Lorentz and CPT Tests with Clock-Comparison Experiments

TL;DR

This paper analyzes clock-comparison experiments to test Lorentz and CPT symmetry, characterizing signals from potential violations and interpreting experimental results to set bounds on Lorentz-violating coefficients across various atomic and subatomic systems.

Contribution

It develops a comprehensive theoretical framework for interpreting clock-comparison experiments in terms of Lorentz and CPT violation, including nonminimal operators and diverse experimental setups.

Findings

Established bounds on nonminimal Lorentz-violating coefficients in the neutron sector.

Demonstrated the sensitivity of various clock experiments to Lorentz and CPT violation.

Provided estimates for future experimental sensitivities.

Abstract

Clock-comparison experiments are among the sharpest existing tests of Lorentz symmetry in matter. We characterize signals in these experiments arising from modifications to electron or nucleon propagators and involving Lorentz- and CPT-violating operators of arbitrary mass dimension. The spectral frequencies of the atoms or ions used as clocks exhibit perturbative shifts that can depend on the constituent-particle properties and can display sidereal and annual variations in time. Adopting an independent-particle model for the electronic structure and the Schmidt model for the nucleus, we determine observables for a variety of clock-comparison experiments involving fountain clocks, comagnetometers, ion traps, lattice clocks, entangled states, and antimatter. The treatment demonstrates the complementarity of sensitivities to Lorentz and CPT violation among these different experimental techniques. It also permits the interpretation of some prior results in terms of bounds on nonminimal coefficients for Lorentz violation, including first constraints on nonminimal coefficients in the neutron sector. Estimates of attainable sensitivities in future analyses are provided. Two technical appendices collect relationships between spherical and cartesian coefficients for Lorentz violation and provide explicit transformations converting cartesian coefficients in a laboratory frame to the canonical Sun-centered frame.