| Incoherent superposition of gravitational waves from a large number of unresolved sources gives rise to the stochastic gravitational-wave background. This background could be of cosmological origin, produced by early universe events such as inflation. It could also be of astrophysical origin, produced by a large number of astrophysical objects such as binary neutron stars and black holes. Detection of the stochastic gravitational wave background would therefore provide information both about the state of the universe at its earliest moments and about its evolution at later times. Long gravitational-wave transients are gravitational waves whose times scales range from minutes to weeks. Such long gravitational-wave transients are predicted by a variety of astrophysical models, including stellar core collapse and accretion onto newly formed proto-neutron stars and black holes. Detection of long transient gravitational waves would provide clues about various dynamical process occurring in these astrophysical objects. In this thesis, we describe methods to search for stochastic and long transient gravitational waves in interferometric gravitational-wave detector data and present results obtained by using the Laser Interferometer Gravitational-wave Observatory (LIGO) data acquired during its fifth science run. |
