In the standard model of cosmology (ΛCDM) the first stars, star clusters, and galaxies are expected to have formed in short bursts of star formation in low-mass dark matter halos at high redshifts (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%5Csim%20%5C,6-10" data-classname="equation_inline" />). Up to this point, attempts to predict the properties and abundances of these luminous objects have made use of numerically expensive cosmological simulations. On top of being numerically expensive, these simulations often lack the required sub-parsec resolution needed to resolve the formation of compact star clusters and/or neglect possibly dominant stellar feedback processes. Motivated by this, I introduce Anaxagoras, as far as I know the most detailed analytical ab initio model of starbursts in low-mass halos to date. The model incorporates sub-models for gas cooling (including a new determination of the H2-cooling threshold in minihalos), central gas accretion and disk formation (using a new selfsimilarsolution), stellar feedback from radiation pressure (direct stellar radiation, Lyman-<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Calpha" data-classname="equation_inline" data-title="" /> scattering in H I, and multiple scattering of IR photons by dust), stellar winds, expanding HII regions, and (crudely) supernovae. The resulting star formation efficiency is used to predict the fraction of stars that remain gravitationally bound in a cluster following gas expulsion, andwhat fraction escape the central region of the halo, yet remain bound by the dark matter halo. I apply Anaxagoras to study star formation at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%3E%20%5C,6" data-classname="equation_inline" /> in satellite halos of the Milky Way using a halo merger tree code, as well as Population III (Pop III) star formation in minihalos. For the Milky Way setup, hundreds of galaxies are predicted to form with luminosities (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?L_%7B%5Crm%20V%7D%20%5C,%3C%5C,%20%5Crm%7Bfew%7D%5C,%20%5Ctimes%20%5C,%2010%5E4%20%5C:%20%5Crm%7BL%7D_%7B%5Codot%7D" data-classname="equation_inline" />), half-mass radii (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csim%2010-200%5C:%5Crm%20pc" data-classname="equation_inline" />), mass-to-light ratios (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?M/L_%7B%5Crm%20V%7D%20%5Csim%20100%20-%20%5Crm%7Bfew%7D%20%5C,%5Ctimes%5C,%2010%5E3%20%5C:%5Crm%7BM%7D_%7B%5Codot%7D/%5Crm%7BL%7D_%7B%5Codot%7D" data-classname="equation" />), and ages (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?13.18%5E%7B+0.29%7D_%7B-0.31%7D%5C:%5Crm%20Gyrs" data-classname="equation_inline" data-title="" />) in good agreement with the observed local population of Ultra-Faint Dwarfs. This shows that ΛCDM is able to explain the properties ofthe faintest dwarf galaxies without fine-tuning. Furthermore, at least ~ 40 compact (initial half-mass radii <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csim%200.1-5%5C;%5Crm%7Bpc%7D" data-classname="equation_inline" />), old (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?13.27%5E%7B+0.21%7D_%7B-0.39%7D%5C:%5Crm%20Gyrs" data-classname="equation_inline" />) globular cluster (GC) candidates with initial stellar masses <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?10%5E5%20-%2010%5E6%20%5C:%20%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" />  are predicted to form at the center of low-mass halos, and could survive to the present-day and explain at least a fraction of the observed metal-poor GCs. Their properties are consistent with recent candidates for GCs residing in dark matter halos. Thus, Anaxagoras lends support to the viability of the scenario of GC formation in minihalos. Finally, the formation of Population III (Pop III) stars in minihalos is studied, with the conclusion that if Pop III stars are not overly massive (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?25%5C:%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" />) between ~ 1 − 30 stars could form per minihalo at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%3E%20%5C,20" data-classname="equation_inline" />, with the number increasing to ~ 10 − 500 stars per minihalo at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%3C%5C,15" data-classname="equation_inline" /> as Lyman-Werner feedback delay star formation until halos reach larger masses. In the case where Pop III stars are more massive (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?140%5C:%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" data-title="" />) most minihalos form just a single star. Due to self-shielding of H2 in minihalos, I find that the cosmological Lyman-Werner background is insufficient to produce Pop III galaxies in atomic-cooling halos, with the implication that the number of massive Pop III galaxies/star clusters in the early Universe has been greatly overestimated in the literature that ignores self-shielding.

In this study, we investigate the feasibility of Feebly Interacting Massive particles (FIMP) as possible candidates to constitute the observed Dark Matter abundance in the universe. FIMPs are particles that couple very feebly with known particles in the Standard Model (SM). As such, they do not attain thermal equilibrium with the baryon abundant environment in the early universe before Nucleosynthesis. In contrast to a freeze-out mechanism common for Weakly Interacting Massive Particles (WIMP) as DM candidates, FIMPs are produced by the so-called freeze-in mechanism that we will describe in this study. The purpose of this study is to investigate how the Coleman Weinberg (C-W) mechanism affects the FIMP [freeze-in] mechanism. We specifically consider a minimal extension of SM in which an Electroweak Singlet-scalar ($S$) couples only to the Higgs-boson ($H$); This is called the Higgs-portal mechanism. We study the C-W effective potentials for the Higgs and Dark-scalar singlet and their implications on FIMP mechanism.Using these, we focus on the High-temperature production of the DM with just the $HH\mapsto SS$ to compute the reaction rates, comparing Bose-Einstein statistics ($\Gamma_{HH\mapsto S S}^{B-E}$) to Maxwell-Boltzmann statistics $\Gamma_{HH\mapsto S S}^{M-B}$. We employ only $\Gamma_{HH\mapsto S S}^{B-E}$ to compute DM relic abundance ($Y$) at several Dark-scalar masses ($m_S$) as a function of coupling $k$, establishing that Higgs-Dark scalar coupling $k$ $\mapsto$ $k_{DM}$ corresponding to actual DM abundance lies in between ${10}^{-8.7}$ and ${10}^{-8}$, i.e. ${10}^{-8.7}&lt;k_{DM}&lt;="" div=""&gt; / I denna studie undersöker vi mycket svagt interagerande massiva partiklar (FIMP) som möjliga kandidater till den observerade mängden av mörk materia i universum. FIMP:er är partiklar som interagerar väldigt svagt med de kända partiklarna i Standarmodellen (SM). Som sådana uppnår de ej termisk jämvikt med den baryonrika omgivningen i det tidiga universumet innan nukleosyntes sker. I kontrast med en frys-ut mekanism vanligt för svagt interagerade massiva partiklar (WIMPS) som DM kandidater, så produceras FIMP:er av en så kallad frys-in mekanism som vi skall beskriva i denna studie. Syftet med studien är att undersöka hur Coleman Weinberg (C-W) mekanismen påverkar frys-in mekanismen för FIMP:er. Vi tar särskilt hänsyn till en minimal utvidgning av SM i vilken en Elektrosvag singlettskalär ($S$) interagerar med endast Higgsbosonen. Denna mekanism kallas för Higgs-portalmekanism. Vi studerar de C-W effektiva pontetialerna för higgs och mörk-skalärsingletten och deras implikationer för FIMPmekanismen. När vi använder dessa, så fokuserar vi på högtemperatursproduktion av DM med endast $HH\mapsto SS$ för att beräkna reaktionshastigheter, och jämför Bose-Einstein statistik ($\Gamma_{HH\mapsto S S}^{B-E}$) med Maxwell-Boltzmann statistik $\Gamma_{HH\mapsto S S}^{M-B}$. Vi använder endast $\Gamma_{HH\mapsto S S}^{B-E}$ för att beräkna kvarvarande DM mängd ($Y$) för flera mörk-skalärmassor ($m_S$) som en funktion av interaktion $k$, vilket slår fast att Higgs-Mörk skalär interaktionen $k$ $\mapsto$ $k_{DM}$ som korresponderar mot den faktiska DM mängden ligger mellan ${10}^{-8.7}$ and ${10}^{-8}$, i.e. ${10}^{-8.7}&lt;k_{DM}&lt;="" div=""&gt;

Dunkle Materie bindet etwa 24 % der gesamten Energie im Universum. Bis heute ist jedoch dessen Ursprung nicht bekannt. Untersuchungen von Galaxien und kosmologischen Messungen deuten auf Dunkle Materie hin. Ein Kandidat für Dunkle Materie ist das sogenannte Weakly Interactive Massive Particle (WIMP), welches nur der Schwerkraft und der schwachen Wechselwirkung unterliegt. Eines dieser supersymmetrischen Teilchen ist das Neutralino. Das Ziel dieser Arbeit ist es, nach Dunkler Materie in dieser Form zu suchen. Aufgrund seiner Nähe sowie der hohen Dichte an Dunkler Materie bietet das Zentrum unserer Galaxie besondere Möglichkeiten zur Suche nach diesen Teilchen. Es wird vermutet, dass Neutralinos miteinander wechselwirken, dabei in Teilchen des Standard Modells zerfallen und so Photonen mit hohen Energien entstehen. Die Suche nach hochenergetischen Gammastrahlen in der Nähe des Galaktischen Zentrums kann folglich das Rätsel der Dunklen Materie lösen. Das Gammastrahlenobservatorium VERITAS hat das Galaktische Zentrum für etwa 108 Stunden beobachtet. Diese Daten wurden mittels einer unbinned Likelihood-Analyse auf die Existenz von Dunkler Materie untersucht. Da VERITAS das Galaktische Zentrum bei geringer Elevation beobachtet, können nur Gammastrahlen in einem Energiebereich zwischen 4 und 70 TeV detektiert werden. Die Analysemethode modelliert sowohl die räumliche Verteilung der Dunklen Materie als auch das Gammastrahlenspektrum. Der Beitrag der Gammastrahlen, welcher nicht von Dunkler Materie erzeugt wird, ist mittels einer punktförmigen Quelle modelliert. Zum Schluss wird der Untergrund mit realen Daten außerhalb des Galaktischen Zentrums abgeschätzt. Im Energiebereich zwischen 4 und 100 TeV wurden keine Signale der Dunklen Materie gefunden. Obere Grenzwerte für den Wechselwirkungsquerschnitt der WIMPs ergeben ⟨σv⟩ < (6.6 − 7.6) × 10−25 cm^3 oberhalb von 70 TeV in einem 95-prozentigen Erwartungsintervall. / Dark matter accounts for 24% of the universe’s energy, but the form in which it is stored is currently unknown. Understanding what form this matter takes is one of the major unsolved mysteries of modern physics. Much evidence exists for dark matter in the measurements of galaxies, dwarf galaxies, galaxy clusters, and cosmological measurements. One theory posits dark matter is a new undiscovered particle that only interacts via gravity and the weak force, called a weakly interacting massive particle (WIMP). One WIMP candidate is a supersymmetric particle called a neutralino. The objective of this thesis is to search for these dark matter particles, and attempt to measure their mass and cross section. Dark matter particles appear to concentrate in most galaxy-scale gravitational wells. One region of space that is both nearby and assumed to have a high density of dark matter is the center of our own galaxy. The neutralino is expected to annihilate into Standard Model particles, which may decay into photons. Therefore, a search for gamma rays near the Galactic Center may uncover the presence of dark matter. 108 hours of VERITAS gamma-ray observations of the Galactic Center are used in an unbinned likelihood analysis to search for dark matter. The Galactic Center’s low elevation results in VERITAS observing gamma rays in the 4–70 TeV energy range. The analysis used in this thesis consists of modeling the halo of dark matter at the Galactic Center, as well as the spectrum of gamma rays produced when two WIMPs annihilate. A point source is added to model the non-dark-matter gamma-ray emission detected from the Galactic Center. Background models are constructed from data of separate off-Galactic-Center observations. No dark matter signal is found in the 4–100 TeV mass range. Upper limits on the WIMP’s velocity-averaged cross section have been calculated, which above 70 TeV result in new limits of ⟨σv⟩ < (6.6 − 7.6) × 10−25 cm3 at the 95% confidence level.

L’expérience H.E.S.S. (High Energy Spectroscopic System) composée de cinq télescopes Tcherenkov observe le ciel en rayons gamma au-delà d'une centaine de GeV jusqu'à plusieurs dizaines de TeV. Les rayons gamma sont produits par des phénomènes non-thermiques parmi les plus violents dans l'univers au voisinage d'objets astrophysique comme les pulsars, supernovae ou trous noirs, mais pourraient être également produits par l'annihilation de particules de matière noire.De nombreuses sondes cosmologiques et astrophysiques suggèrent que 85% de la matière dans l'Univers est d'origine inconnue. Cette matière appelée matière noire, de nature non baryonique, serait constituée de particules non encore découvertes dont les candidats privilégiés seraient des particules massives interagissant faiblement (WIMPs) avec la matière ordinaire, particules prédites au-delà du Modèle Standard de la physique des particules.Des particules de matière noire peuvent s'annihiler en particules du Modèle Standard dans les régions denses de l'Univers. Parmi les produits d'annihilations se trouvent les photons dont la détection à hautes énergies par des télescopes au sol à effet Tcherenkov pourrait apporter des informations uniques sur la nature de la matière noire.H.E.S.S. observe des régions du ciel dense en matière noire comme le Centre Galactique et des galaxies naines satellites de la Voie Lactée.Une interprétation d'un excès de rayons gamma détecté au Centre Galactique par H.E.S.S. en termes d’accélération de protons par une population de pulsars millisecondes est présenté.10 ans d'observations du Centre Galactique avec le réseau H.E.S.S. I de quatre télescopes, cinq ans de prise de données vers la région du Centre Galactique avec le réseau complet H.E.S.S. II, et un jeu de deux ans de données vers des galaxies naines découvertes récemment sont analysés. Les recherches de signaux d'annihilation de matière noire vers ces cibles ont produit les limites plus fortes à présent sur la section efficace d'annihilation de matière noire dans la plage en masse du TeV. Le potentiel de détection de matière noire avec le futur réseau de télescopes CTA (Cherenkov Telescope Array) vers la région central du halo Galactique est étudiés. / The H.E.S.S. (High Energy Spectroscopic System) experiment is an array of five Cherenkov telescopes that observe the sky in gamma-rays from about 100 GeV up to several ten TeV.Gamma rays are produced in violent non-thermal phenomena in the Universe in the neighborhood of pulsars, supernovae, black holes, ..., and could also be produced by the annihilation of dark matter particles.Numerous cosmological and astrophysical probes suggest that 85% of the total matter budget in the Universe is of unknown origin. This component of matter known as dark matter is non baryonic and could consist of yet undiscovered particles which privileged candidates are arguably massive particles with electroweak couplings with ordinary matter (WIMPs).Dark matter particles may annihilate into Standard Model particles in dense regions of the Universe. Among the annihilation products are photons which detection at high energy with ground-based Cherenkov telescopes could bring unique information on the nature of the dark matter.H.E.S.S. observes dark-matter-dense regions of the sky such as the Galactic Center and dwarf galaxy satellites of the Milky Way. A study on the interpretation of an excess of gamma-rays detected by H.E.S.S. at the Galactic Center in terms of acceleration of protons by a population of unresolved millisecond pulsars is performed.10 years of observations of the Galactic Center with the four-telescope H.E.S.S.-I array, five years of data taking towards the Galactic Center region with the full H.E.S.S.-II array and a two-years dataset towards newly discovered dwarf spheroidal galaxies are analyzed. The search for dark matter annihilation signals towards these targets provided the strongest limits so far on dark matter annihilation cross section in gamma rays of TeV energies. The potential of dark matter detection with the upcoming Cherenkov Telescope Array (CTA) towards the inner Galactic halo are studied. They may annihilate into Standard Model particles in dense regions of the Universe. Among the annihilation products are high energy photons. The detection of these photons with ground-based Cherenkov telescopes may reveal the nature of the dark matter. H.E.S.S. have observed some dark-matter-dense regions of the sky likethe Galactic Center and dwarf galaxies satellites of the Milky Way. In this work 10 years of observations of the Galactic Center with the four-telescopes H.E.S.S.-I array, five years of data taking towards the Galactic Center region with the full H.E.S.S.-II array and a two-years dataset towards newly discovered dwarf spheroidal galaxies are analyzed. The searches for dark matter annihilation signals towards these targets produced the strongest limits so far on dark matter annihilation cross section in gamma rays of TeV energies.Perspectives of dark matter detection with the future array CTA (Cherenkov Telescope Array) towards the inner Galactic halo are also discussed. A study on the interpretation of an excess of gamma-rays detected by H.E.S.S. at the Galactic Center in terms of acceleration of protons by a population of unresolved millisecond pulsars complements the dark matter searches.

L’avènement du séquençage métagénomique aléatoire a révolutionné la microbiologie en permettant la caractérisation sans culture préalable de communautés microbiennes complexes telles que le microbiote intestinal humain. Des outils bioinformatiques récemment développés atteignent une résolution au niveau de la souche en recensant des gènes accessoires ou en capturant des variants nucléotidiques (SNPs). Toutefois, ces outils sont limités par l’étendue des génomes de référence disponibles qui sont loin de couvrir toute la variabilité microbienne. En effet, de nombreuses espèces n’ont pas encore été séquencées ou sont représentées par seulement quelques génomes.La création de catalogues de gènes non redondants par assemblage de novo suivie du regroupement des gènes co-abondants révèlent une partie de la matière noire microbienne en reconstituant le répertoire de gènes d’espèces potentiellement inconnues. Bien que les méthodes existantes identifient avec précision les gènes core présents dans toutes les souches d’une espèce, elles omettent de nombreux gènes accessoires ou les divisent en petits groupes de gènes qui ne sont pas associés aux core génomes. Or, capturer ces gènes accessoires est indispensable en recherche clinique et épidémiologique car ces derniers assurent des fonctions spécifiques à certaines souches telles que la pathogénicité ou la résistance aux antibiotiques.Lors de cette thèse, nous avons développé MSPminer, un logiciel performant qui reconstitue et structure des pan-génomes d’espèces métagénomiques (ou MSPs pour Metagenomic Species Pan-genomes) en regroupant les gènes co-abondants dans un ensemble d’échantillons métagénomiques. MSPminer s’appuie sur une nouvelle mesure robuste de la proportionnalité couplée à un classificateur empirique pour regrouper et distinguer les gènes core mais aussi les gènes accessoires des espèces microbiennes.Grâce à MSPminer, nous avons structuré un catalogue de 9,9 millions de gènes du microbiote intestinal humain en 1 661 MSPs. L’homogénéité de l’annotation taxonomique, de la composition nucléotidique ainsi que la présence de gènes essentiels indiquent que les MSPs ne correspondent pas à des chimères mais à des objets biologiquement cohérents regroupant des gènes provenant de la même espèce. Parmi ces MSPs, 1 301 (78%) n’ont pas pu être annotées au niveau espèce montrant que de nombreux microorganismes colonisant l’intestin humain demeurent inconnus malgré les progrès substantiels des techniques de culture microbienne. Remarquablement, les MSPs capturent bien plus de gènes que les clusters générés par les outils existants tout en garantissant une spécificité élevée.Cet ensemble de MSPs peut d’ores et déjà être utilisé pour le profilage taxonomique et la découverte de biomarqueurs dans des échantillons de selles humaines. Ainsi, nous tirons parti des MSPs pour comparer l’impact sur le microbiote intestinal des deux principaux types de chirurgie bariatrique, la gastrectomie par laparoscopie (LSG) et la dérivation gastrique de Roux-en-Y (LRYGB). Enfin, les MSPs ouvrent la voie à des analyses au niveau souche. Dans une autre cohorte, nous avons mis en évidence l’existence de sous-espèces associées à l’origine géographique de l’hôte en étudiant les profils de présence/absence des gènes accessoires groupés dans les MSPs. / The advent of shotgun metagenomic sequencing has revolutionized microbiology by allowing culture-independent characterization of complex microbial communities such as the human gut microbiota. Recently developed bioinformatics tools achieved strain-level resolution by making a census of accessory genes or by capturing nucleotide variants (SNPs). Yet, these tools are hampered by the extent of available reference genomes which are far from covering all the microbial variability. Indeed, many species are still not sequenced or are represented by only few genomes.Building of non-redundant gene catalogs followed by the binning of co-abundant genes reveals a part of the microbial dark matter by reconstituting the gene repertoire of species potentially unknown. While existing methods accurately identify core genes present in all the strains of a species, they miss many accessory genes or split them into small gene groups that remain unassociated to core genomes. However, capturing these accessory genes is essential in clinical research and epidemiology because they provide functions specific to certain strains such as pathogenicity or antibiotic resistance.In this thesis, we developed MSPminer, a computationally efficient software tool that reconstitutes Metagenomic Species Pan-genomes (MSPs) by binning co-abundant genes across metagenomic samples. MSPminer relies on a new robust measure of proportionality coupled with an empirical classifier to group and distinguish not only species core genes but accessory genes also.With MSPminer, we structured a catalog made up of 9.9 million genes of the human gut microbiota in 1 661 MSPs. The homogeneity of the taxonomic annotation, of the nucleotide composition as well as the presence of essential genes indicate that the MSPs do not correspond to chimeras but to biologically consistent objects grouping genes from the same species. Among these MSPs, 1 301 (78%) could not be annotated at species level showing that many microorganisms colonizing the human intestinal tract are still unknown despite the substantial improvements of microbial culture techniques. Remarkably, MSPs capture more genes than clusters generated by existing tools while ensuring high specificity.This set of MSPs can be readily used for taxonomic profiling and biomarkers discovery in human gut metagenomic samples. In this way, we take advantage of the MSPs to compare the impact of two main types of surgeries, the laparoscopic sleeve gastrectomy (LSG) and the Roux-En-Y gastric bypass (LRYGB). Finally, the MSPs open the way to strain-level analyses. In another cohort, we identified subspecies associated the host geographical origin by studying presence/absence patterns of the accessory genes grouped in the MSPs.

Pas de résumé en français / In experiments looking for rare events, like neutrinoless double beta decay (DBD0v) and dark matter search (DM), one of the main issues is to increase the experimental sensitivity through the material selection and production. In the specific the background contribution coming from the materials used for the detector realization has to be minimized. Moreover the net reduction of the background produced by the bulk part of the apparatus has raised concerns about the background contribution coming from the surfaces. Many procedures and techniques were developed during the last years in order to remove and to minimize the presence of possible contaminants on detector surfaces. To succeed in this strategy a big effort was put in defining all possible mechanisms that lead to surface contaminations, as well as specific cleaning procedures, which are able to reduce and control the surface radioactivity. The presence in air and gases of possible radioactive elements that can stick on the detector surfaces can lead to a recontamination process that will vanish all the applied cleaning procedures. Here is presented and analyzed the contribution to the background of rare events experiments like CUORE (DBD0v) and EDELWEISS (DM) produced by an exposure of their detector components to a big activity of 222Rn, radioactive daughter isotope from the 238U chain

No description available.

While holding a firm position in popular culture and science fiction, Dark Matter (DM) is nonetheless a highly relevant topic at the forefront of modern particle physics. We study the applicability of characterizing DM particle candidates SUSY neutralino and sneutrino using Deep Learning (DL) methods. We focus on the monojet and mono-Z signatures and the emergence of missing transverse energy as the result of the undetectable DM candidates. Based on kinematic distributions of outgoing particles as input, a DM candidate classifier is built for each signature, along with a DM mass regressor. The DM candidate classifier obtained near perfect accuracy of 0.995 for the monojet, and 0.978 for mono-Z signature. The monojet and mono-Z mass regressors achieved a Mean Absolute Percentage Error (MAPE) of 17.9 % and 8.5 % respectively. Furthermore, we discuss both the shortcomings and simplification that our choice of model implied, as well as an interpretation of the results. Finally, we debate the prospects of DL in the discovery of new physics and it's use in experiments.

In this thesis, two applications of dimensional deconstruction are studied. The first application is a model for neutrino oscillations in the presence of a large decon- structed extra dimension. In the second application, Kaluza{Klein dark matter from a latticized universal extra dimension is studied. The goal of these projects have been twofold. First, to see whether it is possible to reproduce the relevant features of the higher-dimensional continuum theory, and second, to examine the effect of the latticization in experiments. In addition, an introduction to the the- ory of dimensional deconstruction as well as to the theory of continuous extra dimensions is given. Furthermore, the various higher-dimensional models, such as Arkani-Hamed{Dvali{Dimopolous (ADD) models and models with universal extra dimensions, that have been intensively studied in recent years, are discussed. / QC 20101202

La matière sombre est considérée comme l'un des plus grands mystères dans la cosmologie moderne. En effet, on peut dire que l’on connaît plus sur ce que la matière sombre n'est pas que sur sa vraie nature. La collaboration SuperCDMS travaille sans répit pour réussir à faire la première détection directe de la matière sombre. À cet effet, la collaboration a eu recours à plusieurs expériences et simulations à diverses échelles, pouvant aller de l'usage d'un seul détecteur semi-conducteur, jusqu'à la création d'expériences à grande échelle qui cherchent à faire cette première détection directe de la matière sombre. Dans ce texte, on verra différentes méthodes pour nous aider à mieux comprendre les erreurs systématiques liées à la position du détecteur utilisé dans le cadre des expériences IMPACT@TUNL et IMPACT@MTL, soit l'usage des simulations et de la radiologie industrielle respectivement. On verra aussi comment l'implémentation de la méthode de réduction de variance connue comme échantillonnage préférentiel, peut aider à améliorer l'exécution des simulations de l'expérience à grande échelle planifiée pour le laboratoire canadien SNOLAB. En outre, on verra comment l'échantillonnage préférentiel s'avère utile non seulement pour mieux profiter des ressources disponibles pour la collaboration, mais aussi pour avoir une meilleure compréhension des source de bruits de fond qui seront présentes à SNOLAB, tels que les signaux générés par la désintégration radioactive de divers isotopes. / Dark matter is one of the biggest mysteries of modern-day cosmology. Simply put, we know much more about what it is not, rather than what it actually is. The SuperCDMS collaboration works relentlessly toward making the first direct detection of this type of matter. To this effect, multiple experiments and simulations have been performed, ranging from small-scale testing of the detectors to large-scale, long-term experiments, looking for the actual detection of dark matter. In this work, I will analyze different methods to help understand the systematic errors linked to detector position in regard to the small-scale experiments IMPACT@TUNL and IMPACT@MTL, through simulation and industrial radiography respectively. We will also see how the implementation of the variance reduction method known as importance sampling can be used to improve the simulation performance of the large-scale experiment in the Canadian laboratory SNOLAB. Additionally, we will see how this method can provide not only better management of the computing resources available to the collaboration, but also how it can be used to better the understanding of the background noises, such as the signals generated by radioactive decay of different isotopes, that will be present at SNOLAB.