Forecasted experimental sensitivities to the cosmic microwave and stochastic gravitational wave backgrounds
File(s)
Author(s)
Gleave, Eleanor
Type
Thesis
Abstract
Gravitational wave (GW) observations probe a diffuse, stochastic gravitational wave back-
ground (SGWB) in addition to individual cataclysmic events, such as the mergers of two
compact objects. The detection and description of the SGWB requires somewhat different
techniques to those required for individual events, for both direct and indirect observations.
In this thesis, I first probe the sensitivity of present and future GW experiments to different
background sources, including those expected from unresolved compact binaries in their quasi-
Newtonian inspiral and eventual mergers, as well as more speculative cosmological sources such
as inflation, cosmic strings, and first-order phase transitions, over frequencies ranges where
those sources can be described by a single power law. I develop a Fisher matrix formalism to
forecast the upcoming sensitivities of individual, and (combinations of) multiple experiments,
and novel visualisations taking into account the increase in sensitivity to the SGWB with time.
I subsequently develop this methodology to probe the sensitivities of these experiments to
deviations from a single power law, aiming to ultimately evaluate sensitivities to more complicated spectral shapes (which are a more accurate fit to cosmological spectra).
Then, I present the work I have done for the Simons Observatory (SO), a cosmic microwave
background (CMB) experiment currently in initial science observations (ISO). Precise measurements of the CMB are a method for indirect observations of the SGWB—measuring the
primordial GWB (through effects on the CMB temperature and polarisation power spectra)
constrains the overall SGWB.
I present the two campaigns of work I carried out, on the optimisation of the scanning
strategies for the Large and Small Aperture Telescopes, presenting new baseline strategies for
each. These strategies are being tested during ISO. There is particular discussion of the
implications of the proposed scanning strategies for the sensitivity of SO to the primordial
GWB.
ground (SGWB) in addition to individual cataclysmic events, such as the mergers of two
compact objects. The detection and description of the SGWB requires somewhat different
techniques to those required for individual events, for both direct and indirect observations.
In this thesis, I first probe the sensitivity of present and future GW experiments to different
background sources, including those expected from unresolved compact binaries in their quasi-
Newtonian inspiral and eventual mergers, as well as more speculative cosmological sources such
as inflation, cosmic strings, and first-order phase transitions, over frequencies ranges where
those sources can be described by a single power law. I develop a Fisher matrix formalism to
forecast the upcoming sensitivities of individual, and (combinations of) multiple experiments,
and novel visualisations taking into account the increase in sensitivity to the SGWB with time.
I subsequently develop this methodology to probe the sensitivities of these experiments to
deviations from a single power law, aiming to ultimately evaluate sensitivities to more complicated spectral shapes (which are a more accurate fit to cosmological spectra).
Then, I present the work I have done for the Simons Observatory (SO), a cosmic microwave
background (CMB) experiment currently in initial science observations (ISO). Precise measurements of the CMB are a method for indirect observations of the SGWB—measuring the
primordial GWB (through effects on the CMB temperature and polarisation power spectra)
constrains the overall SGWB.
I present the two campaigns of work I carried out, on the optimisation of the scanning
strategies for the Large and Small Aperture Telescopes, presenting new baseline strategies for
each. These strategies are being tested during ISO. There is particular discussion of the
implications of the proposed scanning strategies for the sensitivity of SO to the primordial
GWB.
Version
Open Access
Date Issued
2025-06-13
Date Awarded
01/12/2025
License URL
Advisor
Jaffe, Andrew
Sponsor
Science and Technology Facilities Council (Great Britain)
Publisher Department
Department of Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)