The gravitational wave background: observational prospects with the next generation experiments
File(s)
Author(s)
Mentasti, Giorgio
Type
Thesis
Abstract
Over the past decade, gravitational-wave (GW) astronomy has transitioned from a theoretical frontier to a precision observational science, offering unprecedented insights into the most energetic phenomena in the universe. This thesis advances the study of the stochastic gravitational-wave background (SGWB)—the diffuse superposition of unresolved GW sources—across a broad frequency spectrum, spanning ground-based interferometers, space-based detectors, pulsar timing arrays (PTAs), and astrometric observatories.
We develop a unified formalism to model anisotropies and polarization in the SGWB, applicable to current and next-generation interferometric networks, such as the Einstein Telescope, Cosmic Explorer, LISA, and Taiji. This framework enables, for the first time, a systematic evaluation of the limits imposed by instrumental noise and cosmic variance on the measurement of anisotropies and polarization of the GW background.
The thesis further extends the formalism to non-interferometric probes of low-frequency GWs. We introduce a general framework to describe observables for nanohertz GWs surveys. We propose a novel astrometric technique to probe time-dependent shape distortions in resolved astrophysical sources induced by gravitational waves and short-distance astrometry. The predicted two-point correlation functions for this astrometric shear effect mirror the Hellings–Downs signature from PTAs and open a novel observational window using upcoming surveys such as Gaia and the Vera C. Rubin Observatory’s LSST.
By integrating comprehensive modeling of GW observables, response functions and innovative detection strategies, this work provides a general framework on the mathematical and statistical tools that will be crucial in the next era of GW science. Its findings support the science case and analysis pipelines of current and future GW observatories, with implications for astrophysics, cosmology, and the physics of the early universe.
We develop a unified formalism to model anisotropies and polarization in the SGWB, applicable to current and next-generation interferometric networks, such as the Einstein Telescope, Cosmic Explorer, LISA, and Taiji. This framework enables, for the first time, a systematic evaluation of the limits imposed by instrumental noise and cosmic variance on the measurement of anisotropies and polarization of the GW background.
The thesis further extends the formalism to non-interferometric probes of low-frequency GWs. We introduce a general framework to describe observables for nanohertz GWs surveys. We propose a novel astrometric technique to probe time-dependent shape distortions in resolved astrophysical sources induced by gravitational waves and short-distance astrometry. The predicted two-point correlation functions for this astrometric shear effect mirror the Hellings–Downs signature from PTAs and open a novel observational window using upcoming surveys such as Gaia and the Vera C. Rubin Observatory’s LSST.
By integrating comprehensive modeling of GW observables, response functions and innovative detection strategies, this work provides a general framework on the mathematical and statistical tools that will be crucial in the next era of GW science. Its findings support the science case and analysis pipelines of current and future GW observatories, with implications for astrophysics, cosmology, and the physics of the early universe.
Version
Open Access
Date Issued
2025-08-19
Date Awarded
01/10/2025
License URL
Advisor
Contaldi, Carlo
Publisher Department
Department of Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)