Orientador: Pedro Cunha de Holanda / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-14T09:35:59Z (GMT). No. of bitstreams: 1 Motta_MarieleKatherineFaria_M.pdf: 2935959 bytes, checksum: 36090b361909fca742a96d1606e1904d (MD5) Previous issue date: 2009 / Resumo: A formação das estruturas ao longo da história do universo depende crucialmente da competição entre efeitos de matéria não-relativística e relativística. Sabemos que existem mecanismos que convertem os conteúdos de uma em outra. Em particular, a explosão de uma supernova tipo colapso do núcleo converte uma energia correspondente a 99% da energia de ligação da estrela de nêutrons remanescente em neutrinos relativísticos. Nos baseamos neste processo para construir um modelo de conversão de matéria escura em matéria relativisstica que evolui com a história do universo e avaliamos os efeitos dessa conversao sobre a formação de estruturas em grandes escalas / Abstract: The structure formation through the history of the universe crucially depends on the competition between non-relativistic and relativistic matter effects. We know that there are mechanisms which convert the contents of one into the other. Particularly the explosion of a core-collapse supernova converts an energy corresponding to 99% of the gravitational binding energy of the remnant neutron star into relativistic neutrinos. Based on this process we have built a conversion model of dark matter into relativistic matter that evolves throughout the history of the universe and we evaluate the effects of this conversion over the large scale structure formation / Mestrado / Física / Mestra em Física

The advent of laser cooling and optical manipulation for atomic samples revolutionized atomic physics in 1990’s, allowing the creation of new phases of matter, more accurate atomic clocks, and enabling leading candidates for the first functional quantum computer. This could not have been predicted at the time, and is a testament to the value of fundamental research for its own sake. These same laser cooling techniques are now being applied to simple molecular systems with the same revolutionary potential. In this thesis, I will present a range of experiments exploring these schemes in a new class of molecules, the diatomic alkaline earth hydrides. We present the creation and characterization of a bright beam of cold barium hydride molecules, high precision spectroscopy of these samples, as well as optical deflection and transverse cooling. This represents the first laser cooling of a Hydride molecule. This is a crucial step towards the creation of new cold molecular samples for a variety of scientific applications. In the final chapter, I will change gears, and introduce new ideas for the detection of scalar field dark matter. While this variety of dark matter is typically searched for using atomic clocks, I will show that the same coupling also leads to anomalous acceleration of test masses. This acceleration would be detectable using both a network of precision acceleration sensors known as the IGETS network, and by the LIGO observatory. This new technique will compliment existing search strategies, and has higher sensitivity for a wide region of parameter space.

Population III (Pop III) stars are the first generation stars forming after the big bang from primordial gas. This dissertation is focused on the various processes that suppress and delay the formation of Pop III stars in the universe and their implications for the observations. We studied the impacts of the Lyman-Werner (LW) radiation that dissociates molecular hydrogen, baryon-dark matter streaming velocity introduced at recombination, ionizing radiation from nearby galaxies, and a model for the composition of dark matter known as the fuzzy dark matter on the formation of Pop III stars. Firstly, we take a closer look at the critical halo mass (Mcrit) that is the typical minimum dark matter halo mass needed to host cold dense gas to form the first stars using cosmological hydrodynamical simulations. LW radiation that dissociates molecular hydrogen and the baryon-dark matter streaming velocity both delay the formation of Pop III stars by increasing the critical halo mass. We describe our simulation suite with varying levels of LW radiation and streaming velocity to provide a fit for Mcrit as a function of LW radiation, streaming velocity, and redshift which can be used in semi-analytic models of early galaxy formation to make predictions for observations. Secondly, we explore a possible mechanism for the formation of large clusters of Pop III stars: a nearby ionizing source that ionizes a late forming halo, delaying its collapse until the halo is sufficiently large enough that the core can self-shield and suffer runaway collapse. We use numerical simulations to examine the fragmentation of the gas near the runaway collapse using the simple estimates and sink particles to show that the number of fragments is generally small, at most a handful, and that the mass accretion rate on the fragments is of order 10⁻³ Msun/yr. This rate is sufficiently high enough that the descent on the main sequence (and hence the suppression of accretion) is delayed until the stellar masses are of order 100-1000 Msun, but not high enough to produce direct collapse black holes of mass ~ 10⁵ Msun. The resulting clusters are larger than those produced in minihalos but are still likely to fall short of being easily detectable in James Webb Space Telescope blind fields. Finally, we investigate the formation of the first stars and galaxies in a fuzzy dark matter cosmology. Fuzzy dark matter, made up of ultra-light axions of mass ~ 10⁻²² eV, is a proposed alternative to the standard cold dark matter to solve its apparent small-scale problems. Its large de Broglie wavelength, of the order of kpc, results in the suppression of small-scale matter power, thus delaying the formation of the first stars and galaxies to lower redshift in much more massive halos. Therefore, first stars can be used to put very strong constraints on the mass of the fuzzy dark matter. We describe our cosmological simulations that accurately evolve the fuzzy dark matter distribution to study the formation of the first stars and galaxies.

This work presents the search for Dark Matter particles associated with the Higgs Boson decaying into a b b-bar quark pair. The dark matter search result is based on proton-proton collision data collected at a center-of-mass energy of 13 TeV by the ATLAS detector during Run II. The results are interpreted in the context of a simplified model (Z’-2HDM) which describes the interaction of dark matter and standard model particles via new heavy mediator particles. The new powerful Higgs tagging techniques, which exploit the jet substructure and heavy flavor information to a large extent, are developed to improve the search sensitivity of the search. The target physics signals are signature with an optimized search region and interpreted with background estimation result statistically.

In this dissertation, we develop two novel methods for studying the nature of the Milky Way's dark matter halo. In both cases, we rely on the relationship between the dark matter halo's gravitational potential and the orbital structure it supports. The first method explores the morphology of stellar streams orbiting in non-spherical gravitational potentials. When globular clusters or dwarf galaxies fall into the Milky Way, tidal forces shred them into long filaments of stars called stellar streams. We show that in non-spherical potentials, stream morphologies are heavily dependent on the characteristics of the progenitor's orbit. Flattened axisymmetric galactic potentials, for example, are known to host minor orbit families surrounding special orbits with commensurable frequencies. The behavior of orbits that belong to these orbit families is fundamentally different from that of typical orbits with non-commensurable frequencies. We show that streams evolving near the boundaries, or separatrices, between orbit families, may become fanned out, develop a bifurcation, or both. We utilize perturbation theory to estimate the timescale of this effect and the likelihood of a stream evolving close enough to a separatrix to be affected by it. Next, we study the dynamical reasons for stream fanning and bifurcations near resonances, and find that each morphological outcome has a slightly different dynamical cause. Using a novel numerical approach for measuring the libration frequencies of resonant and near-resonant orbits, we reveal that fans come about due to a large spread in the libration frequencies near a separatrix, whereas bifurcations arise when a separatrix splits the orbital distribution of the stellar stream between two (or more) distinct orbit families. We then demonstrate how these features can arise in streams on realistic galactic orbits, in realistic galactic potentials, over timescales as short as 2-3 Gyr, and discuss how this might be used to constrain the global shape of the Milky Way's gravitational potential. The second method studied in this dissertation enables dynamical tests of a dark matter candidate known as Fuzzy (or Ultra-Light) Dark Matter. Our method relies on a wave generalization of the classic Schwarzschild approach for constructing self-consistent halos -- such a halo consists of a suitable superposition of waves instead of particle orbits, chosen to yield a desired mean density profile. As an illustration, we apply the method to spherically symmetric halos. We derive an analytic relation between the particle distribution function and the wave superposition amplitudes, and show how it simplifies in the high energy (WKB) limit. We verify the stability of such constructed halos by numerically evolving the Schrodinger-Poisson system. The proposed algorithm provides an efficient and accurate way to simulate the time-dependent halo substructures from wave interference, and to test how they will affect dynamical tracers or other observables in a galaxy. The dissertation concludes with a brief discussion of the future prospects of these two methods, especially in the context of upcoming ground- and space-based missions like Rubin LSST and the Roman Space Telescope.

A wide array of cosmological and astrophysical observations support the existence of dark matter. More precisely, temperature anisotropy measurements of the cosmic microwave background (CMB) estimate that the current dark matter mass density is about five times that of the visible Universe. However, the nature of dark matter is not yet understood, inspiring numerous theoretical candidates. One popular candidate is the weakly-interacting massive particles or WIMPs that interact with standard model particles on the electroweak scale and could have the correct relic abundance today. Experiments such as XENON1T and XENONnT are designed to search for WIMPs on Earth using the dual-phase liquid xenon Time Projection Chamber (LXeTPC) technology. The XENON1T experiment operated until Dec. 2018 and had made the world-leading upper limits for WIMP-nucleus interactions at the time. Its successor, the XENONnT experiment, has been commissioned since 2021 and has taken data for its first science run. This thesis presents the commissioning data and the first science-run data analysis. This thesis describes an essential facet of the XENON1T and XENONnT experiments: how, step by step, the most elementary signals of single photons are reconstructed into events. Each event represents a particle interaction in the detector, including those from rare physical processes. This includes several technical developments with signal processing and simulation software that enable accurate reconstruction of signals and precisely evaluate the effect of various types of remaining miss-reconstruction. Furthermore, this thesis will present two analyses developed to search for rare events in XENON1T, only possible with an accurate and precise understanding of the event reconstruction. One is to search for ⁸𝐁 Solar neutrino events via 𝐂𝐄𝜈𝐍𝐒 process and low mass WIMPs by characterizing reconstruction efficiency and additional background at a lower energy threshold. The spin-independent DM-nucleus interaction is improved in the mass range between 3𝐆𝐞𝐕𝑐² and 11𝐆𝐞𝐕𝑐² by as much as an order of magnitude from the previous world-leading result, using data from the XENON1T experiment. The other is the search for the neutrinoless double-beta decay at its 𝑄-value, 𝑄_𝛽𝛽 = (2457.83$\pm$0.37)\,keV. The analysis demonstrated that the relative energy resolution at one 𝝈/𝝁 is as low as (0.80±$0.02) % in its one-ton fiducial mass, and for single-site interactions at 𝑄_𝛽𝛽, a world-leading resolution in 𝐋𝐗e experiment that enhance the experimental sensitivity to the neutrinoless double-beta decay events.

This thesis describes research I conducted within the XENON program of dark matter searches. In particular, I focus on contributions I made to the development of a novel system for purifying liquid xenon employed in XENONnT, to the reconstruction and modeling of electronic and nuclear recoil signals by fitting calibration data, and in the employment of these tools to world-leading physics searches for spin-dependent DM-nucleus scattering and coherent neutrino-nucleus scattering from boron-8 solar neutrinos.

Thesis (doctoral)--Rijksuniversiteit Groningen, 1997. / Includes bibliographical references.

This thesis is devoted to the study of the nature of Dark Matter (DM). To this end we investigate both its generation mechanisms and detection possibilities. We mainly focus on interesting simple models and follow closely experimental constraints, in order to reveal the features of DM as model-independently as possible.<p><p><p><p><p>Throughout the whole thesis, we consider the framework of standard cosmology, which is first introduced in Chapter.1 (and supplemented in Appendices). Background knowledges of DM physics from the cosmological and experimental aspects are given in Chapter.2 and Chapter.3, respectively. <p><p><p>Following the scenario that a hidden sector, including DM particles, might decouple from the Standard Model (SM) sector at a very early time of the Universe, we study how through a portal interaction such a hidden sector can be created by the SM sector to yield the proper relic density of dark matter. In Chapter.4 we discuss the case of a massless portal using the gauge kinetic mixing model. It turns out that there are four basic ways to achieve the observed DM relic density for both massless and massive mediator cases: freeze-in from SM sector, reannihilation determined by the balance of the two sectors, freeze-out with hidden or portal interactions. Various models with massive portals, especially $Z'$ and scalar portals, are then explored in Chapter.5. Provided that DM annihilation within the hidden sector is kinetically allowed, similar conclusions would appear. If there is no hidden annihilation for DM, only the first and last ways are allowed. Nevertheless, chemical thermalization in hidden sector can still influence the results significantly.<p><p>In Chapter.6, we explore the hypothesis that dark matter particles partially annihilate to photons via a new heavy charged particle which is also "gauged" under SU(3)_C. By applying this hypothesis to the claimed<p>Fermi-LAT 130 GeV gamma line, it is showed that the correct dark matter relic density could be naturally obtained from the gluon channel and how for such a class of models the cosmic antiproton, diffuse gamma-ray, direct detection and LHC constraints<p>are fully correlated. <p><p><p>In Chapter.8, concluding remarks and perspectives for future DM research are presented. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Orientador: Marcelo Moraes Guzzo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T10:36:59Z (GMT). No. of bitstreams: 1 Ferreira_CesarPeixoto_M.pdf: 5430137 bytes, checksum: 52b53b619a2021426f948ae3c70beb98 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho analisa-se uma das extensões do Modelo Padrão das Partículas Elementares, conhecida como Extensão 3-3-1\', e suas aplicações a Cosmologia. Esta classe de modelos constitui uma das mais enxutas extensões do Modelo Padrão, e possui entre as suas qualidades respostas a problemas deixados em aberto dentro do Modelo Padrão. Entre estes, lista-se o problema do numero de gerações e o problema da assimetria das massas dos quarks, respondidos através de um critério de consistência interna do modelo, a saber, o cancelamento das anomalias quirais. O modelo especifico escolhido para estudo foi o Modelo 3-3-1 com neutrinos de m~ao direita (3-3-1RH), e todas as suas principais características são analisadas. Para aplicações a Cosmologia, o 3-3-1 foi analisado em suas aplicações ao problema da Matéria Escura. Neste caso, analisar-se-~ao candidatos a Matéria Escura em uma extensão do 3-3-1, chamada Modelo 3-3-1 Left-Right (3L3R). Estes candidatos s~ao neutrinos estereis de massa na escala keV, e a eles s~ao aplicados os limites cosmológicos impostos por Decaimento em Raio-X, Neff e Abundância de matéria escura. 3 casos foram analisados: (1) Desacoplamento dos neutrinos estereis anterior a aniquilação dos múons. (2) Desacoplamento anterior a aniquilação dos pons; (3) Desacoplamento anterior a Hadronização. A aplicação dos limites supracitados revelou que estes neutrinos n~ao sofrem de restrições de decaimentos em Raio-X. Para cada um dos 3 casos, o valor de Neff por neutrino estéril foi de 3.69, 3.53 e 3.09, respectivamente. Como experimentalmente, Neff = 3:280:28, conclui-se que em 2 dos casos, apenas 1 neutrino novo e admitido, e no caso restante os 3 neutrinos novos do 3L3R s~ao possíveis. Por m, o calculo de abundância revelou um excesso destes neutrinos, usando-se o método para calculo de abundância de neutrinos ativos. A abundância calculada e maior que a medida experimentalmente em todos os casos posseis para o modelo, mesmo considerando-se um caso limite. Dessa forma, conclui-se que algum mecanismo alternativo de diluição de densidade destes neutrinos e necessário / Abstract: In this dissertation, one of the extensions of the Standard Model of Elementary Particles(SM), known as the '3-3-1 Extension\', and its aplication to Cosmology are analysed. This class of models constitutes one of the most economical extensions of the Standard Model, and have among its qualities answers to open problems within the SM. Among them, we mention the generation problem and the quark mass assymetry problem. Both of these problems are answered trough the use of a internal consistency criterion of the model: The cancelation of chiral anomalies. The model chosen for study was the 3-3-1 Model with right handed neutrinos (3- 3-1RH), and all its main caracteristics are analysed. To aplications to Cosmology, the 3-3-1 was studied within the Dark Matter problem. In this case, we analyse dark matter candidates in one extension of the 3-3-1, known as the Left-Right 3- 3-1 Model (3L3R). These candidates are sterile neutrinos with keV masses, and to them cosmological limits are applied. These limits are the decays into X-Rays, Neff and Dark Matter Abundance. 3 cases were analysed: (1) Decoupling of the sterile neutrinos before muon annihilation; (2) Decoupling before pion annihilation; (3) Decoupling before Hadronization. The application of the limits mentioned above revealed that these neutrinos do not, at the moment, have any restrictions coming from decays into X-Rays, because this kind of decay is forbidden in the 3L3R. For each of the 3 cases, Neff had the value of 3.69, 3.53 e 3.09, respectively. When this is compared with the experimental value, Neff = 3:28 0:28, we conclude that in two cases, only one sterile neutrino is roughly allowed. In the remaining case, all 3 new neutrinos of the 3L3R are possible. The calculation of abundance revelead an excess of these neutrinos, using the method that is used to calculate abundance of active neutrinos. The calculated abundance is bigger than the experimentally determined in all possible cases, even when we consider a limit case. We conclude that some alternative mechanism for density dilution is necessary / Mestrado / Física / Mestre em Física