On the shortcomings of the Shapiro delay tests of the equivalence principle

TL;DR

This paper critiques the limitations of standard Shapiro delay tests for the equivalence principle on cosmological scales, highlighting unresolved issues despite existing alternative proposals.

Contribution

It identifies specific shortcomings in current Shapiro delay tests and emphasizes the need for improved methods in testing the equivalence principle cosmologically.

Findings

Standard tests have significant limitations on cosmological scales

Existing alternative methods are acknowledged but not widely adopted

The paper calls for more robust testing approaches

Abstract

There are several shortcomings in the "standard" Shapiro delay tests of the equivalence principle on cosmological scales \cite{minazzoli:2019pr}. Although many people in the community already acknowledged this in the literature, and proposed alternative ways to compare potential Shapiro delays over cosmological scales -- e.g. \cite{bartlett:2021pr,hashimoto:2021pr} and references therein -- papers are still submitted to journals with the usual issues.