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
The ultimate goal of cosmologists is to find a cosmological model able to explain the current observational data. In this sense, the Standard Cosmological model establishes that our universe is... Show moreThe ultimate goal of cosmologists is to find a cosmological model able to explain the current observational data. In this sense, the Standard Cosmological model establishes that our universe is mainly composed of two unknown components: a type of matter that is known to only interact through gravitation, Cold Dark Matter, and a substance responsible for the current accelerated expansion of the universe that can be modelled by a cosmological constant. Still, this model, though successful, fails to answer hot-burning questions in the field. For this reason, theoretical cosmologists focus on developing further modifications of the model to test them against astrophysical data and check whether alternative scenarios can provide a better explanation of the observations.This thesis is dedicated to the Bayesian statistical analyses of extensions of the Standard Cosmological model using several astronomical data sets, and to the forecast of new observables and experiments. The first part focuses on data science and inflation, and it aims to constrain inflationary models using advanced inference techniques. The second part of the thesis is dedicated to the novel concept of cross-correlations of gravitational-wave physics and large scale structure observables. The third part of this thesis is dedicated to the incoming ESA Euclid satellite, and in particular, it focuses on a crucial data science analysis software for the mission: the code “Cosmological Likelihood for Observables in Euclid”, also known as CLOE. Show less
Three major cosmology-focused missions are planned for the next decade: the Euclid space telescope, the Vera C. Rubin Observatory in Chile, and the Nancy Grace Roman Space Telescope. Their surveys... Show moreThree major cosmology-focused missions are planned for the next decade: the Euclid space telescope, the Vera C. Rubin Observatory in Chile, and the Nancy Grace Roman Space Telescope. Their surveys will detect billions of galaxies over more than a third of the celestial sphere and out to redshifts of z~2 to constrain the evolving matterdistribution using weak gravitational lensing. This thesis focusses on ways of disentangling the contribution of normal matter, baryons for cosmologists, from the measured weak lensing signal for cosmic shear analyses and galaxy cluster mass calibrations. Combining the predictions of computer-simulated universes, evolving billions of particles in time, with simplified models that reproduce the observeddistribution of hot gas inside clusters of galaxies, but that freely vary the amount of matter where no observations are available, we have quantified how strongly our ignorance of the relation between ordinary and dark matter will affect the analysis of the planned surveys. Additionally, we have studied how baryons affect cluster massdeterminations and we suggest a new analysis method for cluster abundance studies that is less sensitive to our lack of knowledge of the exact distribution of normal matter in the outskirts of galaxy clusters. 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 astronomy, the interpration of observations and measurements plays a crucial role: we rely purely and fundamentally on the information that reaches us as observers. And 80% of all matter in the... Show moreIn astronomy, the interpration of observations and measurements plays a crucial role: we rely purely and fundamentally on the information that reaches us as observers. And 80% of all matter in the universe is undetectable directly.This so called 'dark matter' can be observed indirectly, by the gravitational effect on its surroundings and the curvature of spacetime predicted by the theory of relativity.In this thesis, we combine scientific research, a description of our universe, with theoretical considerations of the statistical methods used for that research, or how we can deduce that description from the 'reflections' that we see. In this work, we focus on the matter distribution in groups and clusters of galaxies, and consider the intricacies of the method of weak gravitational lensing that we use, respectively. Show less
Galaxies form and live inside dark matter haloes. As a consequence, they are exposed to the tidal fields generated by the surrounding matter distribution: this imprints a preferential direction to... Show moreGalaxies form and live inside dark matter haloes. As a consequence, they are exposed to the tidal fields generated by the surrounding matter distribution: this imprints a preferential direction to the galaxy shapes, which leads to a coherent alignment on physically close galaxies, called intrinsic alignment. Intrinsic alignment is an important contaminant to weak lensing, which instead uses the correlation of galaxy shapes caused by the lensing effect of the matter distribution along the line of sight to infer the amount and the distribution of matter in the Universe.This dissertation studies the dependence of intrinsic alignment on galaxy properties such as luminosity, redshift and halo mass, using different techniques to measure it. It presents a model to account for the scale and sample dependence of the intrinsic alignment signal when modelling it in weak lensing studies. It also investigates the amount of biasing that incorrect modelling of intrinsic alignment would induce in the inferred cosmological parameters for ongoing and future surveys. The potential of weak lensing magnification is also explored to help constrain the cosmological parameters in upcoming surveys. Show less
This thesis is dedicated to the exploration of the primordial dark ages: unknown physics during the earliest stages of the Universe’s expansion that have not yet been directly probed by... Show moreThis thesis is dedicated to the exploration of the primordial dark ages: unknown physics during the earliest stages of the Universe’s expansion that have not yet been directly probed by observations. Cosmic inflation is a burst of exponential expansion of space after the “Big Bang”. The energy that drives inflation must be transferred to elementary particles and radiation. This process is called reheating. The unknown expansion history of the universe during the reheating era connects the cosmic microwave background (CMB) observations to inflationary physics. CMB is a relic radiation that provides us a snapshot of the primordial universe. Both the inflationary and reheating eras generate signatures to be seen via upcoming gravitational waves and CMB polarization experiments. In this thesis we show analytically a scaling behaviour that allows for an easy estimate of the reheating efficiency for one broad family of multi-field models of inflation that is called α-attractors. We show the influence of the asymmetry around the minimum of potential on the reheating efficiency. Moreover, we study the predictions for chiral gravitational waves production by a spectator gauge field sector in scalar single-field inflation. Finally, we present a new class of inflationary models that is called “shift-symmetric orbital inflation”. Show less
The civilizations of ancient China and Mesoamerica, although not historically related and obviously different in many specific aspects (such as language and writing), show many interesting... Show moreThe civilizations of ancient China and Mesoamerica, although not historically related and obviously different in many specific aspects (such as language and writing), show many interesting commonalities and similar tendencies in their cultural manifestations. The aim of this thesis is to examine the validity of contemporary cosmological interpretations of architecture and related visual art in both regions.In comparing the cosmological characteristics and the performance in the architecture of ancient China and Mesoamerica this thesis has a multidisciplinary focus (considering architecture, archeology, astronomy, history and anthropology). Through comparison, it is found that the two have many similarities in their cosmological theory: they have similar azimuth characteristics (associated with colors, directional gods, seasons, life and death, etc.), their buildings are rich in space orientation; they both have Three Realms (Heaven, Earth, Underworld) and a similar life and death concept, especially they all worship their ancestors; furthermore, they use a similar Calendar Round in their respective calendars. In the performance of architecture, they use their own methods to integrate the concept of cosmology into architectural creation, which makes their architecture establish connections among the cosmos, gods, and time. Show less
Davies, C.T.; Paillas, E.; Cautun, M.; Li, B. 2021
