Stealth Bias in Gravitational-Wave Parameter Estimation

TL;DR

This paper investigates the potential for undetectable systematic errors, called stealth bias, in gravitational-wave source parameter estimation caused by deviations from General Relativity, which could affect future observations.

Contribution

It develops a scheme to identify when stealth bias may occur in gravitational-wave data analysis, considering the effects of modified gravity theories on parameter estimation.

Findings

Stealth bias can significantly affect parameter estimates without detectable signals of modified gravity.

The bias depends on signal-to-noise ratio and the strength of deviations from General Relativity.

Stealth bias may be common in gravitational-wave detections and should be accounted for in data analysis.

Abstract

Inspiraling binaries of compact objects are primary targets for current and future gravitational-wave observatories. Waveforms computed in General Relativity are used to search for these sources, and will probably be used to extract source parameters from detected signals. However, if a different theory of gravity happens to be correct in the strong-field regime, source-parameter estimation may be affected by a fundamental bias: that is, by systematic errors induced due to the use of waveforms derived in the incorrect theory. If the deviations from General Relativity are not large enough to be detectable on their own and yet these systematic errors remain significant (i.e., larger than the statistical uncertainties in parameter estimation), fundamental bias cannot be corrected in a single observation, and becomes stealth bias. In this article we develop a scheme to determine in which cases stealth bias could be present in gravitational-wave astronomy. For a given observation, the answer depends on the detection signal-to-noise ratio and on the strength of the modified-gravity correction. As an example, we study three representative stellar-mass binary systems that will be detectable with second-generation ground-based observatories. We find that significant systematic bias can occur whether or not modified gravity can be positively detected, for correction strengths that are not currently excluded by any other experiment. Thus, stealth bias may be a generic feature of gravitational-wave detections, and it should be considered and characterized, using expanded models such as the parametrized post-Einstein framework, when interpreting the results of parameter-estimation analyses.