Search

Leveraging the features of the GstLAL pipeline, we present the results of a matched filtering search for asymmetric binary black hole systems with heavily mis-aligned spins in LIGO and Virgo data taken during the third observing run. Our target systems show strong imprints of precession and current searches have non-optimal sensitivity in detecting them. After measuring the sensitivity improvement brought by our search over standard spin-aligned searches, we report the detection of 30 gravitational wave events already discovered in the latest Gravitational Wave Transient Catalogues. However, we do not find any additional significant gravitational wave candidates. Our results allow us to place an upper limit of $R_{90\%} = 0.28^{+0.33}_{-0.04}\;\; \mathrm{Gpc^{-3}yr^{-1}}$ on the merger rate of a hypothetical subpopulation of asymmetric, heavily precessing signals, not identified by other searches. Since our upper limit is consistent with the latest rate estimates from the LIGO-Virgo-KAGRA collaboration, our findings rule out the existence of a yet-to-be-discovered population of precessing binaries.

The standard cosmological model involves the assumption of isotropy and homogeneity, a principle that is generally well-motivated but is now in conflict with various anisotropies found using independent astrophysical probes. These anisotropies tend to take the form of dipoles; while some can be explained by simple kinematic effects, many others are not fully understood. Thus, generic phenomenological models are being considered, such as a dipole in the luminosity distance. We demonstrate how such a dipole could be measured using gravitational waves from binary neutron star mergers observed by six different networks of gravitational-wave detectors, ranging from upgraded LIGO detectors to anticipated next-generation ground-based observatories. We find that, for example, a network of three next-generation detectors would produce strong constraints on a dipole's amplitude ($\sim 13\%$) and location ($\sim 84$ deg$^2$) after just one year of observing. We demonstrate that the constraints scale with the number of detections, enabling projections for multiple years of observing. Our findings indicate that future observations of binary neutron star mergers would improve upon existing dipole constraints, provided that at least one next-generation detector is built. We also assess directional sensitivity of the dipole measurements by varying the dipole's location on a grid across the sky. We find that for a network of three next-generation detectors, the range of the constraints is only $\lesssim 1.2\%$ for the amplitude and $\lesssim 4\%$ for the location, indicating that the location of the dipole will not greatly impact our ability to measure its effects., Comment: 18 pages, 9 figures

Precession in Binary Black Holes (BBH) is caused by the failure of the Black Hole spins to be aligned and its study can open up new perspectives in gravitational waves (GW) astronomy, providing, among other advancements, a precise measure of distance and an accurate characterization of the BBH spins. However, detecting precessing signals is a highly non-trivial task, as standard matched filtering pipelines for GW searches are built on many assumptions that do not hold in the precessing case. This work details the upgrades made to the GstLAL pipeline to facilitate the search for precessing BBH signals. The implemented changes in the search statistics and in the signal consistency test are then described in detail. The performance of the upgraded pipeline is evaluated through two extensive searches of precessing signals, targeting two different regions in the mass space, and the consistency of the results is examined. Additionally, the benefits of the upgrades are assessed by comparing the sensitive volume of the precessing searches with two corresponding traditional aligned-spin searches. While no significant sensitivity improvement is observed for precessing binaries with mass ratio $q\lesssim 6$, a volume increase of up to 100\% is attainable for heavily asymmetric systems with largely misaligned spins. Furthermore, our findings suggest that the primary cause of degraded performance in an aligned-spin search targeting precessing signals is not a poor signal-to-noise-ratio recovery but rather the failure of the $\xi^2$ signal-consistency test. Our work paves the way for a large-scale search for precessing signals, which could potentially result in exciting future detections.