A search for gravitational waves signals emitted by binary black holes systems with precessing spins

During the inspiral of two merging black holes, if the spin of one or of both bodies are misaligned with respect to the orbital angular momentum ˆ L, the total spin ˆ S and ˆ L will have a precessing motion around the direction of the total angular momentum ˆ J of the system. The orbital plane of the system will also precess over time due to the general relativistic spin-spin and spin-orbit interactions. The imprinting of the precession will appears as phase and amplitude modulations in the observed signal, thus precessing gravitational waves (GW) will have a more rich structure than the charasteristic chirp-shape of the aligned-spin ones. These precession-induced modulations will be important not only for waves from Binary Black Holes (BBH) which lie in the current LIGO-Virgo frequency band sensitivity, but also for waves emitted by supermassive BBH and for binary neutron stars mergers or stellar mass BH spiraling into supermassive BHs (these low frequency GW will be the target signals for space based GW detectors like LISA). Imprints of precession have been investigated in several signals of the current' 90 BBH detections of Advanced LIGO and Virgo detectors, and therearealmosttwosignalswithevidenceofmarginalprecession: GW190412[13]and GW200129 [14]. In addition, the observation of GW signals with precession not only have the goal to test General Relativity in strong field regime and to study binary formation channels using spin-distribution population [87], [89], but the most promising challenge is to improve the performance of early warning alerts for electromagnetic follow-up of the GW sources [90]. In this research work a search for GW signals emitted by BBH with precession of the spins is proposed. The thesis is divided in five chapters organized as follow: the first chapter is dedicated to an introduction of GWs, who’s existence is predicted by the theory of General Relativity. After showing that they are solutions of Einsten’s linearizedfieldequationsandtheirquadrupolenature,thesystem(transverse-tracelessgauge) used to describe the interaction between a GW and a detector is illustrated. Also, the main astrophysical sources of GWs are described; In the second chapter GW detectors and the interferometric technique are described. In addition, several noise sources at different frequency ranges which affect the detectors output data are illustrated. In the thirdchapterthetheoryofprecessionofspinsinBBHsystemsisintroduced. Inparticular, the simple precession motion, which occurs when the direction of the binary’s total angular momentum is approximatly constant in time, will be analized and the equations to describe the orbital plane of the system and the spin-induced modulations in the gravitational signature will be derived. The fourth and the fifth chapters contain the main contribution of this work. In the fourth chapter the tools Sbank and Banksim of the pipeline PyCBC are described, used for the generation of the precessing-spin and aligned-spin template banks and the computation of their effectualness respectively. In the fifth chapter, first an outline of the pipeline MBTA based on the matched-filtering technique is depicted; then the results of Monte Carlo tests, performed running MBTA to analize the capability of the template banks to recover simulated signals of GW with precession of the spins in Gaussian noise and in a file of O3 data, are discussed.