Big Bang Nucleosynthesis (BBN), together with the analyses of the Cosmic Microwave Background (CMB) anisotropies, confirm what our day to day experience of life attests : antimatter is far less present than matter in the Universe. In addition, these observables also permit to evaluate that there exists about one proton for every 10^{10} photons present in the Universe. This is in contradiction with expectations coming from the standard hot big bang, where no distinction between matter and antimatter is made, and where subsequent annihilations would lead to equal matter and antimatter contents, at a level 10^{−10} smaller than the observed one. The Standard Model of fundamental interactions fails to explain this result, leading us to search for ‘Beyond the Standard Model’ physics. Among the possible mechanism which could be responsible for the creation of such a matter asymmetry, leptogenesis is particularly attractive because it only relies on the same ingredients previously introduced to generate neutrino masses. Unfortunatelly, this elegant proposal suffers from a major difficulty : it resists to any tentative of being probed by our low energy observables. In this thesis, we tackle the problem the other way around and propose a way to falsify this mechanism. Considering the type-I leptogenesis mechanism, i.e. a mechanism based on the asymmetric decay of right-handed neutrinos, in a left-right symmetric framework, we show that the observation of a right-handed gauge boson W_R at future colliders would rule out any possibility for such mechanism to be responsible of the matter asymmetry present in our Universe. Another intriguing question that analyses of the anisotropies of the CMB confirmed is the presence of a non-baryonic component of matter in our Universe, i.e. the dark matter. As hinted by observations of galactic rotation curves, it should copiously be present in our galactic halo, but is notoriously difficult to detect directly. We can take advantage on the fact that antimatter almost disappeared from our surroundings to detect the contamination of cosmic rays from standard sources the annihilation products of dark matter would produce. The second subject tackled in this work is the study of the imprints the Inert Doublet Modem (IDM) could leave in (charged) cosmic rays, namely positrons, antprotons and antideuterons. This model, first proposed to allow the Bout-Englert-Higgs particle to evade the Electroweak Precision Test (EWPT) measurements, introduces an additional scalar doublet which is inert in the sense that it does not couple directly to fermions. This latter property brings an additional virtue to this additional doublet : since it interacts weakly with particles, it can play the role of dark matter. This study will be done in the light of the data recently released by the PAMELA, ATIC and Fermi-GLAST collaborations, which reported e^± excesses in two different energy ranges.

A search for a diffuse flux of cosmic neutrinos with energies in excess of 1014 eV was performed using two years of AMANDA-II data, collected in 2003 and 2004. A 20% evenly distributed sub-sample of experimental data was used to verify the detector description and the analysis cuts. A very good agreement between this 20% sample and the background simulations was observed. The analysis was optimised for discovery, to a relatively low price in limit setting power. The background estimate for the livetime of the examined 80% sample is 0.035 ± 68% events with an additional 41% systematical uncertainty. The total neutrino flux needed for a 5σ discovery to be made with 50% probability was estimated to 3.4 ∙ 10-7 E-2 GeV s-1 sr-1 cm-2 equally distributed over the three flavours, taking statistical and systematic uncertainties in the background expectation and the signal efficiency into account. No experimental events survived the final discriminator cut. Hence, no ultra-high energy neutrino candidates were found in the examined sample. A 90% upper limit is placed on the total ultra-high energy neutrino flux at 2.8 ∙ 10-7 E-2 GeV s-1 sr-1 cm-2, taking both systematical and statistical uncertainties into account. The energy range in which 90% of the simulated E-2 signal is contained is 2.94 ∙ 1014 eV to 1.54 ∙ 1018 eV (central interval), assuming an equal distribution over the neutrino flavours at the Earth. The final acceptance is distributed as 48% electron neutrinos, 27% muon neutrinos, and 25% tau neutrinos. A set of models for the production of neutrinos in active galactic nuclei that predict spectra deviating from E-2 was excluded.

The solar minimum of 2009 has been identified as an exceptional event with regard to cosmic ray (CR)modulation, since conditions in the heliosphere have reached unprecedented quiet levels. This unique minimum has been observed by the Earth–orbiting satellite, PAMELA, launched in June, 2006, from which vast sets of accurate proton and electron preliminary observations have been made available. These simultaneous measurements from PAMELA provide the ideal opportunity to conduct an in–depth study of CR modulation, in particular charge–sign dependent modulation. In utilizing this opportunity, a three–dimensional, steady–state modulation model was used to reproduce a selection of consecutive PAMELA proton and electron spectra from 2006 to 2009. Thiswas done by assuming full drifts and simplified diffusion coefficients, where the rigidity dependence and absolute value of themean free paths for protons and electrons were sequentially adjusted below 3 GV and 300 MV, respectively. Care has been taken in calculating yearly–averaged current–sheet tilt angle and magnetic field values that correspond to the PAMELA spectra. Following this study where the numerical model was used to investigate the individual effects resulting from changes in the tilt angle, diffusion coefficients, and global drifts, it was found that all these modulation processes played significant roles in contributing to the total increase in CR intensities from 2006 to 2009, as was observed by PAMELA. Furthermore, the effect that drifts has on oppositely charged particles was also evident from the difference between the peak–shaped time profiles of protons and the flatter time profiles of electrons, as is expected for an A < 0 polarity cycle. Since protons, which drift into the heliosphere along the heliospheric current–sheet, haven’t yet reached maximum intensity levels by 2008, their intensities increased notably more than electrons toward the end of 2009. The time and energy dependence of the electron to proton ratios were also studied in order to further illustrate and quantify the effect of drifts during this remarkable solar minimum period. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2012.

The solar minimum of 2009 has been identified as an exceptional event with regard to cosmic ray (CR)modulation, since conditions in the heliosphere have reached unprecedented quiet levels. This unique minimum has been observed by the Earth–orbiting satellite, PAMELA, launched in June, 2006, from which vast sets of accurate proton and electron preliminary observations have been made available. These simultaneous measurements from PAMELA provide the ideal opportunity to conduct an in–depth study of CR modulation, in particular charge–sign dependent modulation. In utilizing this opportunity, a three–dimensional, steady–state modulation model was used to reproduce a selection of consecutive PAMELA proton and electron spectra from 2006 to 2009. Thiswas done by assuming full drifts and simplified diffusion coefficients, where the rigidity dependence and absolute value of themean free paths for protons and electrons were sequentially adjusted below 3 GV and 300 MV, respectively. Care has been taken in calculating yearly–averaged current–sheet tilt angle and magnetic field values that correspond to the PAMELA spectra. Following this study where the numerical model was used to investigate the individual effects resulting from changes in the tilt angle, diffusion coefficients, and global drifts, it was found that all these modulation processes played significant roles in contributing to the total increase in CR intensities from 2006 to 2009, as was observed by PAMELA. Furthermore, the effect that drifts has on oppositely charged particles was also evident from the difference between the peak–shaped time profiles of protons and the flatter time profiles of electrons, as is expected for an A < 0 polarity cycle. Since protons, which drift into the heliosphere along the heliospheric current–sheet, haven’t yet reached maximum intensity levels by 2008, their intensities increased notably more than electrons toward the end of 2009. The time and energy dependence of the electron to proton ratios were also studied in order to further illustrate and quantify the effect of drifts during this remarkable solar minimum period. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2012.

Beryllium-7 is a cosmogenic radionuclide produced in the atmosphere through the spallation of nitrogen and oxygen nuclei by cosmic-ray-produced neutrons and protons. It is carried in the atmosphere attached to aerosols and is deposited on land and ocean surfaces by wet and dry deposition processes. Beryllium-7 decays by electron capture to lithium-7 and has a half-life of approximately 53 days. It is a potentially useful radionuclide for studying different natural processes. This thesis presents a collection of scientific papers on the occurrence of beryllium-7 in the natural environment, particularly in the Southeast Queensland region of Australia. It shows the results of experimental measurements and discusses their implications. Overall, this thesis contributes to advancing our understanding of the distribution and behaviour of beryllium-7 in the natural environment and provides a foundation for the development of nuclear techniques for the evaluation of environmental problems.

De nombreuses observations astrophysiques indiquent l'existence de grandes quantités de masse manquante dans l'Univers, et ce de l'échelle galactique à l'échelle cosmologique. Découvrir la nature de cette masse invisible constitue le problème de la matière noire, qui apparaît comme l'un des enjeux majeurs de la physique moderne. Cette thèse s'inscrit dans le contexte de la détection indirecte de matière noire. Cette dernière serait composée de nouvelles particules élémentaires, dont les produits d'annihilation pourraient être observés dans le rayonnement cosmique. Nous étudions dans ce travail deux des canaux de recherche les plus prometteurs : les photons gamma et les anti-noyaux.Les objets astrophysiques permettant de placer les meilleures contraintes actuelles en rayons gamma sont les galaxies naines sphéroïdes (dSphs) de la Voie Lactée. La première partie de notre travail a été consacrée à contraindre les facteurs J d'annihilation de ces objets, qui quantifient l'amplitude des flux gamma attendus. Nous avons pour cela mis au point une configuration optimisée d'analyse de Jeans, pour reconstruire les profils de densité de matière noire et leurs incertitudes à l'aide des données cinématiques stellaires. Notre configuration a été obtenue à l'aide de tests systématiques sur de très nombreuses dSphs simulées, et nous l'avons appliquée à vingt-trois dSphs de la Voie Lactée. La seconde partie de notre travail a consisté à mener une recherche de noyaux d'anti-hélium dans les données collectées par l'expérience AMS-02 sur la Station Spatiale Internationale. Nous avons pour cela mis au point une classification par arbres de décision boostés, et notre analyse préliminaire a permis d'obtenir les meilleures contraintes actuelles sur les rapports anti-hélium sur hélium. / Many astrophysical observations suggest the existence of large amounts of missing mass in the Universe, from the galactic to the cosmological scale. Discovering the nature of this invisible mass forms the dark matter problem, which appears as one of the major challenges of modern physics. This thesis is established in the context of indirect detection of dark matter. The latter could consist of new elementary particles, whose annihilation products may be observed in cosmic rays. We study in this work two of the most promising research channels!: gamma-rays and anti-nuclei.The best constraints on dark matter properties from gamma-ray observations come from the dwarf spheroidal galaxies (dSphs) of the Milky Way. The first part of our work was devoted to computing the annihilation J-factors of these objects, which quantify the magnitude of the expected gamma-ray flux. We have developed an optimized Jeans analysis setup in order to reconstruct the dark matter density profiles of these objects and their associated uncertainties, using stellar kinematic data. Our optimized setup was obtained using systematic tests on numerous simulated dSphs, and we applied it to twenty-three dSphs of the Milky Way. The second part of our work was dedicated to the search for anti-helium nuclei in the cosmic ray data collected by the AMS-02 experiment on the International Space Station. We have developed a classification method using boosted decision trees, and our preliminary analysis has led to the best constraints to date on the anti-helium to helium ratio.

AMS-02 est un spectromètre magnétique conçu pour la détection du rayonnement cosmique chargé et des photons gamma. La mesure en 2013 de la fraction de positons par AMS-02 a confirmé la présence d'une composante de positons primaires, nécessitant l'existence d'une source de positons dans notre Galaxie. Cette thèse s'est exclusivement consacrée à l'étude de ce phénomène, et à la recherche de cette source de positons. La fraction de positons, le flux de positons et le flux d'électrons sont mesurés à l'aide d'une méthode de fit multidimensionnel mis au point lors de cette thèse. Une étude particulière est réservé au phénomène de confusion de charge, important pour la mesure du signe de la charge à haute énergie. La fonction de réponse instrumentale du détecteur est évaluée à l'aide de simulations Monte Carlo et est corrigée par les données réelles du détecteur. Un travail phénoménologique est effectué afin d'interpréter les résultats mesurés. L'interprétation de ces résultats en termes de composante primaire issues d'un pulsar local et du halo galactique de matière noire est effectué. Les implications et l'espace des paramètres autorisé pour chacun des modèles est explicité. Une ré-évaluation des secondaires à l'aide des nouvelles données d'AMS-02, ainsi que l'étude de l'impact de l'erreur expérimentale d'AMS-02 sur ces résultats, est exécuté. / AMS-02 is a magnetic spectrometer design for the cosmic ray and gamma ray detection. The measurement in 2013 of the positron fraction by AMS-02 confirmed the presence of a primary positron component, which means the existence of a galactic primary source of positrons. This thesis is devoted exclusively to the study of this phenomenon. The positron fraction, the positron flux, and the electron flux are measured using a method of multidimensional fit developed during this thesis. The charge confusion phenomenon, which is important at the highest energies, is investigated. The instrumental response function of the detector is evaluated using Monte Carlo simulations and is corrected using the ISS data. A phenomenological work is done to interpret the measured results. The interpretation of these results in terms of primary component from a local pulsar and dark matter halo is done. The implications and the parameter space allowed for each model is detailed. A reevaluation of secondaries with the new AMS-02 data, and the study of the impact of the experimental error of AMS-02 on these results is performed.

Près d'un siècle après leur découverte, les rayons cosmiques sont encore sujets à de nombreuses interrogations. À ultra-haute énergie (UHE), leur nature, leur origine et leur mécanisme de production restent encore inconnus malgré les avancées expérimentales. L'observatoire Pierre Auger est actuellement l'expérience incontournable pour tenter de répondre à ces questions. Dans ce contexte, l'étude et la recherche de neutrinos à UHE sont susceptibles d'apporter des informations encore manquantes au puzzle des rayons cosmiques d'ultra-haute énergie, notamment quant à leur mécanisme de production ou leur origine. C'est dans ce cadre que s'inscrit cette thèse, centrée sur la recherche de neutrinos à UHE à l'observatoire Pierre Auger et plus particulièrement sur l'étude des neutrinos arrivant sous l'horizon (i.e. à incidence rasante) et interagissant dans la croûte terrestre. Dans une première partie, le contexte phénoménologique et expérimental dans lequel s'inscrit cette thèse est introduit. Dans une seconde partie, nous présenterons tout d'abord notre étude des incertitudes systématiques sur les modèles d'interactions à UHE des neutrinos et des leptons tau à travers une analyse revisitée des neutrinos tau à incidence rasante. Cette étude s'inscrit dans le cadre de la combinaison des résultats des différents canaux de détection de l'observatoire qui a permis de poser une limite compétitive sur les flux de neutrinos à UHE, au delà de la limite de Waxman et Bahcall. Nous présenterons ensuite notre travail effectué sur les neutrinos électroniques à incidence rasante. Ces derniers engendrent, en interagissant dans la croûte terrestre, des gerbes électromagnétiques souterraines soumises à l'effet LPM (Landau, Pomeranchuk et Migdal) qui entraîne un retard de leur développement et augmente leur probabilité de détection. Une chaîne complète de simulation de ce canal a été développée afin d'évaluer la sensibilité de l'observatoire à ces évènements. Enfin, dans le cadre de propositions d'améliorations de l'observatoire en vue d'accroître ses performances à partir de 2015, nous présentons l'étude que nous avons effectuée sur l'impact d'une nouvelle électronique d'acquisition et de nouveaux modes de déclenchements sur l'efficacité de détection des neutrinos à incidence rasante par les stations du réseau au sol. / Nearly one century after their discovery, cosmic rays are still subject to many questions. In particular at ultra-high energy (UHE) where their nature, origin and production mechanism are still unknown despite numerous experimental advances. The Pierre Auger observatory is currently the key experiment to try to answer these questions. In this context, the search for UHE neutrinos remains a major challenge for astroparticle physics. Their study is likely to bring informations that are still missing to the ultra-high energy cosmic ray puzzle regarding their origin and production mechanism. This thesis focuses on the search for UHE neutrinos at the Pierre Auger observatory and particularly on neutrinos arriving below the horizon (i.e. earth skimming) and interacting in the earth crust. In a first part, the phenomenological and experimental context is introduced. In a second part, we first present our study of systematic uncertainies on interactions models of UHE neutrinos and tau lepton through a revisited analysis of earth skimming tau neutrinos in the context of the combination of the results of the different observatory's detection channels. This combination allowed to put a competitive limit on the UHE neutrinos flux, beyond the Waxman and Bachal limit. We will then show our work on earth skimming electron neutrinos. They produce, by interacting in the earth crust, underground electromagnetic showers subject to the LPM (Landau, Pomeranchuk and Migdal) effet which causes a delay in their development and increaase their detection probability. A complete simulation chain of this channel was developed in order to estimate the sensitivity of the observatory to such events. Finally, in the context of proposals to upgrade the observatory in order to improve its performance beyond 2015, we present the study we have performed about the impact of a new acquisition electronic and new triggers on the earth skimming neutrinos detection efficiency by the stations of the ground array.

Orientador: Prof. Dr. Marcelo Augusto Leigui de Oliveira / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2016. / We present in this work studies on ultra-high energy cosmic rays using the air- uorescence detection technique. The research main objective consists in event reconstructions from a fluorescence telescope, such that a simulation code has been developed taking into account the physical processes involved in the generation and the propagation of uorescence photons from an extensive air shower to a telescope. The secondary particles of air showers has been previously obtained using CORSIKA code for dierent primary energies and compositions. Furthermore, the photon generation has been calculated using Bethe and Bloch equation for the energy loss of electrons and positrons in air and the uorescence yield parameterized with air conditions at given altitudes. The attenuation of photons towards the telescope has been calculated for Rayleigh and Mie scatterings. With the developed simulation, it was possible to study the dependence of the shower maximum depth in the atmosphere, considering dierent experimental congurations for the telescopes used in the Pierre Auger Observatory, Telescope Array and MonRAt. Finally, the reconstruction of the geometric parameters of cosmic rays has been performed by the determination of the arrival directions and the angular reconstruction limits.

La formation et l'activité des objets compacts, tels que Trous Noirs ou étoiles à Neutrons, s'accompagne couramment d'éjection de matière ionisée sous forme de jets à la vitesse proche de celle de la lumière (vitesses relativistes). Se propageant dans le milieu environnant, par exemple Milieu Interstellaire, ces jets conduisent inéluctablement à la formation d'ondes de choc relativistes. Une forte turbulence magnétique et une population d'électrons accélérés sont requises afin de tenir compte de l'émission radiative non-thermique de ces chocs. L'approche naturelle de ce problème, décrivant de manière auto-consistante la structure du choc non-collisionnel, est celle de la physique cinétique des plasmas en régime relativiste. L'aspect essentiel de cette approche est l'étude du précurseur du choc, sous forme d'un faisceau de protons très énergétiques. Un ensemble d'instabilites plasma y prend lieu et dissipe l'energie du choc sous forme de micro-turbulence électromagnétique, électrons chauffés et particules accélérées. Ce cadre conceptuel emmène à reconsidérer le processus de transport de particules charges autour du choc. Deux études indépendantes, effectuées pendant la thèse, montrent que les lois de diffusion en aval et amont du choc se mettent sous une forme concise, en loi de puissance en fonction de l'énergie des particules et de l'intensité de la micro-turbulence magnétique. Les lois de diffusion, dérivées à l'aide des simulations Monte-Carlo et analytiquement, chiffrent l'énergie maximale des protons accélérés au choc à 10^15 eV, si le facteur de Lorentz du choc est très grand devant 1. Cette limite se situe loin de l'énergie maximale des Rayons Cosmique et rend les chocs relativistes comme accélérateurs de particules inefficaces aux énergies les plus extrêmes. Le rayonnement, issu de l'accélération des électrons, atteint plusieurs GeV et corrobore l'idée que les chocs externes des Sursauts Gamma peuvent émettre à de telles énergies. L'approche alternative de l'étude des chocs, simulations Particle-In-Cell, m'as permis d'étudier la formation, structuration et évolution des chocs modérément relativistes dans une géométrie spatiale 1D. L'auto-reformation du front d'un choc perpendiculaire, connue dans le régime non-relativiste, persiste dans le régime moyennement relativiste et exhibe un front de choc non-stationnaire. A magnétisation basse, les électrons sont préchauffés dans le pied du choc par l'instabilité de Buneman entre protons réfléchis et électrons incidents, mais leur température en aval du choc reste plus faible que celle des protons. A magnétisation croissante, l'instabilité Maser Synchrotron devient essentielle dans la structuration du front de choc, avec émission d'un fort précurseur électromagnétique a partir du front de choc. Dans ce cas les électrons se mettent en équipartition avec les protons. Ces simulations 1D ne montrent pas d'évidence d'accélération des particules et des simulations 2D (3D) sont nécessaires. / The formation and activity of compact objects such as Black Holes and Neutron Stars results in the ejection of ionized matter in the form of jets with velocities close to $c$ (relativistic). The interaction of such powerful jets with the external medium forms shocks, eventually relativistic.A strong self-g???enerated magnetic micto-turbulence and a population of accelerated electron are required to explain the observed non-thermal radiation of these shocks. A natural approach to the study of the structure of a non-collisionnal shock involves kinetic treatement of plasma processes in the relativistic limit. This approach is adopted in the present thesis.Consequently, charged particle transport laws need to be studied carefully taking to acount self-consistent magnetic micro-turbulence at the shock. Two different studies of particle transport at each side of the shock (downstream and upstream) show that the diffusion laws take a concise form as a power law in energy ($D \propto E^2$) and the micro-turbulence strength. Both Monte-Carlo simulations and analytic studies are in agreement and, if the shock Lorentz factor is much greater than 1, it is found that the maximum energy of accelerated protons is $10^{15}$eV. A physical mechanism is also provided to explain how electrons attain the equipartition with protons at the shock. Finally, the radiation from accelerated electrons at the shock can reach several GeV in a synchrotron-like spectrum.In the second part of the thesis, I used 1D3V PIC simulations to study mildly relativistic shocks structure and their time evolution. The prependicular shock front self-reformation, well-known in non-relativistic limit, persists at mildly relativistic speeds. At low magnetization ($\sigma \ll 10^{-2}$), electrons are pre-heated in the shock precursor by the Buneman instability between reflected ions and incident electrons. At higher magnetizations ions form a coherent cyclotron loop at the front and the Maser Synchrotron Instability is essential for the shock structure by emitting a strong electromagnetic precursor, responsible for electrons heating up to equipartition with protons. No particle acceleration is seen in these 1D3V simulations.