Doutorado em Astrofísica, Cosmologia e Gravitação
URI Permanente para esta coleção
Nível: Doutorado
Ano de início: 2016
Conceito atual na CAPES: 5
Ato normativo: Parecer 487/2018
Periodicidade de seleção: Semestral
Área(s) de concentração: Astronomia e Física
Url do curso: https://cosmologia.ufes.br/pt-br/pos-graduacao/PPGCosmo/detalhes-do-curso?id=1453
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Submissões Recentes
- ItemWeak gravitational lensing in interacting dark sector models(Universidade Federal do Espírito Santo, 2025-08-22) Capel Sica, Paola Terezinha Zanolla Seidel e; Silva, Saulo Carneiro de Souza; https://orcid.org/0000-0001-7098-383X; http://lattes.cnpq.br/; Benetti, Micol; https://orcid.org/0000-0002-3670-7214; http://lattes.cnpq.br/3234425698221975; Fabris, Júlio César; https://orcid.org/0000-0001-8880-107X; http://lattes.cnpq.br/5193649615872035; https://orcid.org/0000-0002-5403-8923; http://lattes.cnpq.br/; Alcaniz, Jailson Souza de; https://orcid.org/0000-0003-2441-1413; http://lattes.cnpq.br/4351190607357917; Velten, Hermano Endlich Schneider; https://orcid.org/0000-0002-5155-7998; http://lattes.cnpq.br/0282590467459210; von Marttens, Rodrigo Fernando Lugon Cornejo; https://orcid.org/0000-0003-3954-5756; http://lattes.cnpq.br/7980376506204515; Marques, Gabriela Antunes; https://orcid.org/0000-0002-8571-8876; http://lattes.cnpq.br/0675863411047105We explore the lines that underpin the knowledge of weak gravitational lensing, study ing basic cosmological concepts, and the construction of the matter power spectrum for ΛCDM and different scenarios. Our main goal is to investigate the possibility of interaction in the dark sector through a set of models that employ the weak lens ing formalism. This strategy proves to be promising, as the three-dimensional matter power spectrum can be directly probed with this tool. Another objective is to update the constraints on relevant cosmological parameters, including the interaction param eter of the proposed model. The spacetime is assumed to be flat and described by the Friedmann–Lemaˆıtre–Robertson–Walker metric, applied to a non-adiabatic decom posed generalized Chaplygin gas. In this framework, we recover the behavior of cold dark matter at high redshifts and of a cosmological constant in the asymptotic limit. Numerical testing is therefore crucial to evaluate the models. For this purpose, we use the CLASS Boltzmann code to simulate the interaction model, and the Cobaya sampler to compare different models, particularly with cosmic shear data from the first year of the DES-Y1 survey and with CMB data. We know that early and late-time observables do not agree with the theme of dark sector dynamics, and in this context, our investigation may contribute to assessing whether a systematic discrepancy exists between these measurements. In general, our results are consistent with the CMB data, except for the Hubble constant, H0. Our best-fit value for this parameter was lower than the standard CMB value. We find that, in the context of this dark sector study, the interaction is strongly constrained and the ΛCDM model is favored.
- ItemAstrophysical tests of strong-field gravity: pulse profile modeling and boundary conditions in neutron stars(Universidade Federal do Espírito Santo, 2025-03-14) Costa, Tulio Ottoni Ferreira da; Rueda Hernández, Jorge Armando; https://orcid.org/0000-0003-4904-0014; http://lattes.cnpq.br/2748521487712356; Coelho, Jaziel Goulart; https://orcid.org/0000-0001-9386-1042; http://lattes.cnpq.br/0298932683600051; https://orcid.org/0000-0003-3785-4918; http://lattes.cnpq.br/0721147143986351; Araújo, José Carlos Neves de; https://orcid.org/0000-0003-4418-4289; http://lattes.cnpq.br/6217296674061205; Arbañil, José; https://orcid.org/0000-0002-2623-4900; http://lattes.cnpq.br/2580853999834669; Velten, Hermano Endlich Schneider; https://orcid.org/0000-0002-5155-7998; http://lattes.cnpq.br/0282590467459210We live in a golden age to explore gravity in the strong field regime of compact objects. Present and future multimessenger experiments will allow precision tests with high-energy electromagnetic radiation and gravitational waves, probing the relativistic environment of compact objects. This thesis comprises two main parts and explores the strong gravity of neutron stars (NS). In the first part, we compute bolometric light curves from emitting hot spots on the surface of pulsars in the context of the Scalar-Tensor theory of gravity. This calculation considers several relativistic ingredients that affect the observed flux, such as Doppler shift, light bending, and time delay. We show that highly compact NSs, with compactness close to GM/Rc2 ∼ 0.284, are ideal astrophysical laboratories to seek deviations of General Relativity (GR) because of the light curve’s sensitivity to the gravity theory. In the second part, we explore the possibility of non-rigid rotation of NSs, studying a toy model that captures the main idea of a stratified rotation. We show the impact of different parts of the NS rotating with different angular velocities on the moment of inertia, exploring some of its astrophysical consequences. Our study aims to call attention to possible systematics when performing inference of NS parameters by techniques such as the timing of radio pulses or pulse profile modeling when assuming that the star rotates rigidly.
- ItemOn the degenerate dynamics of branched hamiltonians(Universidade Federal do Espírito Santo, 2024-09-21) Ferreira Junior, Alexsandre Leite; Zanelli, Jorge; https://orcid.org/0000-0001-7512-4284; Pinto-Neto, Nelson; https://orcid.org/0000-0001-6713-5290; Fabris, Júlio; Piattella, Oliver Fabio; Bittencourt, Eduardo; Gannouji, Radouane; Helayël-Neto, JoséBranched Hamiltonians and the corresponding singularity are present in several inter esting physical systems: Lovelock extension of General Relativity in higher dimensions, classical time crystals, k-essence fields, Horndeski theories, compressible fluids, and nonlinear electrodynamics. The emergent ill defined sympletic structure and tricky dynamical evolution poses challenges to a consistent interpretation. In this thesis, multi-valued Hamiltonians are investigated in the framework of degenerate dynamical system, whose sympletic form does not have a constant rank, allowing novel features and interpretations not present in previous investigations. In particular, it is shown how the multi-valuedness is associated with a dynamical mechanism of dimensional reduction, as some degrees of freedom turn into gauge symmetries when the system degenerates. In the case of classical time crystal, there is no “moving” ground state nor brick wall solution, as described previously. Moreover, the degenerate dynamics of a k–essence model enables it to be responsible for both primordial inflation and the present observed acceleration of the cosmological background geometry, while also admitting a non-singular de Sitter beginning of the Universe (it arises from de Sitter and ends in de Sitter). Furthermore, the model is free of pathologies such as propagating superluminal perturbations, negative energies, and perturbation instabilities. Henceforth, in thesis is demonstrated that the degenerate dynamics offer a consistent interpretation, under which the degeneracy and consequent branching is not a problem but a dynamical feature.
- ItemThe redshift drift as a new cosmological probe(Universidade Federal do Espírito Santo, 2024-09-19) Dutra, Pedro Henrique Bessa Rodrigues; Durrer, Ruth; https://orcid.org/0000-0001-9833-2086; Marra, Valerio; https://orcid.org/0000-0002-7773-1579; Marttens, Rodrigo vom; Piattella, Oliver Fabio; Koksbang, Sofie Marie; Martins, CarlosWith the advent of precision cosmology and the next generation of telescopes and sur veys, observations will allow the standard cosmological model to be tested in old and new regimes with unprecedented accuracy, and the data will demand accurate the oretical models of cosmological phenomena in order to be properly interpreted and processed. Theorists are reassessing old and new probes that allow the current cosmo logical paradigm to be tested to its limits. One promising new probe, the measurement which is one of the main objectives of the ELT ANDES spectrograph, is the cosmic redshift drift. One of the theoretical predictions of cosmological models based on Robertson-Walker metrics is the cosmic redshift drift, which measures the real-time rate of change of the spectra of far away sources, and is a generic consequence of cosmological models where the expansion rate is non-constant. Its observation provides a model independent way to measure the time variation of the Universe’s expansion and as such, an independent test of the late-time acceleration phase of the Universe and the existence of a cosmo logical constant. In this thesis we study the redshift drift in realistic cosmological models containing inhomogeneities in the !CDM paradigm. We derive for the first time a gauge-invariant expression for the redshift drift and its power spectrum, and implement the redshift drift f luctuation power spectrum numerically through Einstein-Boltzmann codes and using n-body simulations, providing a solid theoretical foundation for future measurements and observations of the redshift drift in !CDM cosmology and beyond.
- ItemProbing cosmology with an eye on Rubin : from strong lensing to the large scale structure of the universe(Universidade Federal do Espírito Santo, 2024-04-11) Oliveira, Renan Alves de; Ho, Shirley ; https://orcid.org/0000-0002-1068-160X; Makler, Martín; https://orcid.org/0000-0003-2206-2651; http://lattes.cnpq.br/6567844719949395; https://orcid.org/0000-0002-0200-3833; http://lattes.cnpq.br/1895596998416086; Abramo, Luis Raul Weber ; https://orcid.org/0000-0001-8295-7022; http://lattes.cnpq.br/4558796258762790; Bom, Clécio Roque de ; https://orcid.org/0000-0003-4383-2969; http://lattes.cnpq.br/5635352837026339; Velten, Hermano Endlich Schneider ; https://orcid.org/0000-0002-5155-7998; http://lattes.cnpq.br/0282590467459210; Marra, Valerio ; http://orcid.org/0000-0002-7773-1579; http://lattes.cnpq.br/6846011112691877In 2024, the Vera C. Rubin Observatory will begin observing the Universe for the next ten years. Two key cosmological observables that Rubin will probe are gravitational lensing and the large-scale structure of the Universe. In this thesis, we derive analytical solutions for strongly lensed images that can be useful for generating fast simulations and as a starting point in parameter searches for lens inversion. Then, we obtain an expression in closed form for the magnification cross-section, which can be used to predict the abundance of highly magnified sources. Next, we focus on real data and assemble an extensive compilation of Strong Lensing candidate systems from the literature containing over 30,000 unique objects. We cross-match this sample with the current major photometric and spectroscopic catalogs. As preparation for Rubin, we generate image cutouts for these systems in most current wide-field surveys with subarcsecond seeing, namely DES, HSC, KiDS, CFHTLens, RCSLens, and CS82. This sample dubbed the “Last Stand Before Rubin” (LaStBeRu), has a myriad of applications, from using archival data to selections for follow-up projects and training of machine learning algorithms. As an application, we have performed a test of General Relativity (GR) with these data, combining information from strong lensing and velocity dispersions, which allow one to set constraints on the Post-Newtonian parameter γPPN. From the LaStBeRu database, we were able to provide the first independent test of γPPN from previous results and for the first time only for systems identifiable in ground-based images. We can obtain the most stringent constraint on γPPN by combining these data with the current samples. Moreover, we have obtained new spectroscopic data for systems selected from LaStBeRu, which were used to obtain the first end-to-end determination of γPPN. It is also the first determination derived purely from ground-based data and the first to use self-consistent priors. Our results are consistent with GR at the ∼ 1-σ level and with the previous results from the literature. Finally, in the context of the large structure, we present two neural emulators capable of making fast predictions for the density, displacement, and velocity fields of dark matter particles without necessarily having to run expensive N-body simulations. We compared these emulators with another fast method for the same task, showing that neural emulators provide the best results