Non-linear isotope-shift effects in Be-like, B-like, and C-like argon

TL;DR

This paper investigates non-linear isotope-shift effects in argon ions, revealing larger-than-expected deviations in King plots due to Standard Model contributions, which are crucial for detecting new physics.

Contribution

The study provides the first systematic large-scale relativistic calculations of quadratic mass and field shifts in argon ions, highlighting significant non-linearities in isotope shifts.

Findings

Nonlinearities of 5 to 30 kHz in King plots were observed.

Nonlinear effects are four orders of magnitude larger than previous estimates.

Accurate modeling of these effects is essential for new physics searches.

Abstract

Violation of linearity of the King plot is investigated for a chain of partially stripped argon isotopes. The nonlinearity originates within the Standard Model from subtle contributions to the isotope shifts from next-to-leading order effects, which have never been systematically studied so far. In light atoms these nonlinear effects are dominated by the quadratic nuclear recoil ($\propto 1/M^2$ where $M$ is the nuclear mass). Large-scale relativistic calculations of the linear and quadratic mass shift and the field shift are performed for the $2P$ fine-structure transitions in Be-like, B-like, and C-like argon ions. Nonlinearities of the King plots from 5 to 30 kHz are found, which is four orders of magnitude larger than previous estimates in comparable systems. Accurate calculations of these effects are vital for identification of possible nonlinearities originating from physics beyond the Standard Model.