A robust test of general relativity at the galactic scales by combining strong lensing systems and gravitational wave standard sirens
Physical Review D(2024)
摘要
The measurement of the parametrized post-Newtonian parameter
γ_PPN is a robust test of general relativity (GR). In some
modified theories of gravity, γ_PPN may evolve with the redshift
and deviate from one at high redshifts. This means that precise constraints on
γ_PPN acquired in the solar system experiments could not be
sufficient to test such theories and it is necessary to constrain
γ_PPNwith high precision at high redshifts. However, in many
approaches aimed at extragalactic tests of GR, the results might be biased due
to entanglement of various factors, such as cosmic curvature, cosmic opacity,
and the Hubble constant. Strong lensing systems naturally provide a laboratory
to test γ_PPN at galactic scales and high redshifts, but there is
degeneracy between measured strength of gravity and cosmic distances in the
lensing system. Gravitational waves (GWs) from binary neutron star mergers
(standard sirens) provide a direct way to break this degeneracy by providing
self-calibrated measurements of the luminosity distance. We investigate the
possibility of estimating γ_PPN by combining well measured
strongly lensed systems with GW signals from coalescing neutron stars. Such
combination provides a cosmological-model independent, relatively pure and
unbiased method for the inference of γ_PPN parameter, avoiding
the influence of the above factors and the mass-sheet degeneracy in the lens.
Based on the simulated future 55 lensed quasar systems we demonstrated that the
precision of γ_PPN parameter obtained by our method could be of
order of ∼ 10^-2. One may reasonably expect that our approach will play
an increasingly important role in precise testing the validity of general
relativity at galactic scales and high redshifts.
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