The first direct detection of gravitational waves opened the possibility of mapping the Universe via this new and independent messenger. Indeed, during their propagation, gravitational waves pick... Show moreThe first direct detection of gravitational waves opened the possibility of mapping the Universe via this new and independent messenger. Indeed, during their propagation, gravitational waves pick up information about the spacetime as they are affected by its expansion and by the matter structures along the propagation path. The aim of this Thesis is to investigate which cosmological information is accessible from a gravitational wave detection, with a specific interest in the late time Universe. Show less
At the largest scales, two ingredients dictate the distribution of matter in the Universe. The first is dark matter, acting as an invisible scaffolding held together by gravitational forces. The... Show moreAt the largest scales, two ingredients dictate the distribution of matter in the Universe. The first is dark matter, acting as an invisible scaffolding held together by gravitational forces. The second is dark energy, an enigmatic component responsible for the accelerated expansion of the Universe. Under these two forces, matter in the Universe organizes itself in the so-called cosmic web. The nodes of this network are large dark matter haloes, and this thesis explores how their boundaries provide information about the nature of dark energy and cosmology. Chapters 3 and 4 present robust theoretical predictions for this titular edge and discuss its simple physical interpretation. Chapters 2 and 5 corroborate these results by presenting measurements of this feature in weak-lensing data. The last scientific chapter of this thesis is a collection of studies in gravitational-wave physics. This chapter explores how these spacetime ripples observed from across the cosmos can be used to detect alternative theories of gravity. Show less
In this paper, which is of programmatic rather than quantitative nature, we aim to further delineate and sharpen the future potential of the LISA mission in the area of fundamental physics. Given... Show moreIn this paper, which is of programmatic rather than quantitative nature, we aim to further delineate and sharpen the future potential of the LISA mission in the area of fundamental physics. Given the very broad range of topics that might be relevant to LISA,we present here a sample of what we view as particularly promising fundamental physics directions. We organize these directions through a "science-first" approach that allows us to classify how LISA data can inform theoretical physics in a variety of areas. For each of these theoretical physics classes, we identify the sources that are currently expected to provide the principal contribution to our knowledge, and the areas that need further development. The classification presented here should not be thought of as cast in stone, but rather as a fluid framework that is amenable to change with the flow of new insights in theoretical physics. Show less
For centuries astronomers studied the Universe by collecting light. Nowadays, we are living in times of great technological advancements, which allow us to explore our Universe in a new way -... Show moreFor centuries astronomers studied the Universe by collecting light. Nowadays, we are living in times of great technological advancements, which allow us to explore our Universe in a new way - though gravitational wave radiation. There are many gravitational wave sources in our own Galaxy, the Milky Way. For example, white dwarf stars in tight binary systems spinning around each other in less than 1 hour. LISA is a future ESA mission, that will detect a large variety of gravitational wave sources including Galactic double white dwarfs. Although quite faint, double white dwarfs can also be seen by optical telescopes. Thus, astronomers call them “multi-messenger” sources. This means that we can collect information from them using more than one messenger: electromagnetic waves, messengers of the electromagnetic field, and gravitational waves, messengers of the gravitational field. This thesis proposes to use gravitational wave signals from Galactic double white dwarfs to study the Milky Way and its neighbourhood. In particular, it explores how by collecting many electromagnetic and gravitational wave signals from thousands to millions of binary double white dwarfs spread all across our Galaxy, we can perform multi-messenger Galactic Astronomy and learn about the structure and history of the Milky Way. Show less
Long-term precise timing of Galactic millisecond pulsars holds great promise for measuring long-period (months-to-years) astrophysical gravitational waves. In this work we develop a Bayesian data... Show moreLong-term precise timing of Galactic millisecond pulsars holds great promise for measuring long-period (months-to-years) astrophysical gravitational waves. In this work we develop a Bayesian data analysis method for projects called pulsar timing arrays; projects aimed to detect these gravitational waves by using millisecond pulsars as very precise extraterrestrial clocks. We also introduce the gravitational-wave memory effect, and we describe how to detect this effect with pulsar timing arrays with the Bayesian method. The Bayesian data analysis method is developed, extensively tested, and applied to real data. This has resulted in the most accurate upper-limit on the stochastic gravitational-wave background. Show less
