Search for subsolar mass black holes in LIGO/Virgo using O3 data and the implementation of Machine Learning algorithms in the identification of Compact Binary Coalescence events

Abstract

Gravitational waves have been theorized by General relativity since 1916 but it was not until September 14th 2015 that a confirmed detection was made by the LIGO interferometers. Since then, about 90 gravitational wave events have been detected by the LIGO and Virgo interferometers. This was made possible not only due to the increase in sensitivity of the interferometer network, but also due to our rising understanding of the population sources and noise distribution. Gravitational waves provide a new window into the universe and our understanding of black holes. In particular, they allow us to probe different mass regions, as for example, the subsolar mass range. Even though no event has been detected in this range, a possible detection would imply potential new physics and new formation channels. The detected events have been produced by the coalescence of two compact objects (Black holes or neutron stars) and were detected by means of dedicated search pipelines. These pipelines use a technique, known as matched filter, that searches the data by correlating it with a set of theoretical waveforms describing the gravitational waves. The efficacy of this method is limited by the computational resources available, as it requires a dense sampling of the searched parameter space. Nevertheless, the matched filter technique remains as a robust approach for the detection of gravitational waves. The results of this thesis are divided into two parts: First, we present the results of the subsolar mass search carried out within the collaboration using the third observation run and matched filter. We will focus on two possible formation channels of subsolar black holes: primordial black holes and dark matter black holes, and provide limits to their abundance in the universe. Second, we design a machine learning technique for the detection of gravitational waves from the coalescence of two compact objects. We cover a broad range of the parameter space and we search for gravitational waves in the second and third observation runs. The results are compared with the official catalog events.

Date of Award	19 Dec 2022
Original language	English
Supervisor	Mario Martinez Pérez (Director)