arXiv subjects

A. J. Geddes

Publications and source records attributed to A. J. Geddes.

5 recordsLinked to original sources

arXiv2019

Isotope shifts in $^{20,22}$Ne -- Precision measurements and global analysis in the framework of intermediate coupling

We report new precision measurements of the $^{20}$Ne--$^{22}$Ne isotope shift for several transitions, as well as state-of-the-art, \textit{ab initio} field-shift calculations. Our results are combined with historical measurements in a global fit to obtain the isotope shifts of all fifty low-lying neon levels with high precision. These level shifts show a wealth of electronic, nuclear, and relativistic phenomena. Relying on the analogy between mass shift and fine-structure operators, we explain this plethora of neon level-shifts utilizing a small number of effective parameters in a global parametric investigation. This investigation provides a birds-eye view on the isotope shift phenomena in noble gasses. From this vantage point, we reinterpret every effort made to calculate neon mass-shifts \textit{ab initio}, and show that a remarkable agreement between experiment and theory is obtained.

physics.atom-ph↗

arXiv2018

Saturated configuration interaction calculations for five-valent Ta and Db

Accurate atomic structure calculations of complicated atoms with 4 or more valence electrons begin to push the memory and time limits of supercomputers. This paper presents a robust method of decreasing the size of \textit{ab initio} configuration interaction and many-body perturbation theory calculations without undermining the accuracy of the resulting atomic spectra. Our method makes it possible to saturate the CI matrix in atoms with many valence electrons. We test our method on the five-valence-electron atom tantalum and verify the convergence of the calculated energies. We then apply the method to calculate spectra and isotope shifts of tantalum's superheavy analogue dubnium. Isotope-shift calculations can be used to predict the spectra of superheavy isotopes which may be produced in astrophysical phenomena.

physics.atom-ph↗

arXiv2018

Enhanced nuclear spin dependent parity violation effects using the 199HgH molecule

Electron interactions with the nuclear-spin-dependent (NSD) parity non-conserving (PNC) anapole moment are strongly enhanced within heteronuclear diatomic molecules. A novel, low-energy optical rotation experiment is being proposed with the aim of observing NSD PNC interactions in HgH. Based on the relativistic coupled cluster method we present a complete calculation of the circular polarization parameter $P = 2\,\textrm{Im}(E1_{PNC})/M1 \approx 3 \times 10^{-6}\; κ$ for the $^2Σ_{1/2} \to ^2Π_{1/2}$ optical transition of HgH, where $κ$ is a dimensionless constant determined by the nuclear anapole moment. This provides an improvement in sensitivity to NSD PNC by 2 -- 3 orders of magnitude over the leading atomic Xe, Hg, Tl, Pb and Bi optical rotation experiments, and shows that the proposed measurement will be sensitive enough to extract the $^{199}$Hg anapole moment and shed light on the underlying theory of hadronic parity violation.

physics.atom-ph↗

arXiv2018

Isotope shift, non-linearity of King plots and the search for new particles

We derive a mean-field relativistic formula for the isotope shift of an electronic energy level for arbitrary angular momentum; we then use it to predict the spectra of superheavy metastable neutron-rich isotopes belonging to the hypothetical island of stability. Our results may be applied to the search for superheavy atoms in astrophysical spectra using the known values of the transition frequencies for the neutron deficient isotopes produced in the laboratory. An example of a relevant astrophysical system may be the spectra of the Przybylski's star where superheavy elements up to Z=99 have been possibly identified. In addition, it has been recently suggested to use the measurements of King plot non-linearity in a search for hypothetical new light bosons. On the other hand, one can find the non-linear corrections to the King-plot arising already in the Standard Model framework. We investigate contributions to the non-linearity arising from relativistic effects in the isotope field-shift, the nuclear polarizability and many-body effects. It is found that the nuclear polarizability contribution can lead to the significant deviation of the King plot from linearity. Therefore, the measurements of the non-linearity of King plots may be applied to obtain the nuclear polarizability change between individual isotopes. We then proceed with providing a rough analytical estimate of the non-linearity arising solely from the effect of a hypothetical scalar boson. Our predictions give theoretical limitations on the sensitivity of the search for new interactions and should help to identify the most suitable atoms for corresponding experiments.

physics.atom-ph↗

arXiv2005

Novel Dynamical Resonances in Finite-Temperature Bose-Einstein Condensates

We describe a variety of intriguing mode-coupling effects which can occur in a confined Bose-Einstein condensed system at finite temperature. These arise from strong interactions between a condensate fluctuation and resonances of the thermal cloud yielding strongly non-linear behaviour. We show how these processes can be affected by altering the aspect ratio of the trap, thereby changing the relevant mode-matching conditions. We illustrate how direct driving of the thermal cloud can lead to significant shifts in the excitation spectrum for a number of modes and provide further experimental scenarios in which the dramatic behaviour observed for the $m=0$ mode at JILA (Jin {\it et al.} 1997) can be repeated. Our theoretical description is based on a successful second-order finite-temperature quantum field theory which includes the full coupled dynamics of the condensate and thermal cloud and all relevant finite-size effects.

cond-mat.stat-mech↗