Octupolar test of general relativity

Parthapratim Mahapatra

arXiv:2306.04703v2 Announce Type: replace-cross

Abstract: Compact binaries with unequal masses and whose orbits are not aligned with the observer’s line of sight are excellent probes of gravitational radiation beyond the quadrupole approximation. Among the compact binaries observed so far, strong evidence of octupolar modes is seen in GW190412 and GW190814, two binary black holes observed during the first half of the third observing run of LIGO/Virgo observatories. These two events, therefore, provide a unique opportunity to test the consistency of the octupolar modes with the predictions of general relativity (GR). In the post-Newtonian (PN) approximation to GR, the gravitational-wave phasing has known dependencies on different radiative multipole moments, including the mass octupole. This permits the use of publicly released posteriors of the PN phase deformation parameters for placing constraints on the deformations to the different PN components of the radiative mass octupole denoted by $delta mu_{3n}$. Combining the posteriors on $delta mu_{3n}$ from these two events, we deduce a joint bound (at 90% credibility) on the first three PN order terms in the radiative octupoles to be $delta mu_{30}=-0.07^{+0.11}_{-0.12}$, $delta mu_{32}=0.48^{+0.93}_{-1.15}$, and $delta mu_{33}=-0.32^{+1.67}_{-0.62}$, consistent with GR predictions. Among these, the measurement of $delta mu_{33}$ for the first time confirms the well-known octupolar tail contribution, a novel nonlinear effect due to the scattering of the octupolar radiation by the background spacetime, is consistent with the predictions of GR. Detection of similar systems in the future observing runs should further tighten these constraints.arXiv:2306.04703v2 Announce Type: replace-cross

Abstract: Compact binaries with unequal masses and whose orbits are not aligned with the observer’s line of sight are excellent probes of gravitational radiation beyond the quadrupole approximation. Among the compact binaries observed so far, strong evidence of octupolar modes is seen in GW190412 and GW190814, two binary black holes observed during the first half of the third observing run of LIGO/Virgo observatories. These two events, therefore, provide a unique opportunity to test the consistency of the octupolar modes with the predictions of general relativity (GR). In the post-Newtonian (PN) approximation to GR, the gravitational-wave phasing has known dependencies on different radiative multipole moments, including the mass octupole. This permits the use of publicly released posteriors of the PN phase deformation parameters for placing constraints on the deformations to the different PN components of the radiative mass octupole denoted by $delta mu_{3n}$. Combining the posteriors on $delta mu_{3n}$ from these two events, we deduce a joint bound (at 90% credibility) on the first three PN order terms in the radiative octupoles to be $delta mu_{30}=-0.07^{+0.11}_{-0.12}$, $delta mu_{32}=0.48^{+0.93}_{-1.15}$, and $delta mu_{33}=-0.32^{+1.67}_{-0.62}$, consistent with GR predictions. Among these, the measurement of $delta mu_{33}$ for the first time confirms the well-known octupolar tail contribution, a novel nonlinear effect due to the scattering of the octupolar radiation by the background spacetime, is consistent with the predictions of GR. Detection of similar systems in the future observing runs should further tighten these constraints.

2024-10-10