Submitted by Biblioteca do Instituto de Física (bif@ndc.uff.br) on 2017-02-20T18:40:57Z No. of bitstreams: 1 Tese_Jaime_Souza_de_Oliveira_julho_2016.pdf: 15333015 bytes, checksum: 0553ac5f9d75c22b81dccf4042511eb6 (MD5) / Made available in DSpace on 2017-02-20T18:40:57Z (GMT). No. of bitstreams: 1 Tese_Jaime_Souza_de_Oliveira_julho_2016.pdf: 15333015 bytes, checksum: 0553ac5f9d75c22b81dccf4042511eb6 (MD5) / Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Conselho Nacional de Desenvolvimento Científico e Tecnológico / O início deste estudo de doutorado, em 2012, coincidiu com a celebração do primeiro centenário da descoberta da radiação cósmica. Embora nosso conhecimento sobre estas partículas tenha aumentando consideravelmente ao longo do último século, ainda há muitas questões que necessitam ser elucidadas, principalmente para aquelas com energias acima de 1018 eV, denominadas raios cósmicos de energia ultra alta. A razão para isso é que o fluxo destas partículas é extremamente pequeno, indo de uma partícula por km2 por ano, na faixa de energia de 1018 eV, a uma partícula por km2 por século, em energias ainda mais elevadas. Para compensar este baixo fluxo de partículas, foram construídos observatórios enormes nas últimas décadas, sendo o maior deles, o Observatório Pierre Auger, foco dos estudos realizados nesta tese. Embora o Observatório Auger, em operação desde 2004, venha realizando descobertas significativas com respeito aos raios cósmicos ultra-energéticos, ainda não se sabe, de maneira indubitável, quais são suas fontes, composição química, mecanismos de aceleração e propagação. Em especial, o estudo de anisotropias nas direções de chegada dos raios cósmicos à Terra é de fundamental importância para o entendimento destas questões. Assim, a principal contribuição desta tese trata de um estudo em multirresolução de anisotropias no fluxo dos raios cósmicos detectados no Observatório Auger, com energias acima de 4×1018 eV. Para isso, medidas do espectro de potência angular foram realizadas sob nossa responsabilidade, enquanto que uma análise complementar, utilizando needlets, foi empregada por um grupo de físicos da Universidade de Aachen, Alemanha. Ainda no contexto de anisotropia, destacamos um outro estudo realizado nesta tese, no qual mostramos não haver inconsistência entre resultados obtidos em duas análises distintas, uma usando somente dados da Colaboração Auger e outra usando também dados da Colaboração Telescope Array. Adicionalmente, também descrevemos um estudo relacionado ao aprimoramento dos detectores de superfície do Observatório Pierre Auger, no qual mostramos que os tanques de radiação Cherenkov podem ser calibrados e terem sua performance avaliada com a colocação de um detector de múons sob eles. / In 2012, the beginning of this Ph.D study coincided with the celebration of the first centenary of the cosmic radiation discovery. Although our knowledge these particles has increased considerably over the last century, there are still many issues to be clarified, particularly for those with energies above 1018 eV, called ultra high energy cosmic rays. The reason for this is that the flux of these particles is extremely low, from one particle per km2 per year at 1018 eV to one particle per km2 per century at even higher energies. In order to compensate this very low flux of particles, large observatories were built in recent decades. The largest one is the Pierre Auger Observatory, focus of the studies performed in this thesis. Although the Auger Observatory, in operation since 2004, has been reporting breakthroughs with regard to ultra-high energy cosmic rays, there is still no consensus related to their sources, chemical composition, acceleration and propagation mechanisms. Particularly, the study of anisotropies in the cosmic ray arrival directions is of fundamental importance for the understanding of these issues. Thus, the main contribution of this thesis is a multi-resolution anisotropy study of the cosmic ray flux detected in the Auger Observatory with energies above 4 × 1018 eV. To this goal, the angular power spectrum were performed under our responsibility, while one additional analysis, using needlets, was used by a group from Aachen University, Germany. Still within the context of anisotropy, we reported another study of this thesis, in which it was shown that there is no inconsistency between results obtained in two different analysis, one using only data obtained by the Auger Collaboration and another one using events from Auger and Telescope Array collaborations. In addition, we also described a different study related to the upgrade of the surface detectors of the Pierre Auger Observatory, in which we showed that the water Cherenkov tanks can be studied and calibrated by placing a muon detector under them.

La description actuelle des interactions fondamentales repose sur deux théories ayant le statut de modèle standard. Les interactions électromagnétiques et nucléaires sont décrites à un niveau quantique par le Modèle Standard de la physique des particules, alliant théories de jauge et brisures spontanées de symétrie par le mécanisme de Higgs. À l'opposé, l'interaction gravitationnelle est décrite par la relativité générale,basée sur une description dynamique de l'espace-temps dans un cadre classique.Bien que ces deux modèles soient vérifiés avec une grande précision dansle système solaire, ils sont affligés d’un certain nombre de problèmes théoriques et manquent de force prédictive aussi bien à l'échelle de Planck qu’à l'échelle cosmologique ;ils ne sont par conséquent plus perçus comme fondamentaux. La cosmologie, dont la phénoménologie fait apparaitre ces deux échelles extrêmes, apparaît alors comme un laboratoire privilégié pour tester les théories au delà de ces modèles standards.La première partie de cette thèse concerne l'étude des cordes cosmiques, défauts topologiques se formant lors de la brisure spontanée de théories de grande unification dans l'univers primordial.J’y montre notamment comment étudier ces défauts en prenant en compte la structure complète des théories de physique des particules dont ils sont issus, ce qui représente une avancée importante par rapport à la description courante en termes de modèles ”jouets”très simplifiés. La deuxième partie de cette thèse consiste en la construction et l'étude de différentes théories de gravité modifiée liées au modèle de Galiléon, un modèle tentant notamment d'expliquer la phénoménologie liée à l'énergie noire. / The current description of fundamental interactions is based on two theories with the status of standard models. The electromagnetic and nuclear interactions are described at a quantum level by the Standard Model of particle physics, using tools like gauge theories and spontaneous symmetry breaking by the Higgs mechanism. The gravitational interaction is described on the other hand by general relativity, based on a dynamical description of space-time at a classical level.Although these models are verified to high precision in the solar system experiments, they suffer from several theoretical weaknesses and a lack of predictive power at the Planck scale as well as at cosmological scales; they are thus not viewed anymore as fundamental theories. As its phenomenology involves both these extreme scales, cosmology is then a good laboratory to probe theories going beyond these standard models.The first part of this thesis focus on cosmic strings, topological defects forming during the spontaneous symmetry breaking of grand unified theories in the early universe. I show especially how to study these defects while taking into account the complete structure of the particles physics models leading to their formation, going beyond the standard descriptions in terms of simplified toy-models. The second part is devoted to the construction and the examination of different theories of modified gravity related to the Galileon model, a model which tries in particular to explain the dark energy phenomenology.

Software effort estimation still remains a challenging and debatable research area. Most of the software effort estimation models take software size as the base input. Among the others, Constructive Cost Model (COCOMO II) is a widely known effort estimation model. It uses Source Lines of Code (SLOC) as the software size to estimate effort. However, many problems arise while using SLOC as a size measure due to its late availability in the software life cycle. Therefore, a lot of research has been going on to identify the nature of relationship between software functional size and effort since functional size can be measured very early when the functional user requirements are available. There are many other project related factors that were found to be affecting the effort estimation based on software size. Application Type, Programming Language, Development Type are some of them. This thesis aims to investigate the nature of relationship between software size and development effort. It explains known effort estimation models and gives an understanding about the Function Point and Functional Size Measurement (FSM) method. Factors, affecting relationship between software size and development effort, are also identified. In the end, an effort estimation model is developed after statistical analyses. We present the results of an empirical study which we conducted to investigate the significance of different project related factors on the relationship between functional size and effort. We used the projects data in the International Software Benchmarking Standards Group (ISBSG) dataset. We selected the projects which were measured by utilizing the Common Software Measurement International Consortium (COSMIC) Function Points. For statistical analyses, we performed step wise Analysis of Variance (ANOVA) and Analysis of Co-Variance (ANCOVA) techniques to build the multi variable models. We also performed Multiple Regression Analysis to formalize the relation. / Software effort estimation still remains a challenging and debatable research area. Most of the software effort estimation models take software size as the base input. Among the others, Constructive Cost Model (COCOMO II) is a widely known effort estimation model. It uses Source Lines of Code (SLOC) as the software size to estimate effort. However, many problems arise while using SLOC as a size measure due to its late availability in the software life cycle. Therefore, a lot of research has been going on to identify the nature of relationship between software functional size and effort since functional size can be measured very early when the functional user requirements are available. There are many other project related factors that were found to be affecting the effort estimation based on software size. Application Type, Programming Language, Development Type are some of them. This thesis aims to investigate the nature of relationship between software size and development effort. It explains known effort estimation models and gives an understanding about the Function Point and Functional Size Measurement (FSM) method. Factors, affecting relationship between software size and development effort, are also identified. In the end, an effort estimation model is developed after statistical analyses. We present the results of an empirical study which we conducted to investigate the significance of different project related factors on the relationship between functional size and effort. We used the projects data in the International Software Benchmarking Standards Group (ISBSG) dataset. We selected the projects which were measured by utilizing the Common Software Measurement International Consortium (COSMIC) Function Points. For statistical analyses, we performed step wise Analysis of Variance (ANOVA) and Analysis of Co-Variance (ANCOVA) techniques to build the multi variable models. We also performed Multiple Regression Analysis to formalize the relation. / +46-(0)-739763245

In this licentiate thesis, I report a search for GeV γ rays towards the location of Galaxy clusters. I mainly discuss the results of a search for cosmic-ray (CR) induced γ-ray emission but also briefly elaborate on a related study, searching for Dark Matter (DM)-induced γ-ray emission from Galaxy clusters. In addition, I provide a detailed discussion on the analysis tools that were used and discuss some additional tests that are not included in the papers this licentiate thesis is based on. In a comprehensive search almost covering the entire sky, we find no statistically significant evidence for either DM or CR induced γ rays from galaxy clusters. Thus we report upper limits on CR quantities that exclude emission scenarios in which the maximum hadronic injection efficiency is larger than 21% and associated limits on the maximum CR-to-thermal pressure ratio, <XCR>. In addition, we update previous flux upper limits given a new set of modeling and taking the source extension into account. For a DM masses below 100 GeV, we exclude annihilation cross sections above ∼ 10−24 cm3 s−1 into bb. For decaying DM, we exclude decay times lower than 1027 s over the mass range of 20 GeV– 2 TeV.

Identifying what makes up the Dark Matter is a long-standing problem to which the abundance of gravitational and cosmological evidence fails to answer. Indirect detection techniques have the aim to unveil the nature of Dark Matter by catching and identifying the products of potential decays and/or annihilations. The work exposed in this thesis is in line with this strategy and has for common thread the quest for line(-like) features in the extraterrestrial fluxes of gamma-rays and neutrinos. The motivation behind this specific interest is that, due to the absence of astrophysical counterparts beyond the GeV scale, these features constitute the ultimate probes (also called “smoking guns”) of the existence of Dark Matter.The thesis is organized in three Parts, the first of which is an introduction to the different facets of the Dark Matter conundrum and why it is not a trivial issue. The works involving gamma-ray line considerations are gathered in Part II, and those exclusively focusing on neutrino lines in Part III.Part II focuses on the effective field theory of Dark Matter decay, first in the context of millicharged particles decaying to gamma-ray lines, and then in the context of (neutral and millicharged) Dark Matter decays involving the simultaneous emission of gamma-ray and neutrino lines. In both cases, the simultaneous emission of cosmic rays is unavoidable and the decays are constrained in a multi-messenger fashion. The complementarity of the results obtained is used to derive model-independent constraints on the Dark Matter lifetime, and shows the possibility to exclude or distinguishsome specific scenarios on the basis of an explicit experimental conjecture.After an introduction to the neutrino detection principles and to the operation of the IceCube detector, Part III focuses on two careful searches for spectral features in the neutrino spectrum. The main goal behind these analyses, conducted in two different regions of the energy spectrum but using the same likelihood ratio procedure, is to popularize dedicated energy distribution studies by showing their ability to reach sensitivity levels comparable to—sometimes even going beyond—those obtained with angular distribution studies or even in the context of gamma-ray line searches. / Option Physique du Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Les missions modernes permettent d’accéder à des mesures de qualité pour les grandes structures, en échantillonnant la distribution de galaxies en détail jusque dans les régions les moins denses, les vides. Toutefois, nous observons les vides dans l’espace des redshift, ce qui limite notre connaissance de ces structures. Afin d’utiliser les vides en tant qu’outils cosmologiques de précision, il est fondamental d’obtenir leur forme dans l’espace réel. Dans cette thèse nous présentons un algorithme non-paramétrique permettant de reconstruire les profils de densité sphérique des vides empilés dans l’espace réel, sans assomption pour les distorsions en redshift. Nous obtenons donc les premiers profils de densité des vides empilés dans l’espace réel, à travers lesquels nous étudions la compensation de masse et calculons les profils de vitesses particulières des vides, se basant sur la théorie linéaire et le modèle cosmologique. Nous discutons l’utilisation des profils pour contraindre indépendamment les vitesses. Avec des catalogues simulés de galaxies, nous analysons l’effet des vitesses particulières sur les propriétés physiques des vides. Enfin nous calculons une prédiction du nombre de vides que fournira la future mission Euclid et des contraintes que ce nombre de vides donnera sur les paramètres cosmologiques (grâce au formalisme de Fisher). Les profils de densité de vides dans l’espace réel peuvent être utilisés pour tester les modèles cosmologiques (à travers l’étude de l’effet des vitesses particulières et l’amélioration du test de Alcock-Paczynski); l’étude des vides promet donc d’apporter des informations indépendantes pour éclaircir le mystère de l’énergie obscure. / Modern surveys allow us to access to high quality measurements, by sampling the galaxy distribution in detail also in the emptier regions, voids. When we observe cosmic voids, however, we observe them in redshift-space: their real shape remains inaccessible to us, thus limiting our knowledge about such structures. To employ voids as a precision tool for Cosmology, it is fundamental to obtain their real-space shape. This thesis presents a model-independent non-parametric algorithm to reconstruct the spherical density profiles of stacked voids in real space, without assumptions about redshift distortions. With this algorithm, we obtain the first ever real-space density profiles of stacked voids. With the profiles we study the mass compensation and obtain a theoretical prediction for the velocity profiles of voids based on linear theory and assuming cosmological parameters. In parallel, we discuss the use of the real-space profiles to obtain model-independent information about the peculiar velocity profiles of voids. Also, using mock catalogues, we analyse the effect of peculiar velocities on void properties and discuss it in the framework of current and future surveys. Finally we calculate a forecast for void abundances with the future Euclid mission and obtain, using the Fisher matrix formalism, a prediction for the constraints that void abundances will set on cosmological parameters. The real-space profiles of voids can be used to test cosmological models (through the understanding of peculiar velocities effects and the improvement of the Alcock-Paczynski test); and void abundances promise to bring independent information and to shed light on the mystery of dark energy.

The study of continuum sky background spectrum at low radio frequencies has achieved specific importance in present day observational cosmology . At these low frequencies the sky continuum is contributed by the extragalactic radio sources together with the synchrotron emission of the Milky Way as well as CMB. Following the recombination, the energy exchange between the primordial neutral hydrogen and CMB photons, during its propagation through the ”Dark ages” as well as the ”cosmic dawn” resulted in absorption and emission features in CMB spectrum which evolved with the evolution of the HI over cosmic time. Due to cosmological expansion of the Universe such spectral signatures of cosmological origin is now redshifted to low radio wavelengths. Although the peak to peak amplitudes of the same are smaller by orders of magnitude than the total galactic and extragalactic contribution at these frequencies the later is expected to be smooth over the scales of few hundred MHz. Hence, except for the extreme cases where the time scale over which such radiative transfer interaction occurred is very long and therefore the spectral fluctuations are spread over a large range of frequencies, these cosmological radiation signatures should be detectable at meter wavelengths. The duration and frequency at which such spectral signatures may occur can give constraints on the physical processes that governed the process of such energy exchange at a very early time, the history of evolution of the gas and the nature and evolution of sources of first light in the Universe. Measurements of the absolute brightness of the continuum background at meter wavelengths and detection of the spatial and spectral variations can therefore be an important probe of cosmology. In addition, measurements to date suggest that the radio background that is of extragalactic origin consists of CMB plus a power-law spectrum and has a brightness temperature of (1.2 ± 0.09) × (ν/1 GHz)−2.60±0.04 K. Surprisingly, the sky brightness corresponding to discrete radio sources detected in the deepest surveys to date account for only a fraction of the extragalactic radio background, even after excluding the CMB. Improved measurements of the radio background and, in particular, the spectrum at long wavelengths where errors are relatively larger, are important in estimating the spectrum of the unexplained part and thereby constraining the sources of this cosmic radiation. The wideband measurements at meter wavelengths pose limit on the accuracy of such measurements where the errors are relatively large. The instrument systematics, which are frequency dependent, in interaction with the sky signal may result in an incorrect estimate of the absolute sky brightness as well as may give rise to spectral features which may confuse with the true cosmological signatures in the foreground. A strategic system design with the aim of minimizing the systematics and characterization of the system non-ideal behavior can lead to the measurement accuracy with which the cosmological signatures could be detected along with the absolute measurement of the foreground. The aim of the work that constitute this thesis is precision measurement of the continuum radio emission at long wavelengths and detect the signature from the epoch of reionization in the background spectrum. A single element radio telescope system has been designed and built which is capable of useful measurement of spectral signatures of the EoR in the radio background. SARAS deployed in the Gauribidanur Observatory, about 80 km north of Bangalore in India. The design, calibration method and observation strategies developed are novel and unique, and relevant for any wideband measurements. The content of this thesis is outlined below. The Chapter 1 briefly introduces to the 21 cm cosmology. The neutral hydrogen as an cosmological probe is discussed first. The redshifted 21 cm signal and its possible use to probe the early Universe is discussed in detail. The chapter also gives a description of the redshifted 21 cm background and the EoR global signature as well as the 21 cm power spectrum. Finally an account of the recent and future experiments for detection of the global EoR signature and the EoR power spectrum are given. In the light of the science introduced in this chapter, the major aim and the work of the thesis is also summarised. In Chapter 2 the design philosophy of the SARAS spectrometer is illustrated. The basic elements of the system, the antenna, analog and the digital receiver have been described in detail. The complete configuration and the complex performance of the integrated system are detailed. For an ideal performance of such a wideband system the calibration strategies are considered and measurement equations are derived. Chapter3 addresses the most important issues of systematic effect for this wideband continuum measurement. The designed system performance deviates from its ideal due to non-idealities. The non-ideal behaviour of the real systems that are the limiting factors for a precision wideband measurement at low frequencies are thoroughly investigated. The effects of single and multiple reflections that occurs due to impedance mismatch internal to the system and results in spurious response in the measured data are considered. Within the limits of the known systematics, the system has been argued to qualify to be able to measure the EoR spectral signature in the background spectrum. Chapter 4 gives the details of the SARAS observation and description of the measurement that has been done by the SARAS spectrometer from the Gouribidanur Radio Observatory . The detailed understanding of the systematics led to the two strategic observation modes; EoR mode and RB mode, which are also discussed in this chapter. Next, the absolute calibration of the SARAS spectrometer is described following which the interference rejection algorithms, purpose developed for rejection of RFI from the SARAS data are outlined. The measured data is calibrated and the additional calibration product is derived. The data set is then modelled by modelling the sky noise and the systematic effects. In Chapter 5 the methodology of the SARAS data analysis is illustrated along with step by step analysis of the observation made in the RB mode. The model that is derived in chapter 4 is fitted to the measurements and the parameters are estimated by minimising the merit function Chi-square. The minimisation followed the downhill simplex algorithm which is outlined in this chapter. The data analysis strategy relied on the derivation of the initial values of the parameters from the measured data. The data has been fitted in hierarchy and initial guesses for subset of parameters are derived from each step of hierarchical modelling. This method of analysis is strategic and discussed in detail in this chapter. The statistical and systematic error of measurement are discussed next. Finally, the posterior probability distribution of the parameters are calculated by uniformly sampling the parameter space around the best fit values and calculating the Chi-square and the likelihood functions of the parameters. Mariginalizing the computed posterior probability distribution over the system parameters, the error on estimated sky parameter or the confidence region of the sky parameter is estimated. Chapter 6 presents the analysis identical to that presented in the Chapter 5 for the data acquired in the second observing mode, the EoR mode is presented. In this section the detection ability and the limitations of the SARAS observations, made from the Gouribidanur Radio observatory, for a useful detection of the EoR spectral signature is considered. Chapter 7 described a concept of system bandpass calibration using the time domain information that could be obtained from the voltage samples before computing the power spectrum. In the Chapter 3, the spurious periodic correlation, generated due to the internal reflections of the noise voltages is discussed in detail. If a short pulse is injected into the system via the antenna, due to internal reflections, the primary pulse in the output voltage samples would be followed by a series of delayed pulses each of which is generated by subsequent reflections internal to the system. Inspection of such pulses in the time domain could potentially provide with accurate bandpass calibration. A digital hardware is programmed and a nano second pulse generator-accumulator system is built. The performance of this system and table top demonstration of this bandpass calibration concept is presented in this chapter. This pulse injection system is used in a proposed calibration experiment in the Parkes radio telescope. The initial result of the experiment is presented in this chapter. In Chapter 8 the work carried out for this thesis is summarised. The end to end task of carrying out the background measurement by purpose building a single element radio telescope, observing with it and analysis of the data has led to a successful measurement of the background spectrum with an accuracy > 1%. The detailed understanding of the problems associated with the precision measurements and development of the measurement techniques that can overcome such problems has led to significant progress towards a successful detection of the EoR signatures. Some aspects and ideas which are understood to be essentials for such an experiment yet unexplored here due to limited time are listed in this section and the future prospcts of this work is also discussed.

Le rayonnement fossile, ou CMB, est un sujet d’étude clé pour la cosmologie car il indique l’état de l’univers à une époque primordiale. Le CMB est observable dans le ciel dans la bande de fréquences des micro-ondes. Cependant, il existe des processus astrophysiques, les avant-plans, qui émettent dans les micro-ondes, et rendent indispensable le traitement des données avec des méthodes de séparation de composantes. J'utilisé la méthode aveugle SMICA pour obtenir une estimation directe du spectre de puissance angulaire du CMB. La détermination des petites échelles de ce spectre est limité par les avant-plans comme les galaxies lointaines, et par le biais du bruit. Dans cette analyse, ces deux limitations sont abordées. En ajoutant des hypothèses sur la physique des galaxies lointaines, il est possible de guider l’algorithme pour estimer leur loi d'émission. Un spectre de puissance angulaire obtenu d'une carte du ciel a un biais dû au bruit à petites échelles. Toutefois, les spectres obtenus en croisant différentes cartes n'ont pas ce biais. J'ai donc adapté la méthode SMICA pour qu'elle n'utilise que ces derniers, diminuant l'incertitude due au bruit dans l'estimation du CMB. Cette méthode a été étudiée sur des nombreuses simulations et sur les données Planck 2015, afin d'estimer des paramètres cosmologiques. Les résultats montrent que la contamination résiduelle des avant-plans présente dans le spectre CMB, même si fortement réduite, peut introduire des biais dans l'estimation des paramètres si la forme des résiduels n'est pas bien connue. Dans cette thèse, je montre les résultats obtenus en étudiant un modèle de gravité modifiée. / The Planck satellite observed the whole sky at various frequencies in the microwave range. These data are of high value to cosmology, since they help understanding the primordial universe through the observation of the cosmic microwave background (CMB) signal. To extract the CMB information, astrophysical foreground emissions need to be removed via component separation techniques. In this work I use the blind component separation method SMICA to estimate the CMB angular power spectrum with the aim of using it for the estimation of cosmological parameters. In order to do so, small scales limitations as the residual contamination of unresolved point sources and the noise need to be addressed. In particular, the point sources are modelled as two independent populations with a flat angular power spectrum: by adding this information, the SMICA method is able to recover the joint emission law of point sources. Auto-spectra deriving from one sky map have a noise bias at small scales, while cross-spectra show no such bias. This is particularly true in the case of cross-spectra between data-splits, corresponding to sky maps with the same astrophysical content but different noise properties. I thus adapt SMICA to use data-split cross-spectra only. The obtained CMB spectra from simulations and Planck 2015 data are used to estimate cosmological parameters. Results show that this estimation can be biased if the shape of the (weak) foreground residuals in the angular power spectrum is not well known. In the end, I also present results of the study of a Modified Gravity model called Induced Gravity.

Cette thèse de création porte sur les nouveaux enjeux de pesanteur etde légèreté revendiqués par un certain nombre d’artistes contemporains.Nous vivons dans un monde de plus en plus pesant et pourtant les artistesexplorent des moyens de s’extraire de cette gravité pour atteindreune apesanteur théorique. Car l’apesanteur telle que nous nous la représentonsn’existe pas en terme de physique : il s’agit d’un phénomène dechute libre qui crée l’impression de flottement. J’interroge donc la notiond’(a)pesanteur, qui prend en considération cette dialectique de l’envol etde la chute, au sein de nombreuses oeuvres, principalement sculpturales. Jequestionne ma pratique de la sculpture, de l’installation et du dessin à traversle prisme de l’(a)pesanteur, qui construit un véritable rapport aumonde et à l’acte de création. J’utilise les propriétés intrinsèques du matériauafin de générer des sensations de poids ou de légèreté. J’interrogeégalement l’acte de suspendre une oeuvre dans l’espace d’exposition: lasuspension serait-elle aujourd’hui devenue le nouveau socle de la sculpture? De l’espace d’exposition à l’Espace cosmique, l’oeuvre d’art est, depuisla conquête spatiale, de plus en plus présente hors des frontières terrestres.Elle est créée dans l’Espace ou pour l’Espace : l’Espace cosmique serait-il devenu le nouveau lieu de l’art ?A travers les figures de la chute,de l’envol,du suspens,de l’imaginaire spatial,et jusqu’aux figures de l’invisible, l’(a)pesanteur tisse un véritable filrouge à travers la création contemporaine. / This creative thesis is about the new challenges of weightlessness andlightness faced by a number of contemporary artists.We are living in a increasinglyheavy world, yet artists are exploring ways to escape this gravityto reach a theoretical weightlessness. Because the way to display weightlessnessdoesn’t exist in terms of physics: it’s the phenomenon of free-fallingwhich creates this feeling of floating. So I seek to test theweight(less)ness concept, which explores this float and fall dialectic in numerousworks, mainly sculptural. I’m questioning my own practice ofsculpture, installation and drawing, through the prism of weight(less)ness,which builds an actual connection to the world and to the act of creation.I’m using the intrinsic property of the material to generate feelings ofweight or lightness. I’m also questioning the act of hanging a work in theexhibition space : nowadays, has suspension become the new pedestal of asculpture ? From the exhibition space to cosmic Space, artwork increasinglygains presence beyond earth’s boundaries, ever since the conquest ofspace. It’s created in Space and for Space : has cosmic Space become thenew place for art? Through figures of falling, of flight, of suspension, ofimaginary spaces, and even figures of invisibility, weight(less)ness builds averitable guiding light through contemporary creation.

Abstract The work describes the design, construction and commissioning of the underground cosmic-ray experiment Experiment with MultiMuon Array (EMMA). The experiment is built into the Pyhäsalmi mine, in the town of Pyhäjärvi, Finland. The aim of EMMA is to determine the elemental composition of cosmic rays at an energy region around 4 PeV, the energy region called the ’knee’ region. This is achieved by measuring the lateral density distribution of high-energy muons originating from Extensive Air Showers (EAS). The design calculations for the EMMA experiment, which are based on the use of the parametrization of the lateral density distribution of muons, the method of shower reconstruction, and the energy and composition indicators, are presented. A strategy for reconstructing the composition of the cosmic rays is presented and it demonstrates the potential of applying unfolding techniques to the EMMA data. The effect of an array extension on the performance of EMMA is studied. The hardware used in the EMMA experiment is presented starting with an overview of the array and its detector stations. The EMMA array employs three different particle detectors, for which the main technical properties are given, and their use in the EMMA array is presented. A description of the infrastructure of the experiment is given and the rock overburden at the EMMA site at the depth of 80 metres is documented. The work contains the latest analysis of EAS data recorded by the tracking detectors of the experiment, which demonstrates that the experiment is taking data as planned and that the data are according to EAS physics expectations. Methods for event selection and tracking efficiency correction are presented, after which the analysis results of measured track multiplicity spectra are given. The shape of the recorded multiplicity spectrum indicates that the simplest model of a knee-like spectrum with a pure proton composition can not explain the data and that further analysis of the spectrum is required.