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

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

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

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

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

Comments: 10 pages, 7 figures

Detailed Opacity Calculations for Stellar Models [SSA]

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

Comments: submitted to ASP Conf. Ser

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

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

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

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

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

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]

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

Comments: Accepted by A&A

The IRON Project: Photoionization of Fe ions [CL]

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

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