Bounds on Lorentz and CPT violation from the $1S$-$2P$ transition in antihydrogen

TL;DR

This work uses the Standard Model Extension to model Lorentz- and CPT-violating frequency shifts in the antihydrogen $1S$-$2P$ transition measured by ALPHA in a $1\,\mathrm{T}$ magnetic field. By deriving the laboratory-frame perturbations from NR SME coefficients for both the positron and antiproton and transforming to the Sun-centered frame, the authors identify constant and sidereal contributions to the transition frequencies. Comparing the constant Sun-frame shifts to ALPHA’s agreement between theory and experiment yields the first bounds on 26 NR coefficients, including those with $j>1$, inaccessible to more common antihydrogen transitions. The study highlights the value of measuring multiple, high-angular-momentum transitions to test CPT symmetry and discusses future improvements via deuterium and other transitions to further tighten these bounds.

Abstract

A model for the Lorentz- and CPT-violating frequency shift for the antihydrogen $1S$-$2P$ transition in the presence of an external magnetic field is derived. Using the recent measurement of the $1S$-$2P$ transition frequency in antihydrogen by the ALPHA collaboration, which they demonstrated agrees with predictions from the Standard Model of particle physics, we establish the first constraints on 26 effective coefficients for Lorentz and CPT violation. Also, this work uses these results to underscore the value of measuring multiple transition frequencies to test CPT symmetry through antihydrogen spectroscopy, emphasizing the advantages of transitions involving states with higher angular momentum.