Topics in Gravitational-Wave Physics

Citation

Savov, Pavlin (2008) Topics in Gravitational-Wave Physics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/72z7-n083. https://resolver.caltech.edu/CaltechTHESIS:07152021-205059459

Abstract

While the astrophysics community is on the brink of detecting the first gravitational-wave signal [1, 2, 3], efforts continue to improve the existing detectors and develop new technologies for future-generation detectors. In parallel, the need is rapidly growing for improved analyzes and interpretations of the science data that comes from the detectors. This thesis contributes to these issues with research results related to (i) the design of possible upgrades for the Advanced detectors for the ground-based Laser Interferometer Gravitational-wave Observatory (AdvLIGO) [4, 5, 6, 7] (i.e. for improved versions of the initial LIGO detectors [9, 10]), and (ii) future data analysis techniques for the Laser Interferometer Space Antenna (LISA) [11, 12] (a planned space-based gravitational-wave mission). More specifically:

Currently, an international array of first-generation ground-based, laser-interferometer gravitational-wave detectors (consisting of LIGO, VIRGO [13, 14], GEO600 [15, 16] and TAMA300 [17]) is actively searching for gravitational waves in the frequency band (10 Hz { 10 kHz), with peak sensitivity at a few hundred Hertz. On September the 30th, 2007, the initial LIGO interferometers finished their Science Run 5 (S5) [18], which collected one year of triple coincidence data at the interferometers' design sensitivity. The next version of LIGO's interferometers, called Enhanced LIGO [19], with amplitude sensitivity improved by a factor about 2 (event rate increased by a factor 2³≃10), is being implemented and will collect data in science mode in 2009-10. Advanced LIGO is expected to begin operations around 2013. At the end of commissioning, it will have a factor ten better amplitude sensitivity than initial LIGO, which translates to a thousand-fold increase in event rate. Therefore, just a few hours of observations by AdvLIGO will be worth the entire lifetime of initial LIGO. Another significant advantage of the Advanced LIGO design is that it will allow tuning of the sensitivity as a function of frequency, so as to optimize searches for specific astrophysical sources with specific expected spectra.

LISA, the first system of space-based gravitational-wave interferometers, is planned for launch and science operation in 2018 or perhaps somewhat later, depending on political developments. It will operate with peak sensitivity around a few milliHertz and should detect galore of signals simultaneously. The lifetime of the mission is expected to be around five years.

This thesis consists of four chapters: this introductory chapter, two chapters (2 and 3) dealing with research relevant to the technology for a possible upgrade of Advanced LIGO, and one chapter (4) relevant to data analysis for LISA. Specifically: Chapter 2 elucidates the influence of the shape (power profile) of an interferometer's arm-cavity light beams on a tilt instability, in which the tilt of an arm cavity mirror is driven by light pressure. Chapter 3 proves a duality relation between arm cavities with almost at mirrors (as originally planned for AdvLIGO) and cavities with almost concentric spherical mirrors (a design change that has been made, to control the tilt instability). I discovered and used this duality relation numerically in the research reported in Chapter 2, but only later, in collaboration with others, did I prove the duality relation analytically (Chapter 3). Chapter 4 reports details of and results from a Mock LISA Data Challenge in which gravitational wave signals from (mock) supermassive black-hole binaries were sought and found in simulated LISA data.

Thesis Files