Frequency shift up to the 2-PM approximation

TL;DR

This paper advances the calculation of frequency shifts of electromagnetic signals in gravitational fields using the time transfer function formalism up to the 2-PM approximation, simplifying complex geodesic integrations.

Contribution

It introduces a new formulation for one-way frequency shift calculations up to the post-post-Minkowskian level using the time transfer function approach.

Findings

Simplifies frequency shift calculations in gravitational fields.

Provides explicit expressions up to 2-PM approximation.

Reduces computational complexity compared to geodesic integration.

Abstract

A lot of fundamental tests of gravitational theories rely on highly precise measurements of the travel time and/or the frequency shift of electromagnetic signals propagating through the gravitational field of the Solar System. In practically all of the previous studies, the explicit expressions of such travel times and frequency shifts as predicted by various metric theories of gravity are derived from an integration of the null geodesic differential equations. However, the solution of the geodesic equations requires heavy calculations when one has to take into account the presence of mass multipoles in the gravitational field or the tidal effects due to the planetary motions, and the calculations become quite complicated in the post-post-Minkowskian approximation. This difficult task can be avoided using the time transfer function's formalism. We present here our last advances in the formulation of the one-way frequency shift using this formalism up to the post-post-Minkowskian approximation.