Higher order test of Lorentz invariance with an optical ring cavity

TL;DR

This study used an optical ring cavity over a year to test Lorentz invariance in photons, finding no anisotropy at the level of 10^{-15} and setting new limits on higher-order violations.

Contribution

The paper introduces a novel optical ring cavity setup and analysis method to test higher-order Lorentz violation with improved sensitivity and first-time limits on hexapole components.

Findings

No evidence of light speed anisotropy at δc/c ≲ 10^{-15}

Limits on dipole anisotropy components improved by over an order of magnitude

First constraints on hexapole anisotropy components

Abstract

We have developed an apparatus to search for the higher-order Lorentz violation in photons by measuring the resonant frequency difference between two counterpropagating directions of an asymmetric optical ring cavity. From the year-long data taken between 2012 and 2013, we found no evidence for the light speed anisotropy at the level of $\delta c/c \lesssim 10^{-15}$. Limits on the dipole components of the anisotropy are improved by more than an order of magnitude, and limits on the hexapole components are obtained for the first time. An overview of our apparatus and the data analysis in the framework of the spherical harmonics decomposition of anisotropy are presented. We also present the status of the recent upgrade of the apparatus.