Tests of scalar polarizations with multi-messenger events

Sk Md Adil Imam; Macarena Lagos

doi:10.1103/f9ll-y1rn

paper

Tests of scalar polarizations with multi-messenger events

arXiv:2604.24526 · doi:10.1103/f9ll-y1rn

Abstract

Gravitational wave (GW) observations provide a unique opportunity to test Einstein's General Relativity (GR) in the strong-field regime. While GR predicts only two tensor polarization modes, generic metric theories allow up to six independent modes. We perform a parameterized test of GR using the parameterized post-Einsteinian (PPE) framework applied to GW170817, incorporating for the first time the polarization angle constraints from the gamma-ray burst afterglow alongside other electromagnetic (EM) counterpart information. We extend the GR waveform by adding a scalar breathing mode and modifications to the tensor modes, introducing three non-GR parameters. We perform Bayesian inference for both quadrupole $ℓ = ∣ m ∣ = 2$ and dipole $ℓ = ∣ m ∣ = 1$ angular harmonics, with two frequency evolution models. For $ℓ = ∣ m ∣ = 2$ , we find that within the extended PPE framework the scalar amplitude deviates from zero at the $2$ -- $3 σ$ level, leading to a modest preference for modified gravity. However, due to penalization of extra parameters, Bayesian model comparison still favors pure GR over the extended PPE waveform model, with a log Bayes factor of $Δ lo g Z = 4.67 \pm 0.32$ . The EM constraint on the polarization angle places very tight bounds on non-GR parameters; for instance, in the case $ℓ = ∣ m ∣ = 2$ , the bound on the scalar (tensor) amplitude modification parameter improves by roughly $60%$ $(30%)$ , highlighting the impact that long-term follow up of GW events can have on tests of gravity.

16 pages, 12 figures

Tests of scalar polarizations with multi-messenger events

Abstract

References in corpus (55)