[Paper Review] Comparing solar-system, binary-pulsar, and gravitational-wave tests of gravity

Gilles Esposito-Farèse|ArXiv.org|Mar 15, 1999

Cosmology and Gravitation Theories2 references3 citations

TL;DR

This paper compares the sensitivity of solar-system, binary-pulsar, and gravitational-wave observations to test gravity within tensor-scalar theories. It demonstrates that strong-field tests—especially binary-pulsar data—constrain alternative gravity theories indistinguishable from general relativity in the weak-field solar system, proving that LIGO/Virgo chirp templates can safely be computed in general relativity alone.

ABSTRACT

This talk is based on my work in collaboration with Thibault Damour. We compare the probing power of different classes of gravity experiments: solar-system tests (weak-field regime), binary-pulsar tests (strong-field regime), and future gravitational-wave observations of inspiralling binaries (strong-field effects detected in our weak-gravitational-field conditions). This is done within the most natural class of alternative theories to general relativity, namely tensor-scalar theories, in which the gravitational interaction is mediated by one tensor field (g_munu) together with one or several scalar fields (phi). Our main conclusion is that strong-field tests are qualitatively different from weak-field experiments: They constrain theories which are strictly indistinguishable from general relativity in the solar system. We also show that binary-pulsar data are so precise that they already rule out the theories for which scalar effects could have been detected with LIGO or VIRGO. This proves that it is therefore sufficient to compute the `chirp' templates within general relativity.

Motivation & Objective

• To evaluate the relative probing power of three distinct gravity test regimes: weak-field solar-system experiments, strong-field binary-pulsar systems, and future gravitational-wave observations.
• To assess whether alternative gravity theories—specifically tensor-scalar theories—can be distinguished from general relativity using these different experimental classes.
• To determine whether binary-pulsar observations already constrain scalar-field effects that would otherwise be detectable by ground-based gravitational-wave detectors like LIGO or VIRGO.
• To establish the sufficiency of using general relativity-based chirp templates for gravitational-wave data analysis, given the constraints from strong-field observations.

Proposed method

• Analyzes tensor-scalar gravity theories where gravity is mediated by one symmetric tensor field and one or more scalar fields.
• Uses the parametrized post-Newtonian (PPN) formalism to characterize weak-field solar-system tests.
• Applies post-Keplerian parameter analysis to binary-pulsar systems, focusing on orbital decay and periastron advance.
• Evaluates gravitational-wave signals from inspiralling compact binaries in the context of scalar-tensor theories, particularly the chirp mass and phasing.
• Compares theoretical predictions of scalar effects in each regime against observational bounds from the Hulse-Taylor binary pulsar and future LIGO/VirGO sensitivity.
• Employs numerical and analytical calculations to derive constraints on scalar coupling parameters from each test class.

Experimental results

Research questions

• RQ1 Can binary-pulsar observations rule out scalar-tensor theories that are indistinguishable from general relativity in the solar system?
• RQ2 To what extent do gravitational-wave observations of inspiralling binaries improve constraints on scalar-tensor theories compared to solar-system or binary-pulsar tests?
• RQ3 Are the scalar effects predicted by alternative gravity theories detectable by LIGO or VIRGO, given current binary-pulsar data?
• RQ4 Does the precision of binary-pulsar data make general relativity-based chirp templates sufficient for gravitational-wave data analysis?

Key findings

• Binary-pulsar observations already constrain scalar-tensor theories to the point where scalar effects would not be detectable by LIGO or VIRGO, even if such detectors achieved their design sensitivity.
• Strong-field tests such as those in binary pulsars are qualitatively more powerful than weak-field solar-system tests in distinguishing general relativity from alternative theories.
• Theories that are observationally indistinguishable from general relativity in the solar system are ruled out by binary-pulsar data due to strong-field scalar effects.
• The precision of binary-pulsar data implies that it is sufficient to compute gravitational-wave chirp templates within general relativity, without including scalar-field corrections.
• The constraints from binary-pulsar data are so tight that they exclude the possibility of detecting scalar effects in future gravitational-wave observations with LIGO or VIRGO.