On parametric tests of relativity with false degrees of freedom

TL;DR

This paper critically examines the use of artificial degrees of freedom in testing general relativity with gravitational wave data, highlighting logical issues and limitations of current methods.

Contribution

It identifies key pitfalls in parametric tests of relativity that incorporate artificial degrees of freedom, questioning their interpretability and effectiveness.

Findings

Artificial degrees of freedom complicate the interpretation of constraints.

Bayesian model comparison may not validate general relativity effectively.

Tests with available waveforms are more reliable for alternative theories.

Abstract

General relativity can be tested by comparing the binary-inspiral signals found in LIGO--Virgo data against waveform models that are augmented with artificial degrees of freedom. This approach suffers from a number of logical and practical pitfalls. 1) It is difficult to ascribe meaning to the stringency of the resultant constraints. 2) It is doubtful that the Bayesian model comparison of relativity against these artificial models can offer actual validation for the former. 3) It is unknown to what extent these tests might detect alternative theories of gravity for which there are no computed waveforms; conversely, when waveforms are available, tests that employ them will be superior.