Doubly-differential cross section calculations for KK-shell vacancy production in lithium by fast O8+^{8+} ion impact

Inner-shell vacancy production for the O$^{8+}$-Li collision system at 1.5 MeV/amu is studied theoretically. The theory combines single-electron amplitudes for each electron in the system to extract multielectron information about the collision process. Doubly-differential cross sections obtained in this way are then compared with the recent experimental data by LaForge et al. [J. Phys. B 46, 031001 (2013)] yielding good resemblance, especially for low outgoing electron energy. A careful analysis of the processes that contribute to inner-shell vacancy production shows that the improvement of the results as compared to single-active-electron calculations can be attributed to the leading role of two-electron excitation-ionization processes

Oriented polar molecules in a solid inert-gas matrix: a proposed method for measuring the electric dipole moment of the electron

We propose a very sensitive method for measuring the electric dipole moment of the electron using polar molecules embedded in a cryogenic solid matrix of inert-gas atoms. The polar molecules can be oriented in the $\hat{\rm{z}}$ direction by an applied electric field, as has recently been demonstrated by Park, et al. [Angewandte Chemie {\bf 129}, 1066 (2017)]. The trapped molecules are prepared into a state which has its electron spin perpendicular to $\hat{\rm{z}}$, and a magnetic field along $\hat{\rm{z}}$ causes precession of this spin. An electron electric dipole moment $d_e$ would affect this precession due to the up to 100~GV/cm effective electric field produced by the polar molecule. The large number of polar molecules that can be embedded in a matrix, along with the expected long coherence times for the precession, allows for the possibility of measuring $d_e$ to an accuracy that surpasses current measurements by many orders of magnitude. Because the matrix can inhibit molecular rotations and lock the orientation of the polar molecules, it may not be necessary to have an electric field present during the precession. The proposed technique can be applied using a variety of polar molecules and inert gases, which, along with other experimental variables, should allow for careful study of systematic uncertainties in the measurement

Inflating in a Trough: Single-Field Effective Theory from Multiple-Field Curved Valleys

We examine the motion of light fields near the bottom of a potential valley in a multi-dimensional field space. In the case of two fields we identify three general scales, all of which must be large in order to justify an effective low-energy approximation involving only the light field, $\ell$. (Typically only one of these -- the mass of the heavy field transverse to the trough -- is used in the literature when justifying the truncation of heavy fields.) We explicitly compute the resulting effective field theory, which has the form of a $P(\ell,X)$ model, with $X = - 1/2(\partial \ell)^2$, as a function of these scales. This gives the leading ways each scale contributes to any low-energy dynamics, including (but not restricted to) those relevant for cosmology. We check our results with the special case of a homogeneous roll near the valley floor, placing into a broader context recent cosmological calculations that show how the truncation approximation can fail. By casting our results covariantly in field space, we provide a geometrical criterion for model-builders to decide whether or not the single-field and/or the truncation approximation is justified, identify its leading deviations, and to efficiently extract cosmological predictions.Comment: 28 pages + 3 appendices, references added and typos corrected, matches published versio

Positron-rubidium scattering

A 5-state close-coupling calculation (5s-5p-4d-6s-6p) was carried out for positron-Rb scattering in the energy range 3.7 to 28.0 eV. In contrast to the results of similar close-coupling calculations for positron-Na and positron-K scattering the (effective) total integrated cross section has an energy dependence which is contrary to recent experimental measurements

Fitting for the energy levels of hydrogen

Atomic hydrogen energy levels calculated to high precision are required to assist experimental researchers working on spectroscopy in the pursuit of testing quantum electrodynamics (QED) and probing for physics beyond the Standard Model. There are two important parts to the problem of computing these levels: an accurate evaluation of contributions from QED and using an accurate value for the proton charge radius as an input. Recent progress on QED corrections to the fine structure, as well as increasing evidence that a proton charge radius in the range of 0.84 fm is favored over the previously adopted larger value in the 0.88 fm range, has advanced the field, yet several state-of-the-art measurements remain in contradiction with this smaller value. Motivated by on-going and future work in this area, we present here a simple parameterization for the energy levels of hydrogen at the level of hyperfine structure using the so-called relativistic Ritz approach. The fitting of a finite sample of QED-generated levels at low to intermediate principal quantum number, $n$, gives a generally applicable formula for \emph{all} values of $n$ for each distinct angular momentum channel, given in this work up to orbital angular momentum number $\ell=30$. We also provide a simple linear parameterization for the shift in hydrogen energy levels as a function of the proton radius, providing a useful cross check for extant and future measured energy intervals.Comment: 6 pages of main text, 3 figures. Accepted by J. Phys.

Resonances in low-energy positron-alkali scattering

Close-coupling calculations were performed with up to five target states at energies in the excitation threshold region for positron scattering from Li, Na and K. Resonances were discovered in the L = 0, 1 and 2 channels in the vicinity of the atomic excitation thresholds. The widths of these resonances vary between 0.2 and 130 MeV. Evidence was found for the existence of positron-alkali bound states in all cases