Probing the Higher Redshift Universe by Studying Strong Lensing of Gravitational Waves and Enhancing Search Sensitivity of the GstLAL Search Pipeline

Citation

Li, Ka Yue Alvin (2024) Probing the Higher Redshift Universe by Studying Strong Lensing of Gravitational Waves and Enhancing Search Sensitivity of the GstLAL Search Pipeline. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/hc11-h960. https://resolver.caltech.edu/CaltechTHESIS:05242024-202843732

Abstract

The LIGO-Virgo-KAGRA (LVK) collaboration first observed gravitational waves in 2015, and more than $90$ gravitational-wave events have been observed, all coming from mergers of compact objects (black holes and neutron stars), known as compact binary coalescences (CBC). Studying and observing gravitational waves opens a new window for us to understand the nature of spacetime and the universe. Strain data from LVK's detectors are analyzed by search pipelines to identify weak gravitational-wave signals in noisy data. To maximize the potential of gravitational waves, it is essential to continue to improve search pipelines' sensitivity to probe GW sources with the broadest range of parameters and from the furthest distances. I will give a detailed overview of the GstLAL pipeline and present related development (ongoing) work for GstLAL to enhance its search effectiveness and efficiency.

In the second part of my thesis, I will focus on gravitational lensing of gravitational waves. As masses can produce curvature in spacetime, gravitational waves, like electromagnetic (EM) waves, are deflected when passing by massive intervening objects before reaching gravitational-wave detectors on Earth, an effect known as gravitational lensing. Observing lensed gravitational waves confirms another prediction in Einstein's general relativity and enables us to conduct cosmography studies, test general relativity, search for dark matter and other exotic phenomena, and deepen our understanding of the universe. I will give a detailed introduction to gravitational lensing of gravitational waves. We then introduce a Targeted subthreshold search for strongly-lensed gravitational wave pipeline called "TESLA". The TESLA pipeline is the flagship to look for sub-threshold lensed gravitational waves. Next, we present the results of the LVK collaboration-wide effort to search for lensing signatures in gravitational-wave data from the third observing run O3. Next, we introduce a significant update to the TESLA pipeline, now known as the TESLA-X pipeline, with enhanced search sensitivity towards lensed gravitational waves. We also introduce an alternative ranking statistic implemented into the TESLA-X pipeline that considers the signal's consistency with the assumed lens model. Finally, we end the thesis with a summary and an outline of possible future work.

Thesis Files