Lorentz symmetry and Very Long Baseline Interferometry

TL;DR

This paper derives VLBI observables within the SME framework, analyzes decades of data, and sets a new, tighter constraint on Lorentz symmetry violation in gravity.

Contribution

It introduces a method to test Lorentz symmetry violations using VLBI data within the SME framework, improving previous constraints.

Findings

Constraint on $ar s^{TT}$ improved to $(-5 ext{±}8) imes 10^{-5}$

Analysis of data since 1979 with various schemes

VLBI observables derived and implemented in analysis code

Abstract

Lorentz symmetry violations can be described by an effective field theory framework that contains both General Relativity and the Standard Model of particle physics called the Standard-Model extension (SME). Recently, post-fit analysis of Gravity Probe B and binary pulsars lead to an upper limit at the $10^{-4}$ level on the time-time coefficient $\bar s^{TT}$ of the pure-gravity sector of the minimal SME. In this work, we derive the observable of Very Long Baseline Interferometry (VLBI) in SME and then we implement it into a real data analysis code of geodetic VLBI observations. Analyzing all available observations recorded since 1979, we compare estimates of $\bar s^{TT}$ and errors obtained with various analysis schemes, including global estimations over several time spans and with various Sun elongation cut-off angles, and with analysis of radio source coordinate time series. We obtain a constraint on $\bar s^{TT}=(-5\pm 8)\times 10^{-5}$, directly fitted to the observations and improving by a factor 5 previous post-fit analysis estimates.