From the Big Bang to Tumbleweeds: Analysis of Signals from Relic Gravitons, Neutron Stars, and Terrestrial Gravitational Noise in Gravitational Wave Detectors

Citation

Creighton, Teviet David (2000) From the Big Bang to Tumbleweeds: Analysis of Signals from Relic Gravitons, Neutron Stars, and Terrestrial Gravitational Noise in Gravitational Wave Detectors. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6xcj-0z64. https://resolver.caltech.edu/CaltechTHESIS:08302017-093459499

Abstract

This dissertation explores three separate issues in the field of gravitational-wave astronomy: optimal detection algorithms for quasi-periodic signals, gravitational-wave signatures of the equation of state in the early universe, and local Newtonian gravitational noise from nearby airborne masses as possible contaminants of the gravitational-wave signal.

Continuous quasi-periodic signals are waveforms that maintain phase coherence over times longer than practical observation times, although the phase may drift in a way that can be modeled with few parameters. Sensitivity to such signals is limited by the computational cost of the analysis, especially since the detection algorithm must search over many values of the parameters in the phase model; it is therefore crucial to develop computationally efficient search strategies. One such strategy is a hierarchical stack search: a technique combining coherent phase corrections on short stretches of data with incoherent frequency drift corrections among several such stretches. The procedure is repeated at least twice, with each pass increasing the confidence in any putative signal. This dissertation discusses how to choose parameter values and observation times for greatest sensitivity, and shows how several astrophysically interesting sources may be detectable by this method.

A background of gravitational waves originating in the Big Bang or a pre-Big-Bang collapsing universe will not thermalize in any cosmological epoch, but may be amplified by an intermediate epoch when the wavelengths were stretched outside the Hubble radius. The present-day spectral index is related simply and generically to the initial spectrum, and to the cosmological equation of state at the beginning and end of the intermediate epoch. This dissertation derives this relation, and compares it to related but more model-specific formulae in the current literature.

Finally, this dissertation considers two atmospheric sources of background Newtonian gravita­tional noise (infrasonic pressure waves and wind-advected density perturbations), and two sources of transient Newtonian gravitational signals (atmospheric shockwaves and massive airborne bodies, especially tumbleweeds). Neither background noise source will exceed the noise floor for advanced detectors, but sonic booms and wind-borne debris striking the detector can both produce detectable spurious signals through their gravitational effects. Possible corrective measures arc discussed.

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