This dissertation seeks to describe advancements made in computational methods for multi-messenger astrophysics (MMA) using gravitational waves GW and neutrinos during Advanced LIGO (aLIGO)’s first through third observing runs (O1-O3) and, looking forward, to describe novel computational techniques suited to the challenges of both the burgeoning MMA field and high-performance computing as a whole. The first two chapters provide an overview of MMA as it pertains to gravitational wave/high energy neutrino (GWHEN) searches, including a summary of expected astrophysical sources as well as GW, neutrino, and gamma-ray detectors used in their detection. These are followed in the third chapter by an in-depth discussion of LIGO’s timing system, particularly the diagnostic subsystem, describing both its role in MMA searches and the author’s contributions to the system itself. The fourth chapter provides a detailed description of the Low-Latency Algorithm for Multi-messenger Astrophysics (LLAMA), the GWHEN pipeline developed by the author and used in O2 and O3. Relevant past multi-messenger searches are described first, followed by the O2 and O3 analysis methods, the pipeline’s performance, scientific results, and finally, an in-depth account of the library’s structure and functionality. In particular, the author’s high-performance multi-order coordinates (MOC) HEALPix image analysis library, HPMOC, is described. HPMOC increases performance of HEALPix image manipulations by several orders of magnitude vs. naive single-resolution approaches while presenting a simple high-level interface and should prove useful for diverse future MMA searches. The performance improvements it provides for LLAMA are also covered. The final chapter of this dissertation builds on the approaches taken in developing HPMOC, presenting several novel methods for efficiently storing and analyzing large data sets, with applications to MMA and other data-intensive fields. A family of depth-first multi-resolution ordering of HEALPix images — DEPTH9, DEPTH19, and DEPTH40 — is defined, along with algorithms and use cases where it can improve on current approaches, including high-speed streaming calculations suitable for serverless compute or FPGAs. For performance-constrained analyses on HEALPix data (e.g. image analysis in multi-messenger search pipelines) using SIMD processors, breadth-first data structures can provide short-circuiting calculations in a data-parallel way on compressed data; a simple compression method is described with application to further improving LLAMA performance. A new storage scheme and associated algorithms for efficiently compressing and contracting tensors of varying sparsity is presented; these demuxed tensors (D-Tensors) have equivalent asymptotic time and space complexity to optimal representations of both dense and sparse matrices, and could be used as a universal drop-in replacement to reduce code complexity and developer effort while improving performance of existing non-optimized numerical code. Finally, the big bucket hash table (B-Table), a novel type of hash table making guarantees on data layout (vs. load factor), is described, along with optimizations it allows for (like hardware acceleration, online rebuilds, and hard realtime applications) that are not possible with existing hash table approaches. These innovations are presented in the hope that some will prove useful for improving future MMA searches and other data-intensive applications.

The General theory of Relativity was first introduced by Albert Einstein. There have been many attempts to unify General Relativity with the Standard Model of Physics and many of these try to do so by modifying General Relativity slightly. One way to do this is to add a mass to the graviton. Such a theory was proposed by Fierz and Pauli. However, a massive gravity theory suffers from the vDvZ discontinuty where taking the masss of the graviton to zero does not reproduce the results of General Relativity exactly. This can, to some extent, be resolved via the Vainshtein mechanism, where General Relativity can be reproduced within a certain radius from a source, called the Vainshtein radius. Another modification that can be imagined, is to add a second metric. However, doing this results in extra degrees of freedom which manifest as a Boulaware Deser ghost. The bimetric action which avoids the Boulaware Deser ghost was first introduced by Hassan and Rosen in 2011. In this theory, only one of the metrics couples to standard model matter to avoid the ghost. In this scenario, the propagating massless and massive spin-2 modes turn out to be linear combinations of the two metrics, just as in neutrino mixings. In this thesis, we review some works which investigate the oscillations between the massless and massive modes and the implications for gravitational waves. In particular we consider the bounds on the parameters of the theory based on the fact that evidence for such oscillations have not been observed by LIGO. We use a new LIGO result to extend these bounds. We also review an investigation which explores the possibility that the dark matter particle could be the massive particle of bimetric gravity. / Den allmänna relativitetsteorin introducerades först av Albert Einstein.Många har försökt förena allmän relativitetsteori med partikelfysikensstandardmodell och många av dessa försök gör detta genom att lägga tillen massa för gravitonen. En sådan teori föreslogs av Fierz och Pauli.Massiv gravitation lider dock av vDvZ-diskontinuiteten där gränsen närgravitonmassan går mot noll inte reproducerar allmän relativitetsteori.Detta kan, till viss del, lösas genom Vainshteinmekanismen, där allmänrelativitetsteori kan reproduceras inom ett visst avstånd från källan,kallat Vainshteinradien. En annan modifikation som kan komma på fråga äratt lägga till en andra metrik. Att göra detta leder dock till nyafrihetsgrader som yttrar sig som ett Boulaware-Deser-spöke. Denbimetriska verkan som undviker Boulaware-Deser-spöket introduceradesförst av Hassan och Rosen år 2011. I denna teori kopplar enbart en avmetrikerna till standardmodellen vilket gör att spöket kan undvikas. Idetta scenario visar sig det masslösa och det massivapropagationsegentillstånden vara linjärkombinationer av de tvåmetrikerna i analogi med neutrinoblandning. I detta arbete går vi igenomnågra arbete som undersöker oscillationerna mellan de två metrikerna ochimplikationerna för gravitationsvågor. Speciellt kommer vi att betraktade begränsningar som finns på teoriparametrarna baserat på det faktumatt LIGO inte observerat några bevis för sådana oscillationer. Vianvänder också nya LIGO-resultat för att utöka dessa begränsningar. Vidiskutera också möjligheten att mörk materia skulle kunna bestå av denmassiva gravitonen i bimetrisk gravitation.

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L’objectif de la thèse est de développer une nouvelle technique d’optique adaptive pour les interferomètres gravitationels avancés, basée sur un nouveau type de miroir pour le faisceau d’injection de l’interferomètre. Le miroir déformable, basé sur une actuation thermique, doit etre un outil compatible ultra-vide, qui fonctionne sans bruit électronique ou mécanique, bon marché et permettre la correction des modes d’ordre supérieurs afin d’améliorer le matching des faisceaux de haute puissance dans les cavités laser du détecteur sous ultra-vide. Un montage experimental de caractérisation du miroir déformable a été mis en place afin d’effectuer les tests de validation du premier prototype sous air. L’élaboration d’une procédure de caractérisation des propriétés du miroir et d’une boucle de controle a permis de développer une approche efficace pour déterminer les possibilités et les limites du miroir. Nous avons ainsi pu faire la démonstration de sa capacite a corriger les aberrations de phase d’un faisceau laser infrarouge a différentes fréquences spatiales. Nous avons également démontré que le miroir vérifie les performances de stabilité, de reproductibilité et de linearité attendues. Nous avons ensuite validé l’amélioration du mode matching d’un faisceau laser sur une cavité de réference par le miroir thermiquement déformable / In this thesis we develop a new technique of adaptive optics for the Advanced Gravitational Interferometers, based on a new type of deformable mirror for the injection beam of the interferometer. This deformable mirror, based on a thermal actuation, has to be a high vacuum compatible and low-cost device, that is working without any electronic or mechanic noise. It has to allow the correction of high order modes to improve the matching of high power laser beams in the interferometer.An experimental setup has been made to characterize the first prototype on air. An efficient process and a control loop have allowed to determine the possibilities and limits of the device. We have demonstrated its ability to correct high order modes of an infrared laser beam. Afterwards, we have validated the improvement of mode matching into a fixed cavity.

O detector de ondas gravitacionais Mário Schenberg consiste de uma massa ressonante esférica de Cu(94%)Al(6%) com 65cm de diâmetro, pesando aproximadamente 1,15T, com um Q mecânico da ordem de 106 e todos os sistemas que possibilitam o seu funcionamento como detector de ondas gravitacionais. O projeto do detector prevê para este uma sensibilidade da ordem de 10-20 (em deformação). Para isso dependerá da eficiência dos sistemas vibracionais que utiliza. Neste trabalho os casadores mecânicos de impedância, foram simulados com um programa de elementos finitos e otimizados quanto à sua banda e acoplamento vibracional. Foi feita a análise do sistema de isolamento vibracional da nova suspensão, por meio da resposta em frequência do ruído sísmico na superfície da esfera, nos mesmos locais onde estão conectados os transdutores. Foi proposto um projeto novo para atenuar os ruídos provenientes do cabeamento que conduz os sinais de micro-ondas. Foi avaliado o efeito do ruído sísmico introduzido na suspensão e na esfera, também nos locais dos transdutores, utilizando este novo projeto. É apresentado um projeto para a conexão térmica do refrigerador por diluição, que a análise por simulação numérica demonstrou ser eficaz. A modelagem para análise vibracional é a melhor já feita para detectores esféricos, isto se comparada às que foram encontrados na literatura. Os resultados alcançados demonstraram que as atenuação em todos os sistemas analisados são adequadas às metas do projeto do detector Mário Schenberg, ou seja, os ruídos remanescentes estão abaixo do ruído térmico esperado na temperatura de 50mK. / The Gravitational Wave detector Mario Schenberg consist of a spherical resonant-mass made of CuAl(6%) with 65 cm diameter e weighting 1.15 Ton, with a Mechanical quality factor of about 106 and all the systems that allows it to word as a gravitational wave detector. The detector design was made for it to reach a sensitivity of 10-20 (strain sensitivity). To reach this goal it depends on the efficiency of the it vibrational systems. In this work the transducers mechanical impedance matchers were simulated with a finite element program and optimized in its band and vibrational coupling. A analysis of the vibrational isolation of the new suspension was made by the frequency response of the seismic noise on the sphere surface, on the same places where they will be connected to the transducers. A new design for attenuation of the noise due to microwave cabling was proposed. The seismic noise introduced on the suspension and on the sphere was simulated using this new design. A design for the dilution refrigerator thermal connection is presented, and its performance is measured in a analysis in a finite element moddeling, and showed itself efficienty. This vibration model for the detector is the best one ever made for spherical detectors, if compared to the literature. Results obtained showed that the atennuation in all the analysed systems are compatible to the Mário Schenberg detector design goals, it means that, the remaining noises are below the expected thermal noise at the temperature of 50 mK.

La première partie de cette thèse traite des théories de gravité massive. L'étude de ces théories a connu un regain d'intérêt depuis la découverte de l'accélération de l'expansion de l'univers, car elles pourraient expliquer cette dernière sans avoir à recourir à une constante cosmologique. La découverte, en 2010 d'une théorie cohérente de gravité massive, dite dRGT, a ouvert un vaste et prometteur champ d'investigation. Dans cette thèse nous déterminons, dans une formulation métrique et covariante, la linéarisation autour d'espace-temps arbitraires de ces théories, et de leur extension bimétrique. Ce travail nous permet ensuite de compter par une méthode lagrangienne le nombre de degrés de liberté qui se propagent. La seconde partie de cette thèse s'inscrit dans le cadre des ondes gravitationnelles en relativité générale et porte plus précisément sur la dynamique de systèmes binaires d'objets compacts. Ce travail est important dans la perspective de leur détection par les détecteurs interférométriques d'ondes gravitationnelles terrestres et spatial. Nous étudions le problème de la dynamique de systèmes binaires d¿objets compacts en relativité générale, à l¿aide de la méthode d'approximation dites des développements post-newtoniens (PN). Nous dérivons les équations du mouvement à l'ordre $4$PN en coordonnées harmoniques. Nous utilisons une méthode basée sur une action de Fokker adaptée au formalisme post-newtonien, en dérivant notamment les effets de sillage d'onde qui apparaissent à $4$PN. / The first part of this thesis deals with massive gravity theories. There has been a renewal of interest in these theories since the discovery of the acceleration of the expansion of the universe, because they could explain it without having to resort to a cosmological constant. The discovery in 2010 of a coherent theory of massive gravity, named dRGT, has opened a vast and promising field of investigation. In this thesis we determine, in a metric and covariant formulation, the linearization around arbitrary backgrounds of these theories and their bimetric extension. This result then allows us to count with a Lagrangian method the number of degrees of freedom that are propagating. The second part of this thesis concerns gravitational waves in general relativity and especially the dynamics of coalescing compact binary systems. This work is important in view of their detection by interferometric detectors, both terrestrial and spacial. We study the dynamics of compact binary systems in general relativity, using the approximation method based on post-Newtonian developments (PN). We derive the equations of motion to $4$ PN order in harmonic coordinates. We use a method based on a Fokker action adapted to the post-Newtonian formalism, in particular deriving the tail effects appearing at $4$PN.

General relativity (GR) has stood as the most accurate description of gravity for the last 100 years, weathering a barrage of rigorous tests. However, attempts to derive GR from a more fundamental theory or to capture further physical principles at high energies has led to a vast number of alternative gravity theories. The individual examination of each gravity theory is infeasible and as such a systematic method of examining modified gravity theories is a necessity. Studying generic classes of gravity theories allows for general statements about observables to be made independent of explicit models. Take, for example, those models described by the Horndeski action, the most general class of scalar-tensor theory with at most second-order derivatives in the equations of motion, satisfying theoretical constraints. But these constraints alone are not enough for a given modified gravity model to be physically viable and hence worth studying. In particular, observations place incredibly tight constraints on the size of any deviation in the solar system. Hence, any modified gravity would have to mimic GR in such a situation. To accommodate this requirement, many models invoke screening mechanisms which suppress deviations from GR in regions of high density. But these mechanisms really upon non-linear effects and so studying them in complex models is mathematically complex. To constrain the space of actions of Horndeski type to those which pass solar-system tests, a set of conditions on the four free functions of the Horndeski action are derived which indicate whether a specific model embedded in the action possesses a GR limit. For this purpose, a new and surprisingly simple scaling method is developed, identifying dominant terms in the equations of motion by considering formal limits of the couplings that enter through the new terms in the modified gravity action. Solutions to the dominant terms identify regimes where nonlinear terms dominate and Einstein's field equations are recovered to leading order. Together with an efficient approximation of the scalar field profile, one can determine whether the recovery of Einstein's field equations can be attributed to a genuine screening effect. The parameterised post-Newtonian (PPN) formalism has enabled stringent tests of static weak-field gravity in a theory-independent manner. This is through parameterising common perturbations of the metric found when performing a post-Newtonian expansion. The framework is adapted by introducing an effective gravitational coupling and defining the PPN parameters as functions of position. Screening mechanisms of modified gravity theories can then be incorporated into the PPN framework through further developing the scaling method into a perturbative series. The PPN functions are found through a combination of the scaling method with a post-Newtonian expansion within a screened region. For illustration, we show that both a chameleon and cubic galileon model have a limit where they recover GR. Moreover, we find the effective gravitational constant and all PPN functions for these two theories in the screened limit. To examine how the adapted formalism compares to solar-system tests, we also analyse the Shapiro time delay effect for these two models and find no deviations from GR insofar as the signal path and the perturbing mass reside in a screened region of space. As such, tests based upon the path light rays such as those done by the Cassini mission do not constrain these theories. Finally, gravitational waves have opened up a new regime where gravity can be tested. To this end, we examine how the generation of gravitational waves are affected by theories of gravity with screening to second post-Newtonian (PN) order beyond the quadrupole. This is done for a model of gravity where the black hole binary lies in a screened region, while the space between the binary's neighbourhood and the detector is described by Brans-Dicke theory. We find deviations at both 1.5 and 2 PN order. Deviations of this size can be measured by the Advanced LIGO gravitational wave detector highlighting that our calculation may allow for constraints to be placed on these theories. We model idealised data from the black hole merger signal GW150914 and perform a best fit analysis. The most likely value for the un-screened Brans-Dicke parameter is found to be ω = -1:42, implying on large scales gravity is very modified, incompatible with cosmological results.

A existência de ondas gravitacionais foi confirmada indiretamente pela observação astronômica de pulsares binários. Detectores de ondas gravitacionais tem sido desenvolvidos desde o trabalho pioneiro de Weber nos anos 60. Esforços estão sendo realizados no sentido de aumentar a sensibilidade dos detectores e realizar uma detecção direta, que ainda não foi confirmada. O Grupo GRAVITON está aperfeiçoando e melhorando a sensibilidade de um detector de ondas gravitacionais que se encontra no Laboratório de Estado Sólido e Baixas Temperaturas do Instituto de Física da Universidade de São Paulo (LESBT/IFUSP), na cidade de São Paulo com apoio da FAPESP (processo 2006/56041-3). Esse detector, denominado MARIO SCHENBERG, é composto por uma massa ressonante esférica de CuAl(6%) com 65 cm de diâmetro, com aproximadamente 1150 kg, que deverá atingir a sensibilidade h ~ 10-22 em uma banda passante de 50 Hz, em torno de 3200 Hz, quando estiver operando a temperaturas da ordem de 0,05 K. Atualmente o detector já tem toda a sua infraestrutura criogênica montada e testada para resfriamentos a 4 K e toda a suspensão da esfera bem como todo o sistema de filtragem mecânica construídos e montados. Já foram realizadas as primeiras corridas comissionadas em 2006, 2007 e 2008, quando foram realizados vários diagnósticos sobre o sistema e desde então vem sendo desenvolvidos os transdutores para colocar o detector novamente em operação com melhor sensibilidade. Paralelamente, foram realizadas melhorias no próprio detector em razão dos diagnósticos realizados. O trabalho aqui apresentado está associado ao projeto acima. O autor desenvolveu atividades associadas à construção e desenvolvimentos do detector, que podem ser divididas em três partes principais: na parte mecânica, foi desenvolvido, instalado e testado um novo sistema de isolamento vibracional da suspensão da esfera; na parte criogênica foram feitas novas conexões térmicas, cálculos de gastos de hélio líquido e feitos desenvolvimentos para o funcionamento do refrigerador por diluição; e na parte eletrônica foi feita a instalação da eletrônica responsável pela transdução do sinal, além do desenvolvimento de um novo par de antenas de microfita. / The existence of gravitational waves has been confirmed indirectly by astronomical observation of binary pulsars. Gravitational wave detectors have been developed since the pioneering work of Weber in the 60s. Efforts are being made to increase the sensitivity of the detectors and perform a direct detection, wich has not been confirmed yet. The GRAVITON Group is enhancing and improving the sensitivity of a gravitational wave detector which is at the Laboratório de Estado Sólido e Baixas Temperaturas of the Instituto de Física of the Universidade de São Paulo (LESBT / IFUSP), in São Paulo city and is supported by FAPESP (processo 2006/56041-3). This detector, called MARIO SCHENBERG, consists of a spherical resonant mass of CuAl (6%) with 65 cm in diameter, and approximately 1150 kg, which should reach the sensitivity of h ~ 10-22 in a bandwidth of 50 Hz around 3200 Hz, when operating at temperatures of 0.05 K. Currently the detector already has all its infrastructure assembled and tested for cryogenic cooling down to 4 K and the whole suspension of the sphere as well as all mechanical isolation system constructed and assembled. Commissioning runs have already been done in 2006, 2007 and 2008, when several diagnoses on the system were performed and since then there have been many developments on the transducers to put back the detector into operation with improved sensitivity. At the same time, improvements have been made within the detector itself due to the diagnoses. The work presented here is associated with the above project. The author has developed activities and developments associated with the detector construction, which can be divided into three main parts: the mechanical part, in which a new system of vibration isolation was designed for the sphere suspension, installed and tested; the cryogenic part, in which new connections and thermal calculations of liquid helium boil-off rate were made as well as other developments for the operation of a dilution refrigerator; and the electronic part, in which the installation of the electronic signal responsable for the transduction was made, besides the development of a new pair of micro-strip antenna.

La détection ainsi que l’analyse des ondes gravitationnelles émises par les systèmes binaires d’objets compacts reposent sur notre capacité à faire des prédictions précises au sein de la théorie de la relativité générale. Dans cette thèse, nous utilisons la théorie post-newtonienne (PN), et en particulier le formalisme connu sous le nom de Blanchet-Damour-Iyer, afin d’étudier de tels systèmes. La finalité des différents calculs réalisés au sein de cette thèse est d’obtenir la phase du signal gravitationnel à l’ordre 4,5PN, et les résultats que nous présentons nous rapprochent fortement de cet objectif. Tout d’abord, nous calculons les sillages d’ondes à l’ordre 3 dans le champ radiatif, ce qui nous permet d’obtenir le coefficient 4,5PN du flux d’énergie émis par des systèmes binaires compacts sans spin dans le cas d’orbites circulaires. Puis, nous calculons la dernière ambiguïté apparaissant dans les équations du mouvement de deux corps compacts sans spin à l’ordre 4PN, ce qui nous permet d’obtenir la première dérivation à partir de principes fondamentaux de ce résultat. Nous étudions alors en détail les différentes quantités conservées générées par cette dynamique. Enfin,nous présentons un premier résultat préliminaire du quadrupôle de masse source à l’ordre 4PN, ce qui constitue l’une des étapes cruciales dans l’obtention de la phase à l’ordre 4.5PN. / The detection and the analysis of gravitational waves emitted by compact binary systems rely on our ability to make accurate predictions within general relativity. In this thesis, we use the post-Newtonian (PN) formalism, and in particular the Blanchet-Damour-Iyer framework, to study the dynamics and the emission of gravitational waves of such systems. The different computations that we performed are motivated by our aim to obtain the phase of the gravitational wave signal at the 4.5PN order. In that regard, crucial steps have been achieved within this thesis. First of all, we compute the third-order tail effects in the radiation field, yielding the 4.5PN coefficient of the energy flux for binaries of non-spinning objects in circular orbits. Besides, we determine the remaining ambiguity of the 4PN Lagrangian of two spinless compact bodies. This result completes the first derivation from first principles of the 4PN equations of motion. Then we comprehensively study the conserved quantities of the 4PN dynamics. Finally, we provide a preliminary result of the 4PN source mass quadrupole, which constitutes one of the crucial steps towards the computation of the 4.5PN phase.

<p>Gravitational waves and electromagnetic waves are important as carriers of energy and information. This thesis is devoted to the study of the propagation and interaction of these waves in plasmas, with emphasis on nonlinear effects and applications within astrophysics.</p><p>The physical systems are described by the Einstein-Maxwell-fluid equations or Einstein-Maxwell-Vlasov equations, when a kinetic treatment is required. The small amplitude and high-frequency approximation is employed for the gravitational waves, such that perturbative techniques can be applied and space-time can be considered locally flat, with a gravitational radiation field superimposed on it. The gravitational waves give rise to coupling terms that have the structure of effective currents in the Maxwell equations and an effective gravitational force in the equation of motion for the plasma. The Einstein field equations describe the evolution of the gravitational waves, with the perturbed energy-momentum density of the plasma and the electromagnetic field as a source.</p><p>The processes that are investigated are gravitational waves exciting electromagnetic waves in plasmas, altering the optical properties of plasmas and accelerating charged particles. The thesis also deals with the propagation propertities of gravitational and electromagnetic waves, e.g. effects due to resonant wave-particle interactions, plasma inhomogeneties and nonlinear self-interactions. It is also shown that plasmas that are not in thermodynamical equilibrium may release their free energy by emitting gravitational waves.</p>