue, 15 Oct 19
33/90

Comments: 8 pages, 4 figures

Radiative association of atomic and ionic carbon [CL]

http://arxiv.org/abs/1909.09620


We present calculated cross sections and rate coefficients for the formation of the dicarbon cation (C$_2^+$) by the radiative association process in collisions of a C$(^3P)$ atom and a C$^+(^2P^o)$ ion. Molecular structure calculations for a number of low-lying doublet and quartet states of C$_2^+$ are used to obtain the potential energy surfaces and transition dipole moments coupling the states of interest, substantially increasing the available molecular data for C$_2^+$. Using a quantum-mechanical method, we explore a number of allowed transitions and determine those contributing to the radiative association process. The calculations extend the available data for this process down to the temperature of 100 K, where the rate coefficient is found to be about $2\times 10^{-18}$ cm$^3$/s. We provide analytical fits suitable for incorporation into astrochemical reaction databases.

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J. Babb, R. Smyth and B. McLaughlin
Mon, 23 Sep 19
1/46

Comments: Accepted for publication ApJ

Axion Quark Nuggets and how a Global Network can discover them [CL]

http://arxiv.org/abs/1909.09475


We advocate the idea that a global network of the synchronized axion detectors can greatly enhance the discovery potential of the QCD axions. Our computations are based on the so-called Axion Quark Nugget (AQN) dark matter model which was originally invented to explain the similarity of the dark and visible cosmological matter densities $\Omega_{\rm dark}\sim \Omega_{\rm visible}$. In our framework the conventional population of the galactic axions will be always accompanied by the axions emitted by AQNs. These AQN- originated axions with mass $ 10^{-6} {\rm eV}\lesssim m_a\lesssim 10^{-3}{\rm eV}$ can be observed as correlated events with synchronized detectors assembled in a global network. The correlations can be effectively observed if the individual axion detectors are positioned at distances shorter than a few hundred kilometres.

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D. Budker, V. Flambaum, X. Liang, et. al.
Mon, 23 Sep 19
28/46

Comments: 5 pages. arXiv admin note: text overlap with arXiv:1908.04675, arXiv:1905.00022

Oscillating nuclear electric dipole moments inside atoms [CL]

http://arxiv.org/abs/1909.04970


Interaction with the axion dark matter (DM) field generates an oscillating nuclear electric dipole moment (EDM) with a frequency corresponding to the axion’s Compton frequency. Within an atom, an oscillating EDM can drive electric dipole transitions in the electronic shell. In the absence of radiation, and if the axion frequency matches a dipole transition, it can promote the electron into the excited state. The excitation events can be detected, for example, via subsequent uorescence or photoionization. Here we calculate the rates of such transitions. For a single light atom and an axion Compton frequency resonant with a transition energy corresponding to 1 eV, the rate is on the order of 10^(-22) per year, so a macroscopic atomic sample would be needed. A fundamental challenge is discriminating against background processes that may lead to the excitation of the same electric dipole transition. The ways to enhance the signals to potentially observable levels exceeding backgrounds and to search for axions in an extended frequency range are discussed.

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V. Flambaum, D. Budker and A. Wickenbrock
Thu, 12 Sep 19
34/84

Comments: 4 pages

A prototype industrial laser system for cold atom inertial sensing in space [IMA]

http://arxiv.org/abs/1908.10058


We present the design, realization, characterization and testing of an industrial prototype of a laser system, which is based on frequency doubling of telecom lasers and features all key functionalities to drive a cold atom space gradiometer based on the architecture proposed in [Trimeche et al, 2019]. Testing was performed by implementing the laser system onto a ground based atomic sensor currently under development. The system reaches a Technology Readiness Level (TRL) of 4, corresponding to an operational validation in a controlled environment. The optical architecture of the system can be adapted to other space mission scenarios.

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R. Caldani, S. Merlet, F. Santos, et. al.
Wed, 28 Aug 19
39/60

Comments: N/A

Laboratory Calibrations of Fe XII-XIV Line-Intensity Ratios for Electron Density Diagnostics [SSA]

http://arxiv.org/abs/1908.08094


We have used an electron beam ion trap to measure electron-density-diagnostic line-intensity ratios for extreme ultraviolet lines from F XII, XIII, and XIV at wavelengths of 185-205 255-276 Angstroms. These ratios can be used as density diagnostics for astrophysical spectra and are especially relevant to solar physics. We found that density diagnostics using the Fe XIII 196.53/202.04 and the Fe XIV 264.79/274.21 and 270.52A/274.21 line ratios are reliable using the atomic data calculated with the Flexible Atomic Code. On the other hand, we found a large discrepancy between the FAC theory and experiment for the commonly used Fe XII (186.85 + 186.88)/195.12 line ratio. These FAC theory calculations give similar results to the data tabulated in CHIANTI, which are commonly used to analyze solar observations. Our results suggest that the discrepancies seen between solar coronal density measurements using the Fe XII (186.85 + 186.88)/195.12 and Fe XIII 196.54/202.04 line ratios are likely due to issues with the atomic calculations for Fe XII.

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T. Arthanayaka, P. Beiersdorfer, G. Brown, et. al.
Fri, 23 Aug 19
34/57

Comments: N/A

Near L-edge photoionization of triply charged iron ions [CL]

http://arxiv.org/abs/1908.05252


Relative cross sections for $m$-fold photoionization ($m=1,\ldots,5$) of Fe$^{3+}$ by single photon absorption were measured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source operated at DESY in Hamburg, Germany. The photon energies used spanned the range of $680-950\,\mathrm{eV}$, covering both the photoexcitation resonances from the $2p$ and $2s$ shells as well as the direct ionization from both shells. Multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations were performed to simulate the total photoexcitation spectra. Good agreement was found with the experimental results. These computations helped to assign several strong resonance features to specific transitions. We also carried out Hartree-Fock calculations with relativistic extensions taking into account both photoexcitation and photoionization. Furthermore, we performed extensive MCDHF calculations of the Auger cascades that result when an electron is removed from the $2p$ and $2s$ shells of Fe$^{3+}$. Our theoretically predicted charge-state fractions are in good agreement with the experimental results, representing a substantial improvement over previous theoretical calculations. The main reason for the disagreement with the previous calculations is their lack of inclusion of slow Auger decays of several configurations that can only proceed when accompanied by de-excitation of two electrons. In such cases, this additional shake-down transition of a (sub-)valence electron is required to gain the necessary energy for the release of the Auger electron.

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R. Beerwerth, T. Buhr, A. Perry-Saßmannshausen, et. al.
Thu, 15 Aug 19
23/69

Comments: N/A

Applying matched-filter technique to the search for dark matter transients with networks of quantum sensors [IMA]

http://arxiv.org/abs/1908.03320


There are several networks of precision sensors in existence, including networks of atomic clocks, magnetometers, and gravitational wave detectors. These networks can be re-purposed for searches of exotic physics, such as direct dark matter searches. Here we explore a detection strategy for macroscopic dark matter objects with such networks using the matched-filter technique. Such “clumpy” dark matter objects would register as transients sweeping through the network at galactic velocities. As a specific example, we consider a network of atomic clocks aboard the Global Positioning System (GPS) satellites. We apply the matched-filter technique to simulated GPS atomic clock data and study its utility and performance. The analysis and the developed methodology have a wide applicability to other networks of quantum sensors.

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G. Panelli, B. Roberts and A. Derevianko
Mon, 12 Aug 19
20/42

Comments: 19 pages, 9 figures

AEDGE: Atomic Experiment for Dark Matter and Gravity Exploration in Space [CL]

http://arxiv.org/abs/1908.00802


We propose in this White Paper a concept for a space experiment using cold atoms to search for ultra-light dark matter, and to detect gravitational waves in the frequency range between the most sensitive ranges of LISA and the terrestrial LIGO/Virgo/KAGRA/INDIGO experiments. This interdisciplinary experiment, called Atomic Experiment for Dark Matter and Gravity Exploration (AEDGE), will also complement other planned searches for dark matter, and exploit synergies with other gravitational wave detectors. We give examples of the extended range of sensitivity to ultra-light dark matter offered by AEDGE, and how its gravitational-wave measurements could explore the assembly of super-massive black holes, first-order phase transitions in the early universe and cosmic strings. AEDGE will be based upon technologies now being developed for terrestrial experiments using cold atoms, and will benefit from the space experience obtained with, e.g., LISA and cold atom experiments in microgravity.
Submission in response to the Call for White Papers for the Voyage 2050 long-term plan in the ESA Science Programme. ESA limits White Paper authors to 30. However, we welcome as supporting authors participants in the Workshop on Atomic Experiments for Dark Matter and Gravity Exploration held at CERN: ({\tt https://indico.cern.ch/event/830432/}), as well as any other interested scientists, who can register using this form:{\tt https://indico.cern.ch/event/830432/registrations/52442/}. Registration will close on September 30, 2019, after which a new arXiv version will be prepared and submitted to a journal for publication, listing the supporting authors and taking into account any submitted comments.

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A. Bertoldi, K. Bongs, P. Bouyer, et. al.
Mon, 5 Aug 19
21/53

Comments: N/A

Ab initio Study of Ground-State CS Photodissociation Via Highly Excited Electronic States [GA]

http://arxiv.org/abs/1907.10189


Photodissociation by ultraviolet radiation is the key destruction pathway for CS in photon-dominated regions, such as diffuse clouds. However, the large uncertainties of photodissociation cross sections and rates of CS, resulting from a lack of both laboratory experiments and theoretical calculations, limit the accuracy of calculated abundances of S-bearing molecules by modern astrochemical models. Here we show a detailed \textit{ab initio} study of CS photodissociation. Accurate potential energy curves of CS electronic states were obtained by choosing an active space CAS(8,10) in MRCI+Q/aug-cc-pV(5+d)Z calculation with additional diffuse functions, with a focus on the (B) and (C\,^1\Sigma^+) states. Cross sections for both direct photodissociation and predissociation from the vibronic ground state were calculated by applying the coupled-channel method. We found that the (C-X) ((0-0)) transition has extremely strong absorption due to a large transition dipole moment in the Franck-Condon region and the upper state is resonant with several triplet states via spin-orbit couplings, resulting in predissociation to the main atomic products C ((^3P)) and S ((^1D)). Our new calculations show the photodissociation rate under the standard interstellar radiation field is (2.9\ee{-9})\,s(^{-1}), with a 57\% contribution from (C-X) ((0-0)) transition. This value is larger than that adopted by the Leiden photodissociation and photoionization database by a factor of 3.0. Our accurate \textit{ab initio} calculations will allow more secure determination of S-bearing molecules in astrochemical models.

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Z. Xu, N. Luo, S. Federman, et. al.
Thu, 25 Jul 19
52/72

Comments: 23 pages, 14 figures

SAGE: A Proposal for a Space Atomic Gravity Explorer [IMA]

http://arxiv.org/abs/1907.03867


The proposed mission “Space Atomic Gravity Explorer” (SAGE) has the scientific objective to investigate gravitational waves, dark matter, and other fundamental aspects of gravity as well as the connection between gravitational physics and quantum physics using new quantum sensors, namely, optical atomic clocks and atom interferometers based on ultracold strontium atoms.

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G. Tino, A. Bassi, G. Bianco, et. al.
Wed, 10 Jul 19
16/53

Comments: Submitted to The European Physical Journal D for publication in the Topical Issue “Quantum Technologies for Gravitational Physics”

The effect of hyperfine splitting on Stark broadening for three blue-green Cu I lines in laser-induced plasma [SSA]

http://arxiv.org/abs/1907.02920


Stark effect is observed in many natural and artificial plasmas and is of great importance for diagnostic purposes. Since this effect alters profiles of spectral lines, it should be taken into account when assessing chemical composition of radiation sources, including stars. Copper is one of the elements which studies of stellar atmospheres deal with. To this end, UV and visible Cu lines are used. However, there is a lack of agreement between existing data on their Stark parameters. It is therefore of interest to obtain new experimental data on these lines and to compare them to previous results. In this work, we have estimated Stark widths and shifts for three blue-green lines at 5105.54, 5153.24, and 5218.20 A (corresponding transitions are [3d104p] 2P{\deg} – [3d94s2] 2D and [3d104d] 2D – [3d104p] 2P{\deg}) observed in a “long-spark” laser-induced plasma. For the first time, we have accurately estimated an impact of hyperfine splitting on the profile shapes of the studied lines taking also into account the isotope shifts. We have shown that both effects considerably influence shift and width of Cu I line at 5105.54 A, and shifts of Cu I lines at 5153.24 and 5218.20 A.

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A. Popov, N. Sushkov, S. Zaytsev, et. al.
Mon, 8 Jul 19
7/43

Comments: 16 pages, 7 figures, 6 tables

Search for transient variations of the fine structure constant and dark matter using fiber-linked optical atomic clocks [CEA]

http://arxiv.org/abs/1907.02661


We search for transient variations of the fine structure constant using data from a European network of fiber-linked optical atomic clocks. By searching for coherent variations in the recorded clock frequency comparisons across the network, we significantly improve the constraints on transient variations of the fine structure constant. For example, we constrain the variation in alpha to <5*10^-17 for transients of duration 10^3 s. This analysis also presents a possibility to search for dark matter, the mysterious substance hypothesised to explain galaxy dynamics and other astrophysical phenomena that is thought to dominate the matter density of the universe. At the current sensitivity level, we find no evidence for dark matter in the form of topological defects (or, more generally, any macroscopic objects), and we thus place constraints on certain potential couplings between the dark matter and standard model particles, substantially improving upon the existing constraints, particularly for large (>~10^4 km) objects.

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B. Roberts, P. Delva, A. Al-Masoudi, et. al.
Mon, 8 Jul 19
38/43

Comments: N/A

O($^3P$)+CO$_2$ scattering cross sections at superthermal collision energies for planetary aeronomy [EPA]

http://arxiv.org/abs/1906.11368


We report new elastic and inelastic cross sections for O($^3P$)+CO$_2$ scattering at collision energies from 0.03 to 5 eV, of major importance to O escape from Mars, Venus, and CO$_2$-rich atmospheres. The cross sections were calculated from first principles using three newly constructed ab-initio potential energy surfaces correlating to the lowest energy asymptote of the complex. The surfaces were restricted to a planar geometry with the CO$_2$ molecule assumed to be in linear configuration fixed at equilibrium. Quantum-mechanical coupled-channel formalism with a large basis set was used to compute state-to-state integral and differential cross sections for elastic and inelastic O($^3P$)+CO$_2$ scattering between all pairs of rotational states of CO$_2$ molecule. The elastic cross sections are 35\% lower at 0.5 eV and more than 50\% lower at 4+ eV than values commonly used in studies of processes in upper and middle planetary atmospheres of Mars, Earth, Venus, and CO$_2$-rich planets. Momentum transfer cross sections, of interest for energy transport, were found to be lower than predicted by mass-scaling.

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M. Gacesa, R. Lillis and K. Zahnle
Fri, 28 Jun 19
32/65

Comments: 18 pages, 7 figures; submitted to J. Geophys. Res. Planets

Comment on "Configuration interaction calculations and excitation rates of X-ray and EUV transitions in sulfurlike manganese" by El-Maaref et al. [J. Elect. Spectrosc. Related Phen. 215 (2017) 22] [CL]

http://arxiv.org/abs/1906.08242


In one of the papers, El-Maaref et al. [J. Elect. Spectrosc. Related Phen. 215 (2017) 22] have reported results for energy levels, oscillator strengths (f-values), radiative rates (A-values), collision strengths ($\Omega$), and excitation rates for transitions in S-like Mn~X. However, except for energy levels their results are restricted to only a few transitions and hence have limited application. Furthermore, most of their results have scope for improvement, but for $\Omega$ are not correct as these have been found to be overestimated by an order of magnitude. In this comment we discuss the discrepancies and deficiencies of their results and recommend that a fresh calculation should be performed for this ion.

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K. Aggarwal
Thu, 20 Jun 19
20/51

Comments: 5pp of this paper will soon appear in Journal of Electron Spectroscopy and Related Phenomenon

Mutual neutralization in Li$^+$-D$^-$ collisions: a combined experimental and theoretical study [CL]

http://arxiv.org/abs/1906.06715


We present a combined experimental and theoretical study of the mutual neutralization process in collisions of lithium ions (Li+) with deuterium anions (D-) at collision energies below 1 eV. We employ a merged-beam apparatus to determine total and state-to-state mutual neutralization cross sections. We perform nuclear dynamics calculations using the multi-channel Landau-Zener model based on accurate ab initio molecular data. We obtain an excellent agreement between the experimental and theoretical results over the energy range covered in this work. We show that the basis sets used in the ab initio calculations have a limited influence on the total cross section, but strongly impacts the results obtained for the partial cross sections or the reaction branching ratios. This demonstrates the important role of high-precision measurements to validate the theoretical approaches used to study gas-phase reactive processes. Finally, we compute mutual neutralization rate coefficients for Li+ + H- and Li+ + D-, and discuss their significance for astrochemistry models.

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T. Launoy, J. Loreau, A. Dochain, et. al.
Tue, 18 Jun 19
9/73

Comments: N/A

Energy levels and radiative rates for transitions in S-like Sc~VI, V VIII, Cr IX, and Mn~X [CL]

http://arxiv.org/abs/1906.05860


Energy levels, radiative rates and lifetimes are reported for four S-like ions, namely Sc~VI, V VIII, Cr IX, and Mn~X. Two independent atomic structure codes, namely the general-purpose relativistic atomic structure package ({\sc grasp}) and the flexible atomic code ({\sc fac}), have been adopted for calculating the energy levels, with differing amounts of configuration interaction. This is mainly to make some assessment of accuracy. However, the {\sc grasp} alone is used for calculating the remaining parameters. Results are reported for varying number of levels of these ions, and for calculating lifetimes contributions are included from all types of transitions, i.e. E1, E2, M1, and M2. Comparisons are made with the earlier available experimental and theoretical results and assessments of accuracy are given for each ion. Additionally, the presently reported data cover a significantly larger number of levels and transitions than already available in the literature for the four S-like ions.

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K. Aggarwal
Mon, 17 Jun 19
19/53

Comments: Full paper of about 50pp will soon appear in ADNDT

X-ray spectra of the Fe-L complex [HEAP]

http://arxiv.org/abs/1905.07871


The Hitomi results on the Perseus cluster lead to improvements in our knowledge of atomic physics which are crucial for the precise diagnostic of hot astrophysical plasma observed with high-resolution X-ray spectrometers. However, modeling uncertainties remain, both within but especially beyond Hitomi’s spectral window. A major challenge in spectral modeling is the Fe-L spectrum, which is basically a complex assembly of n>2 to n=2 transitions of Fe ions in different ionization states, affected by a range of atomic processes such as collisional excitation, resonant excitation, radiative recombination, dielectronic recombination, and innershell ionization. In this paper we perform a large-scale theoretical calculation on each of the processes with the flexible atomic code (FAC), focusing on ions of Fe XVII to Fe XXIV that form the main body of the Fe-L complex. The new data are found to be consistent within 20% with the recent individual R-matrix calculations for the main Fe-L lines. By further testing the new FAC calculations with the high-quality RGS data from 15 elliptical galaxies and galaxy clusters, we note that the new model gives systematically better fits than the current SPEX v3.04 code, and the mean Fe abundance decreases by 12%, while the O/Fe ratio increases by 16% compared with the results from the current code. Comparing the FAC fit results to those with the R-matrix calculations, we find a temperature-dependent discrepancy of up to ~10% on the Fe abundance between the two theoretical models. Further dedicated tests with both observed spectra and targeted laboratory measurements are needed to resolve the discrepancies, and ultimately, to get the atomic data ready for the next high-resolution X-ray spectroscopy mission.

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L. Gu, A. Raassen, J. Mao, et. al.
Tue, 21 May 19
43/71

Comments: Accepted for publication in A&A

Dicarbon formation in collisions of two carbon atoms [CEA]

http://arxiv.org/abs/1904.07831


Radiative association cross sections and rates are computed, using a quantum approach, for the formation of C$_2$ molecules (dicarbon) during the collision of two ground state C($^3$P) atoms. We find that transitions originating in the C$\;^1\Pi_g$, d$\;^3\Pi_g$, and 1$\;^5\Pi_u$ states are the main contributors to the process. The results are compared and contrasted with previous results obtained from a semi-classical approximation. New ab initio potential curves and transition dipole moment functions have been obtained for the present work using the multi-reference configuration interaction approach with the Davidson correction (MRCI+Q) and aug-cc-pCV5Z basis sets, substantially increasing the available molecular data on dicarbon. Applications of the current computations to various astrophysical environments and laboratory studies are briefly discussed focusing on these rates.

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J. Babb, R. Smyth and B. McLaughlin
Wed, 17 Apr 19
41/75

Comments: Accepted ApJ

Excitation and charge transfer in low-energy hydrogen atom collisions with neutral carbon and nitrogen [SSA]

http://arxiv.org/abs/1904.00210


Low-energy inelastic collisions with neutral hydrogen atoms are important processes in stellar atmospheres, and a persistent source of uncertainty in non-LTE modelling of stellar spectra. We calculate and study excitation and charge transfer of C i and of N i due to such collisions. We use a previously presented method that is based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions for the adiabatic potential energies, combined with the multichannel Landau-Zener model for the collision dynamics. We find that charge transfer processes typically lead to much larger rate coefficients than excitation processes, consistent with studies of other atomic species. Two-electron processes were considered and lead to non-zero rate coefficients that can potentially impact statistical equilibrium calculations. However, they were included in the model in an approximate way, via an estimate for the two-electron coupling that was presented earlier in the literature: the validity of these data should be checked in a future work.

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A. Amarsi and P. Barklem
Tue, 2 Apr 19
25/90

Comments: 11 pages, 5 figures, 4 tables; accepted for publication in A&A

On the possibility of observable signatures of $ μp $ and $ (μ ^4\mathrm{He})^{+} $ lines on the spectra of astrophysical sources [CL]

http://arxiv.org/abs/1903.11837


We examine the processes of the luminescence in subordinate lines of muonic hydrogen $ \mu p $ and muonic helium ion $ (\mu ^4\mathrm{He})^{+} $ in the presence of background source of X-ray emission. It is supposed that a certain amount of muonic atoms existing in the vicinity of astrophysical source reemits absorbed radiation in the subordinate lines. The intensity of luminescence of such a process is proportional to the quantum yield which was calculated for different pumping channels and different models of spectra. It is shown that the luminescent lines of muonic hydrogen and muonic helium ion can be very noticeable in the spectrum of background source.

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V. Dubrovich and T. Zalialiutdinov
Fri, 29 Mar 19
77/78

Comments: N/A

Revisiting the Fe XVII line emission problem: High-resolution laboratory measurements of the 3s-2p and 3d-2p line-formation channels [HEAP]

http://arxiv.org/abs/1903.04506


We determined relative X-ray photon emission cross sections in Fe XVII ions that were mono-energetically excited in an electron beam ion trap. Line formation for the 3s-2p and 3d-2p transitions of interest proceeds through dielectronic recombination (DR), direct electron-impact excitation (DE), resonant excitation (RE), and radiative cascades. By reducing the electron-energy spread to a sixth of that of previous works and increasing counting statistics by three orders of magnitude, we account for hitherto unresolved contributions from DR and the little-studied RE process to the 3d-2p transitions, and also for cascade population of the 3s-2p line manifold through forbidden states. We found good agreement with state-of-the-art many-body perturbation theory (MBPT) and distorted-wave (DW) method for the 3s-2p transition, while in the 3d-2p transitions known discrepancies were confirmed. Our results show that DW calculations overestimate the 3d-2p line emission due to DE by ~20%. Inclusion of electron-electron correlation effects through the MBPT method in the DE cross section calculations reduces this disagreement by ~11%. The remaining 9% discrepancy is consistent with those found in previous laboratory measurements, solar, and astrophysical observations. Meanwhile, spectral models of opacity, temperature, and turbulence velocity should be adjusted to these experimental cross sections to optimize the accuracy of plasma diagnostics based on these bright soft X-ray lines of Fe XVII.

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C. Shah, J. López-Urrutia, M. Gu, et. al.
Wed, 13 Mar 19
25/125

Comments: 6 pages, 4 figures, submitted to ApJL

CHIANTI – an atomic database for emission lines – Paper XV: Version 9, improvements for the X-ray satellite lines [SSA]

http://arxiv.org/abs/1902.05019


CHIANTI contains a large quantity of atomic data for the analysis of astrophysical spectra. Programs are available in IDL and Python to perform calculation of the expected emergent spectrum from these sources. The database includes atomic energy levels, wavelengths, radiative transition probabilities, rate coefficients for collisional excitation, ionization, and recombination, as well as data to calculate free-free, free-bound, and two-photon continuum emission. In Version 9, we improve the modelling of the satellite lines at X-ray wavelengths by explicitly including autoionization and dielectronic recombination processes in the calculation of level populations for select members of the lithium isoelectronic sequence and Fe XVIII-XXIII. In addition, existing datasets are updated, new ions added and new total recombination rates for several Fe ions are included. All data and IDL programs are freely available at this http URL or through SolarSoft and the Python code ChiantiPy is also freely available at https://github.com/chianti-atomic/ChiantiPy.

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K. Dere, G. Zanna, P. Young, et. al.
Thu, 14 Feb 19
10/52

Comments: Accepted by ApJS, 11 pages, 5 figures

EBIT Observation of Ar Dielectronic Recombination Lines Near the Unknown Faint X-Ray Feature Found in the Stacked Spectrum of Galaxy Clusters [HEAP]

http://arxiv.org/abs/1902.01234


Motivated by possible atomic origins of the unidentified emission line detected at 3.55 keV to 3.57 keV in a stacked spectrum of galaxy clusters (Bulbul et al. 2014), an electron beam ion trap (EBIT) was used to investigate the resonant dielectronic recombination (DR) process in highly-charged argon ions as a possible contributor to the emission feature. The He-like Ar DR-induced transition 1s$^2$2l – 1s2l3l$^\prime$ was suggested to produce a 3.62 keV photon (Bulbul et al. 2014) near the unidentified line at 3.57 keV and was the starting point of our investigation. The collisional-radiative model NOMAD was used to create synthetic spectra for comparison with both our EBIT measurements and with spectra produced with the AtomDB database/Astrophysical Plasma Emission Code (APEC) used in the Bulbul et al. (2014) work. Excellent agreement was found between the NOMAD and EBIT spectra, providing a high level of confidence in the atomic data used. Comparison of the NOMAD and APEC spectra revealed a number of missing features in the AtomDB database near the unidentified line. At an electron temperature of $T_e$ = 1.72 keV, the inclusion of the missing lines in AtomDB increases the total flux in the 3.5 keV to 3.66 keV energy band by a factor of 2. While important, this extra emission is not enough to explain the unidentified line found in the galaxy cluster spectra.

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A. Gall, A. Foster, R. Silwal, et. al.
Tue, 5 Feb 19
55/86

Comments: N/A

Extended calculations of energy levels and transition rates of Nd II-IV ions for application to neutron star mergers [SSA]

http://arxiv.org/abs/1901.10671


Coalescence of binary neutron star give rise to electromagnetic emission, kilonova, powered by radioactive decays of r-process nuclei. Observations of kilonova associated with GW170817 provided unique opportunity to study the heavy element synthesis in the Universe. However, atomic data of r-process elements to decipher the light curves and spectral features of kilonova are not fully constructed yet. In this paper, we perform extended atomic calculations of neodymium (Nd, Z=60) to study the impact of accuracies in atomic calculations to the astrophysical opacities. By employing multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, we calculate energy levels and transition data of electric dipole transitions for Nd II, Nd III, and Nd IV ions. Compared with previous calculations, our new results provide better agreement with the experimental data. The accuracy of energy levels was achieved in the present work 10 %, 3 % and 11 % for Nd II, Nd III and Nd IV, respectively, comparing with the NIST database. We confirm that the overall properties of the opacity are not significantly affected by the accuracies of the atomic calculations. The impact to the Planck mean opacity is up to a factor of 1.5, which affects the timescale of kilonova at most 20 %. However, we find that the wavelength dependent features in the opacity are affected by the accuracies of the calculations. We emphasize that accurate atomic calculations, in particular for low-lying energy levels, are important to provide predictions of kilonova light curves and spectra.

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G. Gaigalas, D. Kato, P. Rynkun, et. al.
Thu, 31 Jan 19
2/59

Comments: 24 pages, 9 figures, The Astrophysical Journal Supplement Series, in press

Uncertainties on atomic data. A case study: N IV [SSA]

http://arxiv.org/abs/1901.08450


We consider three recent large-scale calculations for the radiative and electron-impact excitation data of N IV, carried out with different methods and codes. The scattering calculations employed the relativistic Dirac $R$-matrix (DARC) method, the intermediate coupling frame transformation (ICFT) $R$-matrix method, and the B-spline $R$-matrix (BSR) method. These are all large-scale scattering calculations with well-tested and sophisticated codes, which use the same set of target states. One concern raised in previous literature is related to the increasingly large discrepancies in the effective collision strengths between the three sets of calculations for increasingly weak and/or high-lying transitions. We have built three model ions and calculated the intensities of all the main spectral lines in this ion. We have found that, despite such large differences, excellent agreement (to within $\pm$~20\%) exists between all the spectroscopically-relevant line intensities. This provides confidence in the reliability of the calculations for plasma diagnostics. We have used the differences in the radiative and excitation rates amongst the three sets of calculations to obtain a measure of the uncertainty in each rate. Using a Monte Carlo approach, we have shown how these uncertainties affect the main theoretical ratios which are used to measure electron densities and temperatures.

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G. Zanna, L. Fernandez-Menchero and N. Badnell
Fri, 25 Jan 19
46/58

Comments: Accepted for publication

Atomic source selection in space-borne gravitational wave detection [CL]

http://arxiv.org/abs/1812.11348


Recent proposals for space-borne gravitational wave detectors based on atom interferometry rely on extremely narrow single-photon transition lines as featured by alkaline-earth metals or atomic species with similar electronic configuration. Despite their similarity, these species differ in key parameters such as abundance of isotopes, atomic flux, density and temperature regimes, achievable expansion rates, density limitations set by interactions, as well as technological and operational requirements. In this study, we compare viable candidates for gravitational wave detection with atom interferometry, contrast the most promising atomic species, identify the relevant technological milestones and investigate potential source concepts towards a future gravitational wave detector in space.

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S. Loriani, D. Schlippert, C. Schubert, et. al.
Tue, 1 Jan 19
4/55

Comments: N/A

Atomic source selection in space-borne gravitational wave detection [CL]

http://arxiv.org/abs/1812.11348


Recent proposals for space-borne gravitational wave detectors based on atom interferometry rely on extremely narrow single-photon transition lines as featured by alkaline-earth metals or atomic species with similar electronic configuration. Despite their similarity, these species differ in key parameters such as abundance of isotopes, atomic flux, density and temperature regimes, achievable expansion rates, density limitations set by interactions, as well as technological and operational requirements. In this study, we compare viable candidates for gravitational wave detection with atom interferometry, contrast the most promising atomic species, identify the relevant technological milestones and investigate potential source concepts towards a future gravitational wave detector in space.

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S. Loriani, D. Schlippert, C. Schubert, et. al.
Tue, 1 Jan 19
36/55

Comments: N/A

Experiment to detect dark energy forces using atom interferometry [CL]

http://arxiv.org/abs/1812.08244


The accelerated expansion of the universe motivates a wide class of scalar field theories that modify gravity on large scales. In regions where the weak field limit of General Relativity has been confirmed by experiment, such theories need a screening mechanism to suppress the new force. We have measured the acceleration of an atom toward a macroscopic test mass inside a high vacuum chamber, where the new force is unscreened in some theories. Our measurement, made using atom interferometry, shows that the attraction between atoms and the test mass does not differ appreciably from Newtonian gravity. This result places stringent limits on the free parameters in chameleon and symmetron theories of modified gravity.

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D. Sabulsky, I. Dutta, E. Hinds, et. al.
Fri, 21 Dec 18
38/72

Comments: 6 pages, 4 figures

MAGIS-100 at Fermilab [CL]

http://arxiv.org/abs/1812.00482


MAGIS-100 is a next-generation instrument that uses light-pulse atom interferometry to search for physics beyond the standard model, to be built and installed at Fermilab. We propose to search for dark matter and new forces, and to test quantum mechanics at new distance scales. The detector will use the existing 100 m vertical NuMI access shaft to make it the world’s longest baseline atom interferometer. To maximize the sensitivity of the experiment, we will use the latest advances in atomic clock technologies. The experiment will be a significant step towards developing a 1000 m baseline detector, with sufficient sensitivity to detect gravitational waves in the `mid-band’ from 0.1 Hz – 10 Hz, between the Advanced LIGO and LISA experiments. Here we describe an overview of the experiment and its physics reach.

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J. Coleman
Tue, 4 Dec 18
32/78

Comments: Prepared for the proceedings of ICHEP 2018, International Conference on High Energy Physics, 4-11 July 2018

Perspectives on Astrophysics Based on Atomic, Molecular, and Optical (AMO) Techniques [CL]

http://arxiv.org/abs/1811.06157


About two generations ago, a large part of AMO science was dominated by experimental high energy collision studies and perturbative theoretical methods. Since then, AMO science has undergone a transition and is now dominated by quantum, ultracold, and ultrafast studies. But in the process, the field has passed over the complexity that lies between these two extremes. Most of the Universe resides in this intermediate region. We put forward that the next frontier for AMO science is to explore the AMO complexity that describes most of the Cosmos.

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D. Savin, J. Babb, P. Bellan, et. al.
Fri, 16 Nov 18
2/78

Comments: White paper submission to the Decadal Assessment and Outlook Report on Atomic, Molecular, and Optical (AMO) Science (AMO 2020)

Oscillator Strengths for Ultraviolet Transitions in P II -The Multiplet at 1308 Å [CL]

http://arxiv.org/abs/1810.04533


We report lifetimes, branching fractions, and the resulting oscillator strengths for transitions within the P II multiplet (3s23p2 3P – 3s3p3 3Po) at 1308 {\AA}. These comprehensive beam-foil measurements, which are the most precise set currently available experimentally, resolve discrepancies involving earlier experimental and theoretical results. Interstellar phosphorus abundances derived from {\lambda}1308 can now be interpreted with greater confidence. In the course of our measurements, we also obtained an experimental lifetime for the 3p4s 3P0o level of P IV. This lifetime agrees well with the available theoretical calculation.

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M. Brown, R. Alkhayat, R. Irving, et. al.
Thu, 11 Oct 18
38/72

Comments: 10 pages, 3 figures

Spectroscopy of low-ionized iron-peak elements. Electron-impact excitation of Ni$^{3+}$ and photoionisation of Ni$^{2+}$ [IMA]

http://arxiv.org/abs/1809.05472


The spectra from Fe-peak elements may be used to determine the temperature and density of various astrophysical objects. Determination of these quantities is underpinned by the accuracy and the comprehensiveness of the underlying atomic structure and collisional calculations. In the following paper, we shall focus specifically on Ni IV lines associated with transitions amongst several low-lying levels. We shall employ modified versions of the parallel Dirac R-matrix codes, considering both electron-impact excitation of Ni$^{3+}$ and the photoionisation of both the ground and excited states of Ni$^{2+}$. We produce high-quality data sets for both processes, and using these data, we calculate line ratios relevant for plasma diagnostics of temperature and density.

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L. Fernández-Menchero, R. Smyth, C. Ramsbottom, et. al.
Mon, 17 Sep 18
1/45

Comments: 12 pages, 7 figures, 5 tables

Anomalous phosphine sensitivity coefficients as probes for a possible variation of the proton-to-electron mass ratio [CEA]

http://arxiv.org/abs/1808.05427


A robust variational approach is used to investigate the sensitivity of the rotation-vibration spectrum of phosphine (PH$3$) to a possible cosmological variation of the proton-to-electron mass ratio, $\mu$. Whilst the majority of computed sensitivity coefficients, $T$, involving the low-lying vibrational states acquire the expected values of $T\approx-1$ and $T\approx-1/2$ for rotational and ro-vibrational transitions, respectively, anomalous sensitivities are uncovered for the $A_1!-!A_2$ splittings in the $\nu_2/\nu_4$, $\nu_1/\nu_3$ and $2\nu_4^{\ell=0}/2\nu_4^{\ell=2}$ manifolds of PH$_3$. A pronounced Coriolis interaction between these states in conjunction with accidentally degenerate $A_1$ and $A_2$ energy levels produces a series of enhanced sensitivity coefficients. Phosphine is expected to occur in a number of different astrophysical environments and has potential for investigating a drifting constant. Furthermore, the displayed behaviour hints at a wider trend in molecules of ${\bf C}{3\mathrm{v}}\mathrm{(M)}$ symmetry, thus demonstrating that the splittings induced by higher-order ro-vibrational interactions are well suited for probing $\mu$ in other symmetric top molecules in space, since these low-frequency transitions can be straightforwardly detected by radio telescopes.

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A. Owens, S. Yurchenko and V. Špirko
Fri, 17 Aug 18
26/53

Comments: N/A

Precision spectroscopy and comprehensive analysis of perturbations in the $A\,{}^1Π(v=0$) state of ${}^{\rm 13}$C${}^{\rm 18}$O [CL]

http://arxiv.org/abs/1808.02476


We have reinvestigated the A$^1\Pi$$(v=0)$ level of $^{13}$C$^{18}$O\ using new high-resolution spectra obtained via multi-photon laser excitation as well as with synchrotron-based Fourier-transform absorption spectroscopy of the A$^1\Pi -\textrm{X}^1\Sigma^+$$(0, 0)$, e$^3\Sigma^–\textrm{X}^1\Sigma^+$$(1, 0)$, d$^3\Delta-\textrm{X}^1\Sigma^+$$(4, 0)$, a$’^3\Sigma^+-\textrm{X}^1\Sigma^+$$(9, 0)$, and \atX$(11, 0)$ bands. In addition, Fourier-transform emission spectroscopy in the visible range is performed on the ${\rm B}^1\Sigma^+-{\rm A}^1\Pi$$(0, 0)$ band. Spectra of the \BX$(0, 0)$ band are measured in order to tie information from the latter emission data to the level structure of A$^1\Pi$$(v=0)$. The high pressures in the absorption cell at the synchrotron and the high temperatures in the emission discharge permitted monitoring of high rotational quantum levels in A$^1\Pi$$(v=0)$ up to $J=43$. All information, in total over 900 spectral lines, was included in an effective-Hamiltonian analysis of the A$^1\Pi(v=0, J)$ levels that are directly perturbed by the e$\,^3\Sigma^-$$(v=1)$, d$^3!\Delta$$(v=4)$, a$’^3\Sigma^+$$(v=9)$, d$^3!\Delta$$(v=0)$, I$\,^1\Sigma^-$$(v=0, 1)$ close-lying levels and the e$\,^3\Sigma^-$$(v=0,2)$, d$^3!\Delta$$(v=3,5)$, a$’^3\Sigma^+$$(v=8,10)$ remote levels, as well being indirectly influenced by the a$^3\Pi$$(v=10, 11)$ state. The influence of nine further perturber levels and their interactions was investigated and are not significant for reproducing the present experimental data. This analysis leads to a much improved description in terms of molecular constants and interaction parameters, compared to previous studies of the same energy region for other CO isotopologues.

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R. Hakalla, T. Trivikram, A. Heays, et. al.
Wed, 8 Aug 18
22/54

Comments: accepted Molecular Physics

Measuring masses in low mass X-ray binaries via X-ray spectroscopy: the case of MXB 1659-298 [HEAP]

http://arxiv.org/abs/1807.04757


The determination of fundamental parameters in low-mass X-ray binaries typically relies on measuring the radial velocity curve of the companion star through optical or near-infrared spectroscopy. It was recently suggested that high resolution X-ray spectroscopy might enable a measurement of the radial velocity curve of the compact object by monitoring the Doppler shifts induced by the orbital motion of the disc wind or the disc atmosphere. We analysed a Chandra-HETG+NuSTAR soft state observation of MXB 1659-298, an eclipsing neutron star low-mass X-ray binary (LMXB). We measured a radial velocity curve whose phase offset and semi-amplitude are consistent with the primary star. We derived the value for the semi-amplitude of the radial velocity for the compact object $K_1=89\pm19$ km s$^{-1}$, constrained the mass of the secondary ($0.3\leq M_2\leq0.8$ M$_\odot$) and the orbital inclination of the binary system ($73\leq i\leq77^\circ$). These values are consistent with previous estimates from independent methods. Via the same technique, the next generation of X-ray observatories equipped with high spectral resolution instruments (e.g., Athena) will have the potential to measure the radial velocity curve of the primary in high inclination X-ray binaries to an accuracy of a few per cent.

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G. Ponti, S. Bianchi, T. Muñoz-Darias, et. al.
Mon, 16 Jul 18
38/55

Comments: Accepted for publication in MNRAS Letters

Resonance strengths for KLL dielectronic recombination of highly charged mercury ions and improved empirical $\boldsymbol{Z}$-scaling law [CL]

http://arxiv.org/abs/1807.03366


Theoretical and experimental resonance strengths for KLL dielectronic recombination (DR) into He-, Li-, Be-, and B-like mercury ions are presented, based on state-resolved DR x-ray spectra recorded at the Heidelberg electron beam ion trap. The DR resonance strengths were experimentally extracted by normalizing them to simultaneously recorded radiative recombination signals. The results are compared to state-of-the-art atomic calculations that include relativistic electron-electron correlation and configuration mixing effects. Combining the present data with other existing ones, we derive an improved semi-empirical $Z$-scaling law for DR resonance strength as a function of the atomic number, taking into account higher-order relativistic corrections, which are especially relevant for heavy highly charged ions.

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Z. Harman, C. Shah, A. González-Martínez, et. al.
Wed, 11 Jul 18
9/64

Comments: 11 pages, 4 figures, submitted to Phys. Rev. A

K-shell photoabsorption and photoionization of trace elements. III. Isoelectronic sequences with electron number $19\leq N\leq 26$ [CL]

http://arxiv.org/abs/1807.02112


This is the final report of a three-paper series on the K-shell photoabsorption and photoionization of trace elements, namely F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu and Zn. K lines and edges from such elements are observed in the X-ray spectra of supernova remnants, galaxy clusters and accreting black holes and neutron stars, their diagnostic potential being limited by poor atomic data. We are completing the previously reported radiative datasets with new photoabsorption and photoionization cross sections for isoelectronic sequences with electron number $19\leq N\leq 26$. We are also giving attention to the access, integrity and usability of the whole resulting atomic database. Target representations are obtained with the atomic structure code AUTOSTRUCTURE. Where possible, cross sections for ground-configuration states are computed with the Breit–Pauli $R$-matrix method (BPRM) in either intermediate or $LS$ coupling including damping (radiative and Auger) effects; otherwise and more generally, they are generated in the isolated-resonance approximation with AUTOSTRUCTURE. Cross sections were computed with BPRM only for the K ($N=19$) and Ca ($N=20$) isoelectronic sequences, the latter in $LS$ coupling. For the rest of the sequences ($21\leq N \leq 26$), AUTOSTRUCTURE was run in $LS$-coupling mode taking into account damping effects. Comparisons between these two methods for K-like Zn XII and Ca-like Zn XI show that, to ensure reasonable accuracy, the $LS$ calculations must be performed taking into account the non-fine-structure relativistic corrections.

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C. Mendoza, M. Bautista, P. Palmeri, et. al.
Mon, 9 Jul 18
27/43

Comments: 7 pages, 3 figures. Accepted for publication in Astronomy & Astrophysics

First observation with global network of optical atomic clocks aimed for a dark matter detection [CL]

http://arxiv.org/abs/1806.04762


We report on the first earth-scale quantum sensor network based on optical atomic clocks aimed at dark matter (DM) detection. Exploiting differences in the susceptibilities to the fine-structure constant of essential parts of an optical atomic clock, i.e. the cold atoms and the optical reference cavity, we can perform sensitive searches for dark matter signatures without the need of real-time comparisons of the clocks. We report a two orders of magnitude improvement in constraints on transient variations of the fine-structure constant, which considerably improves the detection limit for the standard model (SM) – DM coupling. We use Yb and Sr optical atomic clocks at four laboratories on three continents to search for both topological defect (TD) and massive scalar field candidates. No signal consistent with a dark-matter coupling is identified, leading to significantly improved constraints on the DM-SM couplings.

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P. Wcisło, P. Ablewski, K. Beloy, et. al.
Thu, 14 Jun 18
6/49

Comments: N/A

Theoretical study of ArH+ dissociative recombination and electron-impact vibrational excitation [GA]

http://arxiv.org/abs/1806.03966


Cross sections are presented for dissociative recombination and electron-impact vibrational excitation of the ArH+ molecular ion at electron energies appropriate for the interstellar environment. The R-matrix method is employed to determine the molecular structure data, i.e. the position and width of the resonance states. The cross sections and the corresponding Maxwellian rate coefficients are computed using a method based on the Multichannel Quantum Defect Theory. The main result of the paper is the very low dissociative recombination rate found at temperatures below 1000K. This is in agreement with the previous upper limit measurement in merged beams and offers a realistic explanation to the presence of ArH+ in exotic interstellar conditions.

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A. Abdoulanziz, F. Colboc, D. Little, et. al.
Tue, 12 Jun 18
71/79

Comments: 6 pages; 7 figures

Local burst model of CMB temperature fluctuations: luminescence in lines of primary para- and orthohelium [CL]

http://arxiv.org/abs/1806.00542


The formation of the luminescent subordinate HeI lines by the absorption of radiation from a source in lines of main HeI series in the expanding Universe is considered. It is suggested that at some instant of time, corresponding to the redshift $z_{0}$, a burst of radiation occurs in the continuum. This radiation is partially absorbed at different $z <z_{0}$ in the lines of the main HeI series (different pumping channels) and then partially converted into radiation in subordinate lines. If $ \nu_{ij} $ is the laboratory frequency of the transition of some subordinate line originating at some $z$, then in the present time its frequency will be $ \nu=\nu_{ij}/(1+z) $. For different $z$ (and, consequently, for different $ \nu $), the radiation escape for the subordinate lines of para- and orthohelium is calculated, i.e. the number of photons emitted in the subordinate line, per one initial excited atom. Different pumping channels are considered. It is shown that the same luminescent lines can be both emission and absorption ones, depending on the initial excitation. The importance of accounting for forbidden transitions is discussed.

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V. Dubrovich and T. Zalialiutdinov
Tue, 5 Jun 18
14/68

Comments: N/A

X-ray ionization of the intergalactic medium by quasars [CEA]

http://arxiv.org/abs/1805.11615


We investigate the impact of quasars on the ionization of the surrounding intergalactic medium (IGM) with the radiative transfer code \texttt{CRASH4}, now accounting for X-rays and secondary electrons. After comparing with analytic solutions, we post-process a cosmic volume ($ \approx 1.5\times 10^4$ Mpc$^3 h^{-3}$) containing a ULAS J1120+0641-like quasar (QSO) hosted by a $5 \times 10^{11} {\rm M}\odot h^{-1}$ dark matter (DM) halo. We find that: (i) the average HII region ($R\sim3.2$~pMpc in a lifetime $t_f = 10^7$~yrs) is mainly set by UV flux, in agreement with semi-analytic scaling relations; (ii) a largely neutral ($x{\textrm{HII}} < 0.001$), warm ($T\sim 10^3$~K) tail extends up to few Mpc beyond the ionization front, as a result of the X-ray flux; (iii) LyC-opaque inhomogeneities induce a line of sight (LOS) scatter in $R$ as high as few physical Mpc, consistent with the DLA scenario proposed to explain the anomalous size of the ULAS J1120+0641 ionized region. On the other hand, with an ionization rate $\dot{N}_{\gamma,0} \sim 10^{57}$~s$^{-1}$, the assumed DLA clustering and gas opacity, only one LOS shows an HII region compatible with the observed one. We deduce that either the ionization rate of the QSO is at least one order of magnitude lower or the ULAS J1120+0641 bright phase is shorter than $10^7$~yrs.

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L. Graziani, B. Ciardi and M. Glatzle
Wed, 30 May 18
56/65

Comments: Accepted for publication in MNRAS Main Journal, Accepted 2018 May 21

Analysis of the absorption line profile at 21 cm for the hydrogen atom in interstellar medium [CL]

http://arxiv.org/abs/1805.01211


In this paper an analysis of the absorption line profile at $21$ cm hyperfine transition of hydrogen atom in interstellar medium is carried out. It is shown that in most cases the dominant contribution to the profile formation occurs with the account for the additional field on adjacent resonance for the hydrogen atom at rest. The field acting on neighboring resonances leads to the physical processes which can be explained as the interfering pathways between different transitions. In this case the correction to the optical depth can be introduced. A significant none-Doppler broadening of the line profile is found, the frequency shift is determined also. It is shown that the additional physical processes in atom should be taken into account for the detailed analysis of the absorption line profile and for the accurate determination of optical depth and column densities in hydrogen interstellar medium.

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D. Solovyev
Fri, 4 May 18
61/65

Comments: 12 pages

Radiative Charge Transfer Between the Helium Ion and Argon [GA]

http://arxiv.org/abs/1804.10108


The rate coefficient for radiative charge transfer between the helium ion and an argon atom is calculated. The rate coefficient is about $10^{-14}$ cm${}^3$/s at 300 K in agreement with earlier experimental data.

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J. Babb and B. McLaughlin
Fri, 27 Apr 18
-51/64

Comments: N/A

A Quantitative Comparison of Opacities Calculated Using the Distorted- Wave and $\boldsymbol{R}$-Matrix Methods [SSA]

http://arxiv.org/abs/1804.03365


The present debate on the reliability of astrophysical opacities has reached a new climax with the recent measurements of Fe opacities on the Z-machine at the Sandia National Laboratory \citep{Bailey2015}. To understand the differences between theoretical results, on the one hand, and experiments on the other, as well as the differences among the various theoretical results, detailed comparisons are needed. Many ingredients are involved in the calculation of opacities; deconstructing the whole process and comparing the differences at each step are necessary to quantify their importance and impact on the final results. We present here such a comparison using the two main approaches to calculate the required atomic data, the $R$-Matrix and distorted-wave methods, as well as sets of configurations and coupling schemes to quantify the effects on the opacities for the $Fe\ XVII$ and $Ni\ XIV$ ions.

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F. Delahaye, N. Badnell, C. Ballance, et. al.
Wed, 11 Apr 18
17/54

Comments: 10 pages, 2 figures

Photodissociation of CS from Excited Rovibrational Levels [CL]

http://arxiv.org/abs/1804.01091


Accurate photodissociation cross sections have been computed for transitions from the X {$^1\Sigma^+$} ground electronic state of CS to six low-lying excited electronic states. New ab initio potential curves and transition dipole moment functions have been obtained for these computations using the multi-reference configuration interaction approach with the Davidson correction (MRCI+Q) and aug-cc-pV6Z basis sets. State-resolved cross sections have been computed for transitions from nearly the full range of rovibrational levels of the X {$^1\Sigma^+$} state and for photon wavelengths ranging from 500 {\AA} to threshold. Destruction of CS via predissociation in highly-excited electronic states originating from the rovibrational ground state is found to be unimportant. Photodissociation cross sections are presented for temperatures in the range between 1,000 K to 10,000 K, where a Boltzmann distribution of initial rovibrational levels is assumed. Applications of the current computations to various astrophysical environments are briefly discussed focusing on photodissociation rates due to the standard interstellar and black-body radiation fields.

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R. Pattillo, R. Cieszewski, P. Stancil, et. al.
Thu, 5 Apr 18
36/50

Comments: 16 pages, 9 figures

Search for transient ultralight dark matter signatures with networks of precision measurement devices using a Bayesian statistics method [IMA]

http://arxiv.org/abs/1803.10264


We analyze the prospects of employing a distributed global network of precision measurement devices as a dark matter and exotic physics observatory. In particular, we consider the atomic clocks of the Global Positioning System (GPS), consisting of a constellation of 32 medium-Earth orbit satellites equipped with either Cs or Rb microwave clocks and a number of Earth-based receiver stations, some of which employ highly-stable H-maser atomic clocks. High-accuracy timing data is available for almost two decades. By analyzing the satellite and terrestrial atomic clock data, it is possible to search for transient signatures of exotic physics, such as “clumpy” dark matter and dark energy, effectively transforming the GPS constellation into a 50,000km aperture sensor array. Here we characterize the noise of the GPS satellite atomic clocks, describe the search method based on Bayesian statistics, and test the method using simulated clock data. We present the projected discovery reach using our method, and demonstrate that it can surpass the existing constrains by several order of magnitude for certain models. Our method is not limited in scope to GPS or atomic clock networks, and can also be applied to other networks of precision measurement devices.

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B. Roberts, G. Blewitt, C. Dailey, et. al.
Thu, 29 Mar 18
3/63

Comments: See also Supplementary Information located in ancillary files

Interference-assisted resonant detection of axions [CL]

http://arxiv.org/abs/1803.09388


Detection schemes for the quantum chromodynamics axions and other axion-like particles in light-shining-through-a-wall (LSW) experiments are based on the conversion of these particles into photons in a magnetic field. An alternative scheme may involve the detection via a resonant atomic or molecular transition induced by resonant axion absorption. The signal obtained in this process is second order in the axion-electron interaction constant but may become first order if we allow interference between the axion-induced transition amplitude and the transition amplitude induced by the electromagnetic radiation that produces the axions.

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H. Tan, V. Flambaum, I. Samsonov, et. al.
Wed, 28 Mar 18
52/148

Comments: 12 pages, 4 figures, 3 tables

Inside a VAMDC data node – Putting standards into practical software [IMA]

http://arxiv.org/abs/1803.09217


Access to molecular and atomic data is critical for many forms of remote sensing analysis across different fields. Many atomic and molecular databases are however highly specialized for their intended application, complicating querying and combination data between sources. The Virtual Atomic and Molecular Data Centre, VAMDC, is an electronic infrastructure that allows each database to register as a “node”. Through services such as VAMDC’s portal website, users can then access and query all nodes in a homogenized way. Today all major Atomic and Molecular databases are attached to VAMDC.
This article describes the software tools we developed to help data providers create and manage a VAMDC node. It gives an overview of the VAMDC infrastructure and of the various standards it uses. The article then discusses the development choices made and how the standards are implemented in practice. It concludes with a full example of implementing a VAMDC node using a real-life case as well as future plans for the node software.

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S. Regandell, T. Marquart and N. Piskunov
Wed, 28 Mar 18
142/148

Comments: 12 pages, 2 figures

High magnetic fields for fundamental physics [CL]

http://arxiv.org/abs/1803.07547


Various fundamental-physics experiments such as measurement of the birefringence of the vacuum, searches for ultralight dark matter (e.g., axions), and precision spectroscopy of complex systems (including exotic atoms containing antimatter constituents) are enabled by high-field magnets. We give an overview of current and future experiments and discuss the state-of-the-art DC- and pulsed-magnet technologies and prospects for future developments.

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R. Battesti, J. Beard, S. Boser, et. al.
Wed, 21 Mar 2018
19/61

Comments: 49 pages, 32 figures

Precision measurement noise asymmetry and its annual modulation as a dark matter signature [CL]

http://arxiv.org/abs/1803.00617


Dark matter may be composed of ultralight quantum fields that form macroscopic objects. As the Earth moves through the galaxy, interactions with such objects may leave transient signatures in terrestrial experiments. These signatures may be sought by analyzing correlations between multiple devices in a distributed network. However, if the objects are small (<~10^3 km) it becomes unlikely that more than one device will be affected in a given event. Such models may, however, induce an observable asymmetry in the noise distributions of precision measurement devices, such as atomic clocks. Further, an annual modulation in this asymmetry is expected. Such an analysis may be performed very simply using existing data, and would be sensitive to models with a high event rate, even if individual events cannot be resolved. For certain models, our technique extends the discovery reach beyond that of existing experiments by many orders of magnitude.

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B. Roberts and A. Derevianko
Mon, 5 Mar 18
31/45

Comments: N/A

Detecting dark matter waves with precision measurement tools [CL]

http://arxiv.org/abs/1605.09717


Virialized Ultra-Light Fields (VULFs) are viable cold dark matter candidates and include scalar and pseudo-scalar bosonic fields, such as axions and dilatons. Direct searches for VULFs rely on low-energy precision measurement tools. While the previous proposals have focused on detecting coherent oscillations of the VULF signals at the VULF Compton frequencies at individual devices, here I consider a network of such devices. VULFs are essentially dark matter {\em waves} and as such they carry both temporal and spatial phase information. Thereby, the discovery reach can be improved by using networks of precision measurement tools. To formalize this idea, I derive a spatio-temporal two-point correlation function for the ultralight dark matter fields in the framework of the standard halo model. Due to VULFs being Gaussian random fields, the derived two-point correlation function fully determines $N$-point correlation functions. For a network of $N_{d}$ devices within the coherence length of the field, the sensitivity compared to a single device can be improved by a factor of $\sqrt{N_{d}}$. Further, I derive a VULF dark matter signal profile for an individual device. The resulting line shape is strongly asymmetric due to the parabolic dispersion relation for massive non-relativistic bosons. I discuss the aliasing effect that extends the discovery reach to VULF frequencies higher than the experimental sampling rate. I present sensitivity estimates and develop a stochastic field SNR statistic. Finally, I consider an application of the developed formalism to atomic clocks and their networks.

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A. Derevianko
Thu, 22 Feb 18
30/60

Comments: 16 pages, 5 figs. Revised and expanded version

Constraining screened fifth forces with the electron magnetic moment [CL]

http://arxiv.org/abs/1802.05545


Chameleon and symmetron theories serve as archetypal models for how light scalar fields can couple to matter with gravitational strength or greater, yet evade the stringent constraints from classical tests of gravity on Earth and in the Solar System. In this work, we investigate how a precision measurement of the electron magnetic moment places meaningful constraints on both chameleons and symmetrons. Two effects are identified: First, virtual chameleons and symmetrons run in loops to generate quantum corrections to the intrinsic value of the magnetic moment; a common process widely considered in the literature for many beyond-the-Standard-Model scenarios. A second effect, however, is unique to scalar fields that exhibit screening. A scalar bubble-like profile forms inside the experimental vacuum chamber and exerts a fifth force on the electron, leading to a systematic shift in the experimental measurement. In quantifying this latter effect, we present a novel approach that combines analytic arguments and a small number of numerical simulations to solve for the bubble-like profile quickly for a large range of model parameters. Taken together, both effects yield interesting constraints in complementary regions of parameter space. While the constraints we obtain for the chameleon are largely uncompetitive with those in the existing literature, this still represents the tightest constraint achievable yet from an experiment not originally designed to search for fifth forces. We break more ground with the symmetron, for which our results exclude a large and previously unexplored region of parameter space. Central to this achievement are the quantum correction terms, which are able to constrain symmetrons with masses in the range $\mu \in [10^{-3.88},10^8]\,\text{eV}$, whereas other experiments have hitherto only been sensitive to one or two orders of magnitude at a time. [Abridged]

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P. Brax, A. Davis, B. Elder, et. al.
Fri, 16 Feb 18
35/42

Comments: 19 pages + appendices, 12 figures. Abstract abridged for arXiv submission

Remote sensing of geomagnetic fields and atomic collisions in the mesosphere [CL]

http://arxiv.org/abs/1802.04686


Magnetic-field sensing has contributed to the formulation of the plate-tectonics theory, the discovery and mapping of underground structures on Earth, and the study of magnetism in other planets. Filling the gap between space-based and near-Earth observation, we demonstrate a novel method for remote measurement of the geomagnetic field at an altitude of 85-100 km. The method consists of optical pumping of atomic sodium in the upper mesosphere with an intensity-modulated laser beam, and simultaneous ground-based observation of the resultant magneto-optical resonance when driving the atomic-sodium spins at the Larmor precession frequency. The experiment was carried out at the Roque de Los Muchachos Observatory in La Palma (Canary Islands) where we validated this technique and remotely measured the Larmor precession frequency of sodium as 260.4(1) kHz, corresponding to a mesospheric magnetic field of 0.3720(1) G. We demonstrate a magnetometry accuracy level of 0.28 mG/$\sqrt{\text{Hz}}$ in good atmospheric conditions. In addition, these observations allow us to characterize various atomic-collision processes in the mesosphere. Remote detection of mesospheric magnetic fields has potential applications such as mapping of large-scale magnetic structures in the lithosphere and the study of electric-current fluctuations in the ionosphere.

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F. Bustos, D. Calia, D. Budker, et. al.
Wed, 14 Feb 18
32/68

Comments: 10 pages, 7 figures

Detailed Opacity Calculations for Stellar Models [SSA]

http://arxiv.org/abs/1802.00782


Radiative opacity is an important quantity in the modeling of stellar structure and evolution. In the present work we recall the role of opacity in the interpretation of pulsations of different kinds of stars. The detailed opacity code SCO-RCG for local-thermodynamic-equilibrium (LTE) plasmas is described, as well as the OPAMCDF project dedicated to the spectroscopy of LTE and non-LTE plasmas. Interpretations, with the latter codes, of several laser and Z pinch experiments in conditions relevant to astrophysical applications are also presented and our work in progress as concerns the internal solar conditions is illustrated.

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J. Pain, F. Gilleron and M. Comet
Mon, 5 Feb 18
31/52

Comments: submitted to ASP Conf. Ser

Searching for stochastic background of ultra-light fields with atomic sensors [CEA]

http://arxiv.org/abs/1801.07577


We propose a cross-correlation method for the searches of ultra-light fields, in particular, with a space network of atomic sensors. The main motivation of the approach is cancellation of uncorrelated noises in the observation data and unique pattern the fields leave on the cross-spectrum, depending on their nature (i.e., scalar, vector or tensor). In particular, we analytically derive a dependence of the cross-spectrum on the angle between two pairs of detectors. We then confirm obtained angular curves with a numerical simulation. We imply application of the method to the detection of dark matter and gravitational waves.

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T. Kalaydzhyan and N. Yu
Wed, 24 Jan 18
27/73

Comments: 16 pages. Comments, including citation requests, are welcome

Stringent constraints on fundamental constant evolution using conjugate 18 cm satellite OH lines [CEA]

http://arxiv.org/abs/1801.07688


We have used the Arecibo Telescope to carry out one of the deepest-ever integrations in radio astronomy, targetting the redshifted conjugate satellite OH 18 cm lines at $z \approx 0.247$ towards PKS1413+135. The satellite OH 1720 and 1612 MHz lines are respectively in emission and absorption, with exactly the same line shapes due to population inversion in the OH ground state levels. Since the 1720 and 1612 MHz line rest frequencies have different dependences on the fine structure constant $\alpha$ and the proton-electron mass ratio $\mu$, a comparison between their measured redshifts allows one to probe changes in $\alpha$ and $\mu$ with cosmological time. In the case of conjugate satellite OH 18 cm lines, the predicted perfect cancellation of the sum of the line optical depths provides a strong test for the presence of systematic effects that might limit their use in probing fundamental constant evolution. A non-parametric analysis of our new Arecibo data yields $\left[\Delta X/X \right] = (+0.97 \pm 1.52) \times 10^{-6}$, where $X \equiv \mu \alpha^2$. Combining this with our earlier results from the Arecibo Telescope and the Westerbork Synthesis Radio Telescope, we obtain $\left[\Delta X/X \right] = (-1.0 \pm 1.3) \times 10^{-6}$, consistent with no changes in the quantity $\mu \alpha^2$ over the last 2.9~Gyr. This is the most stringent present constraint on fractional changes in $\mu \alpha^2$ from astronomical spectroscopy, and with no evidence for systematic effects.

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N. Kanekar, T. Ghosh and J. Chengalur
Wed, 24 Jan 18
47/73

Comments: 5 pages, 2 figures, accepted for publication in Physical Review Letters

Excitation and charge transfer in low-energy hydrogen atom collisions with neutral iron [SSA]

http://arxiv.org/abs/1801.07050


Data for inelastic processes due to hydrogen atom collisions with iron are needed for accurate modelling of the iron spectrum in late-type stars. Excitation and charge transfer in low-energy Fe+H collisions is studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multi-channel Landau-Zener model. An extensive calculation including 166 covalent states and 25 ionic states is presented and rate coefficients are calculated for temperatures in the range 1000 – 20000 K. The largest rates are found for charge transfer processes to and from two clusters of states around 6.3 and 6.6 eV excitation, corresponding in both cases to active 4d and 5p electrons undergoing transfer. Excitation and de-excitation processes among these two sets of states are also significant.

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P. Barklem
Tue, 23 Jan 18
32/85

Comments: Accepted by A&A

The IRON Project: Photoionization of Fe ions [CL]

http://arxiv.org/abs/1801.05410


The IRON Project, initiated in 1991, aims at two main objectives, i) study the characteristics of and calculate large-scale high accuracy data for atomic radiative and collisional processes, and ii) application in solving astrophysical problems. It focuses on the complex iron and iron-peak elements commonly observed in the spectra of astrophysical plasmas. The present report will illustrate the characteristics of the dominant atomic process of photoionization that have been established under the project and the preceding the Opacity Project and their importance in applications.

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S. Nahar
Wed, 17 Jan 18
49/51

Comments: 12 pages, 9 figures, Workshop on Astrophysical Opacities, Western Michigan University, Kalamazoo, Michigan, USA August 1 – 4, 2017

Recalculation of Astrophysical Opacities: Overview, Methodology and Atomic Calculations [SSA]

http://arxiv.org/abs/1801.02085


A review of a renewed effort to recalculate astrophysical opacities using the R-Matrix method is presented. The computational methods and new extensions are described. Resulting enhancements found in test calculations under stellar interior conditions compared to the Opacity Project could potentially lead to the resolution of the solar abundances problem, as well as discrepancies between recent experimental measurements at the Sandia Z-pinch inertial confinement fusion device and theoretical opacity models. Outstanding issues also discussed are: (i) accuracy, convergence, and completeness of atomic calculations, (ii) improvements in the Equation-of-State of high-temperature-density plasmas, and (iii) redistribution of resonant oscillator strength in the bound-free continuum, and (iv) plasma broadening of auotionizing resonances.

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A. Pradhan and S. Nahar
Tue, 9 Jan 18
44/94

Comments: 10 pages, 4 figures, Review, Proc. Workshop on Astrophysical Opacities 2017, PASP

Converged Close-Coupling R-Matrix calculations of Photoionization of Fe XVII in Astrophysical Plasmas: from Convergence to Completeness [SSA]

http://arxiv.org/abs/1801.02188


Extensive resonance structures are manifest in R-Matrix (RM) calculations. However, there exist a large number of highly excited electronic configurations that may contribute to background non-resonant bound-free opacity in high-temperature plasmas. Since RM calculations are very complex, and not essential for background contributions, the Relativistic Distorted Wave (RDW) method is utilized to complement (“top-up”) photoionization cross sections of Fe XVII obtained using Close-Coupling Breit-Pauli R-Matrix (CC-BPRM) method. There is good agreement between RDW and BPRM for background cross sections where resonances are not present, and individual fine structure levels can be correctly matched spectroscopically, though resonances are neglected in the RDW. To ensure completeness, a high energy range up to 500 Ry above the ionization threshold for each level is considered. Interestingly, the hydrogenic Kramer’s approximation also shows the same energy behavior as the RDW. Grouping separately, the BPRM configurations consist of 454 bound levels with resonances corresponding to configurations $1s^22s^22p^4nln’l’$ (n $\leq$ 3, n’ $\leq$ 10); including RDW configurations there are 51,558 levels in total. The topup contribution results in $\sim$20\% increment, in addition to the 35\% enhancement from BPRM calculations over the Opacity Project value for the Rosseland Mean Opacity at the Z-temperature of 2.11 $\times 10^6$K (Pradhan and Nahar 2017).

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L. Zhao, W. Eissner, S. Nahar, et. al.
Tue, 9 Jan 18
59/94

Comments: 5 pages, 2 figures, Proc. Workshop on Astrophysical Opacities 2017, PASP

Polarization of K-shell dielectronic recombination satellite lines of Fe XIX-XXV and its application for diagnostics of anisotropies of hot plasmas [HEAP]

http://arxiv.org/abs/1801.01888


We present a systematic measurement of the X-ray emission asymmetries in the K-shell dielectronic, trielectronic, and quadruelectronic recombination of free electrons into highly charged ions. Iron ions in He-like through O-like charge states were produced in an electron beam ion trap, and the electron-ion collision energy was scanned over the recombination resonances. Two identical X-ray detectors mounted head-on and side-on with respect to the electron beam propagation recorded X-rays emitted in the decay of resonantly populated states. The degrees of linear polarization of X-rays inferred from observed emission asymmetries benchmark distorted-wave predictions of the Flexible Atomic Code (FAC) for several dielectronic recombination satellite lines. The present method also demonstrates its applicability for diagnostics of energy and direction of electron beams inside hot anisotropic plasmas. Both experimental and theoretical data can be used for modeling of hot astrophysical and fusion plasmas.

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C. Shah, P. Amaro, R. Steinbrugge, et. al.
Tue, 9 Jan 18
71/94

Comments: 22 pages, 4 figures, 10 tables, accepted for publication in The Astrophysical Journal Supplement Series

Exotic atoms at extremely high magnetic fields: the case of neutron star atmosphere [CL]

http://arxiv.org/abs/1712.06818


The presence of exotic states of matter in neutron stars (NSs) is currently an open issue in physics. The appearance of muons, kaons, hyperons, and other exotic particles in the inner regions of the NS, favored by energetic considerations, is considered to be an effective mechanism to soften the equation of state (EoS). In the so-called two-families scenario, the softening of the EoS allows for NSs characterized by very small radii, which become unstable and convert into a quark stars (QSs). In the process of conversion of a NS into a QS material can be ablated by neutrinos from the surface of the star. Not only neutron-rich nuclei, but also more exotic material, such as hypernuclei or deconfined quarks, could be ejected into the atmosphere. In the NS atmosphere, atoms like H, He, and C should exist, and attempts to model the NS thermal emission taking into account their presence, with spectra modified by the extreme magnetic fields, have been done. However, exotic atoms, like muonic hydrogen $(p\,\mu^-)$ or the so-called Sigmium $(\Sigma^+\,e^-)$, could also be present during the conversion process or in its immediate aftermath. At present, analytical expressions of the wave functions and eigenvalues for these atoms have been calculated only for H. In this work, we extend the existing solutions and parametrizations to the exotic atoms $(p\,\mu^-)$ and $(\Sigma^+\,e^-)$, making some predictions on possible transitions. Their detection in the spectra of NS would provide experimental evidence for the existence of hyperons in the interior of these stars.

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A. Fontana, A. Colombi, P. Carretta, et. al.
Thu, 21 Dec 17
28/76

Comments: 10 pages, 6 figures, proceedings of the “International Conference on Exotic Atoms and Related Topics – EXA2017”, Austrian Academy of Sciences, Austria, September 11-15, 2017

Vanadium Transitions in the Spectrum of Arcturus [SSA]

http://arxiv.org/abs/1712.06942


We derive a new abundance for vanadium in the bright, mildly metal-poor red giant Arcturus. This star has an excellent high-resolution spectral atlas and well-understood atmospheric parameters, and it displays a rich set of neutral vanadium lines that are available for abundance extraction. We employ a newly recorded set of laboratory FTS spectra to investigate any potential discrepancies in previously reported V I log(gf) values near 900 nm. These new spectra support our earlier laboratory transition data and the calibration method utilized in that study. We then perform a synthetic spectrum analysis of weak V I features in Arcturus, deriving log {\epsilon}(V) = 3.54 $\pm$ 0.01 ({\sigma} = 0.04) from 55 lines. There are no significant abundance trends with wavelength, line strength, or lower excitation energy.

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M. Wood, C. Sneden, J. Lawler, et. al.
Wed, 20 Dec 17
65/83

Comments: Accepted for publication in ApJS; 19 pages, 8 figures, 3 tables

Astrophysical signatures of leptonium [HEAP]

http://arxiv.org/abs/1712.02022


More than 10^43 positrons annihilate every second in the centre of our Galaxy yet, despite four decades of observations, their origin is still unknown. Many candidates have been proposed, such as supernovae and low mass X-ray binaries. However, these models are difficult to reconcile with the distribution of positrons, which are highly concentrated in the Galactic bulge, and therefore require specific propagation of the positrons through the interstellar medium. Alternative sources include dark matter decay, or the supermassive black hole, both of which would have a naturally high bulge-to-disc ratio.
The chief difficulty in reconciling models with the observations is the intrinsically poor angular resolution of gamma-ray observations, which cannot resolve point sources. Essentially all of the positrons annihilate via the formation of positronium. This gives rise to the possibility of observing recombination lines of positronium emitted before the atom annihilates. These emission lines would be in the UV and the NIR, giving an increase in angular resolution of a factor of 10^4 compared to gamma ray observations, and allowing the discrimination between point sources and truly diffuse emission.
Analogously to the formation of positronium, it is possible to form atoms of true muonium and true tauonium. Since muons and tauons are intrinsically unstable, the formation of such leptonium atoms will be localised to their places of origin. Thus observations of true muonium or true tauonium can provide another way to distinguish between truly diffuse sources such as dark matter decay, and an unresolved distribution of point sources.

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S. Ellis and J. Bland-Hawthorn
Thu, 7 Dec 17
1/72

Comments: Accepted for publication in EPJ-D, 9 pages, 4 figures

Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen [SSA]

http://arxiv.org/abs/1712.01166


Excitation and charge transfer in low-energy O+H collisions is studied; it is a problem of importance for modelling stellar spectra and obtaining accurate oxygen abundances in late-type stars including the Sun. The collisions have been studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model. The method has been extended to include configurations involving excited states of hydrogen using an estimate for the two-electron transition coupling, but this extension was found to not lead to any remarkably high rates. Rate coefficients are calculated for temperatures in the range 1000 – 20000 K, and charge transfer and (de)excitation processes involving the first excited S-states, 4s.5So and 4s.3So, are found to have the highest rates.

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P. Barklem
Tue, 5 Dec 17
7/96

Comments: Accepted for A&A. Data will be made available at CDS. Is available here: this https URL

Atomic Interferometric Gravitational-wave Space Observatory (AIGSO) [CL]

http://arxiv.org/abs/1711.03690


We propose a space-borne gravitational-wave detection scheme, called atom interferometric gravitational-wave space observatory (AIGSO). It is motivated by the progress in the atomic matter-wave interferometry, which solely utilizes the standing light waves to split, deflect and recombine the atomic beam. Our scheme consists of three drag-free satellites orbiting the Earth. The phase shift of AIGSO is dominated by the Sagnac effect of gravitational-waves, which is proportional to the area enclosed by the atom interferometer, the frequency and amplitude of gravitational-waves. The scheme has a strain sensitivity $< 10^{-20}/\sqrt{{\rm Hz}}$ in the 100 mHz-10 Hz frequency range, which fills in the detection gap between space-based and ground-based laser interferometric detectors. Thus, our proposed AIGSO can be a good complementary detection scheme to the space-borne laser interferometric schemes, such as LISA. Considering the current status of relevant technology readiness, we expect our AIGSO to be a promising candidate for the future space-based gravitational-wave detection plan.

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D. Gao, J. Wang and M. Zhan
Mon, 13 Nov 17
20/46

Comments: 9 pages, 3 figures

Atomic Interferometric Gravitational-wave Space Observatory (AIGSO) [CL]

http://arxiv.org/abs/1711.03690


We propose a space-borne gravitational-wave detection scheme, called atom interferometric gravitational-wave space observatory (AIGSO). It is motivated by the progress in the atomic matter-wave interferometry, which solely utilizes the standing light waves to split, deflect and recombine the atomic beam. Our scheme consists of three drag-free satellites orbiting the Earth. The phase shift of AIGSO is dominated by the Sagnac effect of gravitational-waves, which is proportional to the area enclosed by the atom interferometer, the frequency and amplitude of gravitational-waves. The scheme has a strain sensitivity $< 10^{-20}/\sqrt{{\rm Hz}}$ in the 100 mHz-10 Hz frequency range, which fills in the detection gap between space-based and ground-based laser interferometric detectors. Thus, our proposed AIGSO can be a good complementary detection scheme to the space-borne laser interferometric schemes, such as LISA. Considering the current status of relevant technology readiness, we expect our AIGSO to be a promising candidate for the future space-based gravitational-wave detection plan.

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D. Gao, J. Wang and M. Zhan
Mon, 13 Nov 17
20/46

Comments: 9 pages, 3 figures

Mid-band gravitational wave detection with precision atomic sensors [IMA]

http://arxiv.org/abs/1711.02225


We assess the science reach and technical feasibility of a satellite mission based on precision atomic sensors configured to detect gravitational radiation. Conceptual advances in the past three years indicate that a two-satellite constellation with science payloads consisting of atomic sensors based on laser cooled atomic Sr can achieve scientifically interesting gravitational wave strain sensitivities in a frequency band between the LISA and LIGO detectors, roughly 30 mHz to 10 Hz. The discovery potential of the proposed instrument ranges from from observation of new astrophysical sources (e.g. black hole and neutron star binaries) to searches for cosmological sources of stochastic gravitational radiation and searches for dark matter.

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P. Graham, J. Hogan, M. Kasevich, et. al.
Wed, 8 Nov 17
12/84

Comments: 18 pages, 4 figures

New method of galactic axion search [CL]

http://arxiv.org/abs/1710.11262


An important and appealing candidate of the galactic dark matter is the axion, which was postulated to solve the CP (Charge-conjugation Parity) violation problem in strong interaction of the standard particle theory. A new experimental method is proposed to determine both the axion mass and its velocity distribution on Earth. The method uses collectively and coherently excited atoms or molecules triggered by strong laser field, resulting in galactic axion absorption along with signal photon emission to be detected.

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M. Yoshimura and N. Sasao
Wed, 1 Nov 17
48/63

Comments: 8 pages, 3 figures

A method for controlling the magnetic field near a superconducting boundary in the ARIADNE axion experiment [CL]

http://arxiv.org/abs/1710.08102


The QCD Axion is a particle postulated to exist since the 1970s to explain the Strong-CP problem in particle physics. It could also account for all of the observed Dark Matter in the universe. The Axion Resonant InterAction DetectioN Experiment (ARIADNE) experiment intends to detect the QCD axion by sensing the fictitious “magnetic field” created by its coupling to spin. The experiment must be sensitive to magnetic fields below the $10^{-19}$ T level to achieve its design sensitivity, necessitating tight control of the experiment’s magnetic environment. We describe a method for controlling three aspects of that environment which would otherwise limit the experimental sensitivity. Firstly, a system of superconducting magnetic shielding is described to screen ordinary magnetic noise from the sample volume at the $10^8$ level. Secondly, a method for reducing magnetic field gradients within the sample up to $10^2$ times is described, using a simple and cost-effective design geometry. Thirdly, a novel coil design is introduced which allows the generation of fields similar to those produced by Helmholtz coils in regions directly abutting superconducting boundaries. The methods may be generally useful for magnetic field control near superconducting boundaries in other experiments where similar considerations apply.

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H. Fosbinder-Elkins, J. Dargert, M. Harkness, et. al.
Tue, 24 Oct 17
48/68

Comments: 8 pages, 11 figures

Progress on the ARIADNE axion experiment [IMA]

http://arxiv.org/abs/1710.05413


The Axion Resonant InterAction Detection Experiment (ARIADNE) is a collaborative effort to search for the QCD axion using techniques based on nuclear magnetic resonance. In the experiment, axions or axion-like particles would mediate short-range spin-dependent interactions between a laser-polarized 3He gas and a rotating (unpolarized) tungsten source mass, acting as a tiny, fictitious “magnetic field”. The experiment has the potential to probe deep within the theoretically interesting regime for the QCD axion in the mass range of 0.1-10 meV, independently of cosmological assumptions. The experiment relies on a stable rotary mechanism and superconducting magnetic shielding, required to screen the 3He sample from ordinary magnetic noise. Progress on testing the stability of the rotary mechanism is reported, and the design for the superconducting shielding is discussed.

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A. Geraci, H. Fosbinder-Elkins, C. Lohmeyer, et. al.
Tue, 17 Oct 17
126/163

Comments: 10 pages, 3 figures, submitted to Proceedings of the 2nd Axion Cavity and Detector Workshop

Charge exchange in galaxy clusters [HEAP]

http://arxiv.org/abs/1710.04784


Though theoretically expected, the charge exchange emission from galaxy clusters has not yet been confidently detected. Accumulating hints were reported recently, including a rather marginal detection with the Hitomi data of the Perseus cluster. As suggested in Gu et al. (2015), a detection of charge exchange line emission from galaxy clusters would not only impact the interpretation of the newly-discovered 3.5 keV line, but also open up a new research topic on the interaction between hot and cold matter in clusters. We aim to perform the most systematic search for the O VIII charge exchange line in cluster spectra using the RGS on board XMM. We introduce a sample of 21 clusters observed with the RGS. The dominating thermal plasma emission is modeled and subtracted with a two-temperature CIE component, and the residuals are stacked for the line search. The systematic uncertainties in the fits are quantified by refitting the spectra with a varying continuum and line broadening. By the residual stacking, we do find a hint of a line-like feature at 14.82 A, the characteristic wavelength expected for oxygen charge exchange. This feature has a marginal significance of 2.8 sigma, and the average equivalent width is 2.5E-4 keV. We further demonstrate that the putative feature can be hardly affected by the systematic errors from continuum modelling and instrumental effects, or the atomic uncertainties of the neighbouring thermal lines. Assuming a realistic temperature and abundance pattern, the physical model implied by the possible oxygen line agrees well with the theoretical model proposed previously to explain the reported 3.5 keV line. If the charge exchange source indeed exists, we would expect that the oxygen abundance is potentially overestimated by 8-22% in previous X-ray measurements which assumed pure thermal lines.

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L. Gu, J. Mao, J. Plaa, et. al.
Mon, 16 Oct 17
25/59

Comments: accepted for publication in A&A