Dissertationen zum Thema „Dark Matter Models“

Revealing the nature of the dark matter is among the most puzzling issues of today particle physics, astrophysics and cosmology. Given the striking evidences for dark matter at all astrophysical scales, starting from galactic and going to cosmological scales, a widespread and well motivated assumption on the nature of the dark matter is that it is made by a new particle that extends the Standard Models of Particle Physics. Indirect detection of dark matter, which annihilates in over-dense regions like the galactic centre, is an important probe of a possible dark matter interaction with the Standard Model particles. It could provide insights both to the underlying production mechanism of dark matter in the early Universe, on the annihilation properties at present time in galactic halos and on the underlying particle physics model. In this master thesis project we will focus on simplified leptophilic models for dark matter. These models feature an massive boson, called for instance Z', and a Dirac dark matter candidate, that complement the Standard Model of particle physics. We will study the annihilation of dark matter into leptons, focusing in particular on neutrino lines and box-shaped energy spectra. These tow signals are smoking gun signature to discover the dark matter properties. We will perform a numerical analysis using the dark matter software MadDM to predict the expected flux from the galactic centre, by performing scans in the model parameter space. We will implement the constrains from the Fermi-LAT telescope and the XENON1T experiment. Finally we will use the predictions of those models to assess the reach of the future KM3NeT neutrino telescope.

Una enorme quantità di evidenze sperimentali sulla esistenza di una forma di materia non luminosa nell'Universo, si sono accumulate nel corso di circa un secolo. Chiarire la sua natura è diventata una delle sfide più eccitanti ed urgenti negli sforzi per capire il nostro Universo. In questo lavoro presento uno studio su un approccio per scoprire la Materia Oscura interpretata come particella elementare e sulla possibilità di produrla e rilevarla negli acceleratori. Nella parte introduttiva presento una breve storia delle evidenze astrofisiche e astronomiche che hanno portato alla ipotesi della esistenza di Materia Oscura. Assumendo che la Materia Oscura sia costituita da una particella elementare ulteriore a quelle predette dal Modello Standard, delineo poi i tre principali metodi di rilevazione utilizzati attualmente per identificarla. Nella seconda parte discuto come si possono costruire teorie nelle quali sia possibile interpretare le ricerche attuali ed i risultati corrispondenti. Eseguo un confronto tra approcci diversi, partendo da modelli completi fino a quelli che utilizzano teorie di campo effettive. In particolare, discuto i loro lati positivi e negativi, motivando l'utilizzo di uno schema intermedio, il cosiddetto approccio con modelli semplificati, caratterizzati da un numero limitato di nuovi stati e parametri e che supera le limitazioni intrinseche delle teorie effettive nel contesto delle ricerche negli acceleratori. Nell'ultima parte fornisco una esaustiva classificazione dei modelli semplificati nel canale t, che non sono ancora stati analizzati sistematicamente nella letteratura. Per ciascuno di essi presento un possibile completamento UV e i segnali più promettenti ad LHC. Per questa ragione tutti i modelli considerati sono stati implementati in strumenti Monte Carlo, validati nel confronto con risultati analitici, studiati in dettaglio e resi pronti per un rilascio pubblico per la comunità fenomenologica e sperimentale di LHC.

We investigate models of composite dark matter in which the dark matter candidate arises naturally as an accidentally stable bound state of a confining dynamics and with observable signatures in a wide variety of experiments. In the first part of the thesis we introduce and explore a new class of models with dark fermions in the adjoint repre- sentation of the confining gauge group. The low energy dynamics and the cosmological history are peculiar and provide a dark matter candidate with properties much different from that of a canonical WIMP. The dark matter is heavy but has a large interaction range and can be tested primarily with indirect searches. In the second part of the thesis we classify and study models of composite dark matter with a strongly interacting chiral dark sector, in which all the mass scales are generated dynamically. In this case the candidate is a SM singlet dark pion with a thermal abundance whose low energy phenomenology can be thoroughly studied through chiral lagrangian techniques. We present an analysis of the low energy phenomenology, compute the radiatively generated masses of the light states and study the cosmological history of the model. The presence of partner states interacting with the SM offers the opportunity to test the model at colliders. In the last part of the thesis we present the phenomenological signatures of the models previously introduced and determine the current bounds. In doing so we also present a strategy to derive a limit on the lifetime of dark matter particles in generic models of particle dark matter from the observation of the 21 cm cosmological signal.

At present, the best model for the Universe as a whole is given by the so called ``Hot Big Bang'', which describes an expanding universe in which the density and temperature of matter and radiation are followed in time. The value of the parameters characterizing the observed universe is summarized by the concordance $\Lambda$CDM model, where CDM stands for Cold Dark Matter (the main matter component), and $\Lambda$ is the cosmological constant (some kind of unknown energy, with an anti-gravitational effect). According to this model, the universe is spatially flat (i.e. the density parameter $\Omega$ equals one), and 75\% of its energy balance is assigned to dark energy, about 20\% to dark matter and about 5\% to ordinary (baryonic) matter; the expansion speed assumes a value $H_{0}=70.5$ Km/s/Mpc (the Hubble parameter). The present dissertation focuses on the distribution of dark matter into virialized structures, called dark matter haloes. According to structure formation theory, cosmic structures originates from the amplification of quantum fluctuations during an early stage of accelerated expansion (cosmic inflation); these perturbations grow by self-gravity until they collapse and originate virialized structures. In the linear regime (when fluctuations are small), this process is well understood by the Jeans' theory. The non linear regime is much harder to describe; erlier attempts assumed a simple spherical simmetry, where the collapse is driven only by the internal density (e.g. Peebles, 1980); more recently (White \& Silk 1979; Bond \& Myers 1996) this hypothesis has been relaxed, and a more complex model was proposed in which proto-structures are described by triaxial ellipsoids, governed by their internal density and shape. Using the results coming from the dynamical analysis of the spherical collapse, and exploiting the statistical ``excursion sets formalism'', it is possible to obtain analytical information about the mass distribution of dark matter haloes. In this approach, for each particle in the universe, the trajectory describing the density evolution of a sphere of matter built around that particle is modeled as a random walk as a function of the mass $M$ within that sphere. When a trajectory crosses some pre-defined threshold, one assumes that a virialized structure of mass $M$ has formed. By considering all the particles in the universe one obtains analytical forms for the global mass function, and for the progenitor and descendant mass functions. From these it is possible to calculate other quantities, like the (instantaneous and integrated) rates of creation and destruction of dark matter haloes. In the 1990's the ellipsoidal collapse was first tried in order to find a better match with numerical simulations. However, partly due to the analytical complexity of the model, until now one can still not find in the literature analytical forms for e.g. the descendant and merger rate distributions (see Table \ref{tab:scec}). The main goal of this work is to provide such expressions for a number of statistics related to the mass distributions of dark matter haloes, striving to obtain simple and accurate formulas. In order to do so, we start from the statistical considerations by Sheth, Mo e Tormen (2001), who introduced the dynamical effects of the ellipsoidal collapse into the excursion sets formalism just by modifying the shape of the density threshold. Sheth and Tormen (2002) further suggested an new expression for the ellipsoidal global mass function, using a Taylor expansion series for the barrier: this expression allows one to also derive analytical formulas for the conditional mass functions. We obtain a set of models changing the order of this Taylor expansion, and considering the normalization of the distribution as a free parameter; we then compare these equations with the results of the cosmological simulation Gif2 (Gao et al. 2004) and, in some cases, with the Millennium Simulation (Springel et al. 2005). For the global and conditional mass functions the match between models and simulations is estimated using a $\chi ^2$-method. For the merger rates we compare the results qualitatively, whereas for the creation rates we only derived analytical results. We especially focus on the cases providing the simplest analytical expressions: the zero-order and the infinite-orders Taylor series. In the last part of the dissertation we propose a new statistical method that can overcome two inconvenients of $\chi ^2$-methods: (i) data binning and (ii) neglect of field particles (dust) in simulations. Concerning point (i), different bin-sizes can lead to small differences in the $\chi ^2$-results. As for point (ii), particles that are not bound to haloes are usually considered only for computing the normalization. By using a maximum likelihood analysis we can treat unbinned data, as well as take into account dust in the determination of the best parameters of the mass function. Our tests are performed by comparing a two-parameter mass function with results of Monte Carlo simulations. Our work naturally settles within the systematic search of analytical expressions associated to the ellipsoidal collapse of dark matter haloes. Since haloes are thought to be the sites where baryons can condense and form stars, galaxies and other luminous objects, the expression we derive can be used for a number of applications, ranging from unveiling the nature of dark matter through self-annihilation, to the understanding of the mechanisms leading to galaxy formation. Furthermore, the description of galaxy evolution requires knowledge on the hosting haloes: semi-analytical models of galaxy formation depend on the global mass function of the dark matter haloes, and the corrisponding merger-trees are based on the progenitor mass functions. The rates of creation and destruction are useful to compute the abundances of objects like Active Galactic Nuclei (AGNs) and Super Massive Black Holes (SMBHs). Many other examples can be found in the literature for the use of dark matter distributions in studies of galaxy formation. The structure of the dissertation is as follows: {\bf Chapters 1} justifies the need of dark matter. In {\bf Chapters 2} we present the concordance cosmological model, its geometry and thermal history. We also introduce the linear and non-linear models for the formation of dark matter haloes. {\bf Chapter 3} describes the excursion sets approach in the framework of the spherical collapse. The extension of this method to the ellipsoidal collapse is given in {\bf Chapter 4}, where the firsts analytical results are derived. In {\bf Chapter 5} we compare our analytical predictions to a number of results from numerical simulations. {\bf Chapter 6} is devoted to the new maximum likelihood tests with unbinned data and dust particles. We finally draw our {\bf Conclusions}, followed by one {\bf Appendix} where the numerical simulations are described.
La miglior descrizione dell'Universo, di cui si dispone al momento, è il modello del ``Big Bang Caldo'', che contempla un universo in espansione nel quale viene seguita l'evoluzione temporale della densità e della temperatura della materia e della radiazione. I parametri che caratterizzano l'Universo osservato sono riassunti in un modello chiamato $\Lambda$CDM di concordanza: CDM sta per Cold Dark Matter (la componente dominante della materia), e $\Lambda$ è la costante cosmologica (una sorta di energia oscura, con effetto anti-gravitazionale). Secondo questo modello, l'universo è spazialmente piatto (cioè il parametro di densità $\Omega$ è uguale a uno), e il $75\%$ del suo bilancio energetico è assegnato all'energia oscura, circa il $20\%$ alla materia oscura e circa il $5\%$ alla materia ordinaria (barioni); la velocità dell'espansione assume il valore $70.5$ Km/s/Mpc (parametro di Hubble). Questa tesi si sofferma sulla distribuzione della materia oscura in strutture virializzate, chiamate aloni di materia oscura. Secondo la teoria di formazione delle strutture, le strutture cosmiche hanno origine dall'amplificazione di fluttuazione quantistiche durante un periodo iniziale di espansione accelerata (inflazione cosmica); queste perturbazioni crescono per effetto dell'autogravità fino al collasso, creando delle strutture virializzate. Durante il regime lineare (quando le fluttuazioni sono piccole), questo processo è ben descritto dalla teoria di Jeans. Il regime non lineare è molto più difficile da descrivere; i primi tentativi assumono una simmetria sferica, per la quale il collasso è descritto solo dalla densità interna (es. Peebles, 1980); più recentemente (White \& Silk 1979; Bond \& Myers 1996) questa ipotesi è stata rilassata, ed è stato proposto un modello più complesso nel quale le protostrutture sono descritte da ellissoidi triassiali, regolati dalla loro densità interna e dalla loro forma. Utilizzando i risultati ottenuti dall'analisi dinamica del collasso sferico e sfruttando il formalismo statistico degli ``excursion set'', è possibile ottenere informazioni analitiche in merito alla distribuzione di massa degli aloni di materia oscura. In questo approccio, per ogni particella nell'universo, la traiettoria che descrive l'evoluzione della densità della sfera di materia costruita attorno a quella particella viene modellata come un cammino browniano come funzione della massa $M$ all'interno della sfera. Quando una traiettoria interseca una pre-definita soglia, si assume che venga a formarsi una struttura virializzata di massa $M$. Considerando tutte le particelle dell'universo, si ottengono forme analitiche per la funzione di massa globale, e per le funzioni di massa dei progenitori e dei figli. Da queste, è possibile calcolare altre quantità, come i tassi di creazione e distruzione (istantanei e integrati). Negli anni '90, il collasso ellissoidale è stato utilizzato per trovare un miglior accordo con le simulazioni numeriche. Tuttavia, in parte a causa della complessità analitica del modello, fino ad ora non è stato ancora possibile trovare in letteratura forme analitiche per esempio per la funzione dei figli o per i tassi di distruzione (vedi Tabella \ref{tab:scec}). l'obiettivo principale di questo lavoro è di fornire tali espressioni per una serie di funzioni legate alle distribuzione di massa degli aloni di materia oscura, aspirando ad ottenere delle formule semplici ed accurate. Per farlo, siamo partiti dalle considerazioni statistiche di Sheth, Mo e Tormen (2001) che introducono gli effetti dinamici del collasso ellissoidale nel formalismo excursion sets, modificando la forma della soglia di densità. Sheth e Tormen (2002), inoltre, propongono una nuova espressione per la funzione di massa globale ellissoidale, usando uno sviluppo in serie di Taylor per la barriera: questa espressione permette di derivare forme analitiche anche per le funzioni di massa condizionali. Abbiamo ottenuto un set di modelli cambiando l'ordine di questo sviluppo di Taylo, e considerando la normalizzazione delle distribuzioni come un parametro libero; abbiamo poi confrontato queste equazioni con i risultati della simulazione cosmologica Gif2 (Gao et al. 2004) e, in alcuni casi, con la Millennium Simulation (Springel et al. 2005). Per le funzioni di massa globale e condizionali, l'accordo tra modelli e simulazioni è stimato usando un metodo $\chi ^2$. Per i merger rates abbiamo confronti qualitativi, mentre per i tassi di creazione abbiamo derivato le sole equazioni analitiche. Ci siamo soffermati specialmente sui casi che forniscono le espressioni analiticamente più semplici: le serie di Taylor con zero ordini e con infiniti ordini. Nell'ultima parte della tesi, proponiamo un nuovo metodo statistico che può scartare gli inconvenienti dei metodi $\chi ^2$: (i) la divisione in intervalli dei dati e (ii) il trascurare le particelle di campo (polvere) delle simulazioni. Per quanto riguarda il punto (i), differenti ampiezze degli internalli di massa possono portare a piccole differenze nei risultati del $\chi^2$. Il punto (ii) si riferisce al fatto che le particelle che non sono legate in aloni sono di solito considerate solo per il calcolo della normalizzazione. Usando un'analisi di massima verosimiglianza, possiamo trattare dati non raggruppati in intervalli e considerare la polvere nella determinazione dei parametri migliori per la funzione di massa. I nostri tests sono condotti confrontando una funzione di massa a due parametri con i risultati di simulazioni Monte Carlo. Il nostro lavoro si inserisce naturalmente nella ricerca sistematica delle espressioni analitiche associate al collasso ellissoidale degli aloni di materia oscura. Poichè si pensa che gli aloni siano i siti ove i barioni possono concentrarsi e formare stelle, galassie ed altri oggetti luminosi, le espressioni che otteniamo possono essere usate in varie applicazioni, dallo svelare la natura della materia oscura attraverso l'auto annichilazione, fino alla comprensione dei meccanismi che portano alla formazione galattica. Inoltre, la descrizione dell'evoluzione galattica richiede la conoscenza dell'alone correlato: i modelli semi-analitici di formazione galattica dipendono dalla funzione di massa globale degli aloni di materia oscura, e i corrispondenti merger-trees sono basati sulle funzioni di massa dei progenitori. I tassi di creazione e distruzione sono utili per calcolare le abbondanze di oggetti come Nuclei Galattici Attivi (AGN) e Buchi Neri Super Massicci (SMBH). Altri esempi dell'utilizzo delle distribuzioni della materia oscura in studi di formazione galattica si possono trovare copiosi in letteratura.\\ L'elaborato si articola in questo modo: il {\bf Capitoli 1} giustifica la necessità della materia oscura. Nel {\bf Capitolo 2} presentiamo il modello cosmologico di concordanza, la sua geometria e la storia termica. Inoltre, introduciamo i modelli, lineare e non lineare, di formazione degli aloni di materia oscura. Il {\bf Capitolo 3} descrive l'approccio degli excursion sets nel contesto del collasso sferico. L'estensione di questo metodo al collasso ellissoidale è proposto nel {\bf Capitolo 4}, ove vengono esposti i primi risultati analitici. Nel {\bf Capitolo 5} confrontiamo le nostre predizioni analitiche con i risultati di due simulazioni numeriche. Il {\bf Capitolo 6} è dedicato all'esposizione dei test di un nuovo metodo di massima verosimiglianza con l'utilizzo di dati non raggruppati in intervalli e con le particelle di polvere. Infine tracciamo le nostre {\bf Conclusioni}, seguite da un'{\bf Appendice} ove sono descritte le simulazioni numeriche.

La teoría científica de más éxito hoy en día, sobre el origen y la evolución del universo, es conocida como el modelo estándar del Big Bang, el cual es una de las construcciones intelectuales más ambiciosas de la humanidad. Se basa en dos ramas bien consolidadas de la física teórica, a saber, la teoría de la Relatividad General y el Modelo Estándar de la física de partículas, y es capaz de hacer predicciones sólidas, como la expansión del universo, la existencia del fondo de radiación de microondas y las abundancias relativas de los elementos ligeros. Algunas de las predicciones teóricas ya han sido confirmadas por observaciones muy precisas.
Según la cosmología estándar del Big Bang, el universo primitivo consistía en un plasma muy caliente y denso que se expandió y se enfrió continuamente hasta el presente, dando paso a una serie de transiciones de fase cosmológicas, donde las teorías que describen el universo en cada fase son distintas. Dado que las energías del universo primitivo fueron mucho más altas que las alcanzadas en experimentos terrestres, el estudio del universo primitivo podría ofrecernos importantes informaciones sobre nuevas interacciones y nuevas partículas, abriendo nuevas direcciones para la extensión del Modelo Estándar de la física de partículas.
Como ya he mencionado anteriormente, durante la expansión del universo ocurrieron varias transiciones de fase que dejaron su huella sobre el estado presente del universo. Las observaciones sugieren que durante una de estas transiciones de fase, el universo primitivo sufrió un periodo de expansión acelerada, conocido como inflación. Aunque no forma parte de la cosmología estándar, la inflación es capaz de solucionar de una manera simple y elegante casi todos los problemas relacionados con el modelo estándar del Big Bang, y debería tenerse en cuenta en cualquier extensión posible de la teoría. Las observaciones también revelan la existencia de dos formas de energía desconocidas, a saber, materia oscura y energía oscura. La materia oscura es una forma de materia no relativista y no bariónica, que solamente puede ser detectada indirectamente, mediante su interacción con la materia normal. La energía oscura es un tipo de sustancia con presión negativa, que empezó a dominar recientemente y que es la causa de la aceleración de la expansión del universo.
En esta tesis doctoral presento varios modelos originales propuestos para resolver algunos de los problemas de la cosmología estándar, como posibles extensiones del modelo del Big Bang. Algunos de estos modelos introducen nuevas simetrías y partículas con el fin de explicar la inflación y la energía oscura y/o la materia oscura en una descripción unificada. Uno de los modelos es propuesto para explicar la energía oscura del universo, a través de un nuevo campo escalar que oscila en un potencial.
The most successful scientific theory today about the origin and evolution of the universe is known as the standard Big Bang model, which is one of the most ambitious intellectual constructions of the humanity. It is based on two consolidated branches of theoretical physics, namely, the theory of General Relativity and the Standard Model of particle physics, and is able to make robust predictions, such as the expansion of the universe, the existence of the cosmic microwave background radiation and the relative primordial abundance of light elements. Some of the theoretical predictions have already been confirmed by very precise observations.
According to the standard Big Bang cosmology, the early universe consisted of a very hot and dense plasma that continuously expanded and cooled up to the present, giving place to a series of cosmological phase transitions, where the theories describing the universe in each phase are different. Given that the energies of the early universe were much higher than those reached in terrestrial experiments, the study of the early universe might give us important information about new interactions and new particles, opening new directions for extending the Standard Model of particle physics.
As already mentioned above, during the expansion of the universe, different phase transitions occurred, which left their imprint on the present state of the universe. Observations suggest that during a very early phase transition the universe suffered a stage of accelerated expansion, known as inflation. Although inflation is not included in the standard cosmology, it is able to solve in a simple and elegant manner almost all of the shortcomings related to the standard Big Bang model, and should be taken into account in any possible extension of the theory. Observations also reveal evidence of the existence of two unknown forms of energy, i.e., dark matter and dark energy. Dark matter is a form of non-relativistic and non-baryonic matter, which can only be detected indirectly, by its gravitational interactions with normal matter. Dark energy is a kind of substance with negative pressure, which started to dominate recently and causes the accelerated expansion of the universe.
In this PhD Thesis, I present a few original models proposed to solve some of the shortcomings of the standard cosmology, as possible extensions of the Big Bang model. Some of these models introduce new symmetries and particles in order to explain inflation and dark energy and/or dark matter in a unified description. One of the models is proposed for explaining the dark energy of the universe, by means of a new scalar field oscillating in a potential.
The most successful scientific theory today about the origin and evolution of the universe is known as the standard Big Bang model, which is one of the most ambitious intellectual constructions of the humanity. It is based on two consolidated branches of theoretical physics, namely, the theory of General Relativity and the Standard Model of particle physics, and is able to make robust predictions, such as the expansion of the universe, the existence of the cosmic microwave background radiation and the relative primordial abundance of light elements. Some of the theoretical predictions have already been confirmed by very precise observations.
According to the standard Big Bang cosmology, the early universe consisted of a very hot and dense plasma that continuously expanded and cooled up to the present, giving place to a series of cosmological phase transitions, where the theories describing the universe in each phase are different. Given that the energies of the early universe were much higher than those reached in terrestrial experiments, the study of the early universe might give us important information about new interactions and new particles, opening new directions for extending the Standard Model of particle physics.
As already mentioned above, during the expansion of the universe, different phase transitions occurred, which left their imprint on the present state of the universe. Observations suggest that during a very early phase transition the universe suffered a stage of accelerated expansion, known as inflation. Although inflation is not included in the standard cosmology, it is able to solve in a simple and elegant manner almost all of the shortcomings related to the standard Big Bang model, and should be taken into account in any possible extension of the theory. Observations also reveal evidence of the existence of two unknown forms of energy, i.e., dark matter and dark energy. Dark matter is a form of non-relativistic and non-baryonic matter, which can only be detected indirectly, by its gravitational interactions with normal matter. Dark energy is a kind of substance with negative pressure, which started to dominate recently and causes the accelerated expansion of the universe.
In this PhD Thesis, I present a few original models proposed to solve some of the shortcomings of the standard cosmology, as possible extensions of the Big Bang model. Some of these models introduce new symmetries and particles in order to explain inflation and dark energy and/or dark matter in a unified description. One of the models is proposed for explaining the dark energy of the universe, by means of a new scalar field oscillating in a potential.

In this thesis we go beyond the standard cosmological LCDM model and study the effect of an interaction between dark matter and dark energy. Although the LCDM model provides good agreement with observations, it faces severe challenges from a theoretical point of view. In order to solve such problems, we first consider an alternative model where both dark matter and dark energy are described by fluids with a phenomenological interaction given by a combination of their energy densities. In addition to this model, we propose a more realistic one based on a Lagrangian density with a Yukawa-type interaction. To constrain the cosmological parameters we use recent cosmological data, the CMB measurements made by the Planck satellite, as well as BAO, SNIa, H0 and Lookback time measurements.
Nesta tese vamos além do modelo cosmológico padrão, o LCDM, e estudamos o efeito de uma interação entre a matéria e a energia escuras. Embora o modelo LCDM esteja de acordo com as observações, ele sofre sérios problemas teóricos. Com o objetivo de resolver tais problemas, nós primeiro consideramos um modelo alternativo, onde ambas, a matéria e a energia escuras, são descritas por fluidos com uma interação fenomenológica dada como uma combinação das densidades de energia. Além desse modelo, propomos um modelo mais realista baseado em uma densidade Lagrangiana com uma interação tipo Yukawa. Para vincular os parâmetros cosmológicos usamos dados cosmológicos recentes como as medidas da CMB feitas pelo satélite Planck, bem como medidas de BAO, SNIa, H0 e Lookback time.

In this thesis we studied dark matter models with strong self-interactions, typically known as self-interacting dark matter (SIDM). This kind of models constitute a promising solution to the tension between small scale structure observations and predictions assuming the standard case of collisionless cold dark matter (CDM) while keeping the success of the standard cosmological model, LambdaCDM, at large scales. The presence of strong self-interactions can increase the dark matter capture and annihilation in astrophysical objects like our sun, enhancing the potential of indirect detection signals. We used the high energy neutrinos produced by such annihilations to probe SIDM models. We established strong constraints on SIDM with velocity independent cross section by comparing the expected neutrino signal with the results of the IceCube-79 dark matter search. Also, we determined the sensitivity for the IceCube-DeepCore and PINGU detectors for SIDM with a velocity dependent self-interacting cross section (vdSIDM). Most of its relevant parameter space can be tested with the three years of data already collected by IceCube-DeepCore, complementing results from direct detection experiments and other indirect detection studies.
Nesta tese investigamos modelos de matéria escura com auto-interações fortes, conhecidos tipicamente como matéria escura auto-interagente (SIDM). Este tipo de modelos constituem uma solução promissora à tensão entre as observações de estrutura a pequena escala e as previsões assumindo o caso padrão de matéria escura fria não colisional (CDM), enquanto se mantêm o sucesso do modelo cosmológico padrão, LambdaCDM, a grandes escalas. A presença de auto-interações fortes podem aumentar a captura e a aniquilação da matéria escura em objetos astrofísicos como o nosso sol, aumentando o potencial de sinais de detecção indireta. Usamos o sinal de neutrinos de alta energia produzidos por essas aniquilações para explorar modelos de SIDM. Estabelecemos fortes vínculos em modelos de SIDM com seção de auto-interação independente da velocidade comparando o sinal de neutrinos esperado com os resultados de busca de matéria escura do IceCube-79. Também, determinamos a sensibilidade dos detectores IceCube-DeepCore e PINGU para modelos de SIDM com uma seção de auto-interação dependente da velocidade (vdSIDM). A maior parte do espaço de parâmetros de interesse pode ser testado com os três anos de dados já coletados pelo IceCube-DeepCore, complementando os resultados de experimentos de detecção direta e outras an análises de detecção indireta.

This thesis explores topics related to the formation and development of the large-scale structure in the Universe, with the focus being to compute properties of the evolved non-linear density field in an approximate way. The first three chapters form an introduction: Chapter 1 contains the theoretical basis of modern cosmology, Chapter 2 discusses the role of N-body simulations in the study of structure formation and Chapter 3 considers the phenomenological halo model. In Chapter 4 a novel method of computing the matter power spectrum is developed. This method uses the halo model directly to make accurate predictions for the matter spectrum. This is achieved by fitting parameters of the model to spectra from accurate simulations. The final predictions are good to 5% up to k = 10 hMpc-1 across a range of cosmological models at z = 0, however accuracy degrades at higher redshift and at quasi-linear scales. Chapter 5 is dedicated to a new method of rescaling a halo catalogue that has previously been generated from a simulation of a specific cosmological model to a different model; a gross rescaling of the simulation box size and redshift label takes place, then individual halo positions are modified in accord with the large scale displacement field and their internal structure is altered. The final power spectrum of haloes can be matched at the 5% level up to k = 1 hMpc-1, as can the spectrum of particles within haloes reconstituted directly from the rescaled catalogues. Chapter 6 applies the methods of the previous two chapters to modified gravity models. This is done in as general a way possible but tests are restricted to f(R) type models, which have a scale-dependent linear growth rate as well as having 'chameleon screening' - by which modifications to gravity are screened within some haloes. Taking these effects into account leads to predictions of the matter spectrum at the 5% level and rescaled halo distributions that are accurate to 5% in both real and redshift space. For the spectrum of halo particles it is demonstrated that accurate results may be obtained by taking the enhanced gravity in some haloes into account.

Scientific curiosity and thirst for knowledge have driven human progress and helped mankind develop an always deeper understanding of our world. New - and sometimes controversial - ideas have been proposed in order to explain its mysteries. Looking for alternative perspectives has proven essential, particularly when the current paradigms do not give complete satisfaction. Such is the case for three important questions in modern astrophysics and cosmology, which we intend to investigate: the Paradox of Youth, Dark Matter and Dark Energy. We will first explore a new possible explanation to the paradoxical observation of young, massive stars near the centre of our galaxy. Hosting a solar mass black hole might allow them to spare some of their burning material, giving them enough time to travel from further galactic distances. In the second part of our thesis, we will study Dark Matter accretion onto neutron stars. Considering different types of Dark Matter particles, we will determine the consequences of their capture by these very dense objects and look for observable signatures. Finally, our current views on Dark Energy will be examined through its role in void models. Among them, the Swiss-Cheese Universe and central void models will be analysed in order to evaluate the impact of inhomogeneities on the determination of cosmological parameters. All three parts are similarly structured: conceptual introduction, analytical and computational considerations, commented results and conclusive remarks. Bibliographies are given separatly after each part. Lists of figures, tables and abbreviations can be found at the end of the document.

>Magister Scientiae - MSc
The growth of structure in the Universe proceeds via the collapse of dark matter and baryons. This process is retarded by dark energy which drives an accelerated expansion of the late Universe. In this thesis we use cosmological perturbation theory to investigate structure formation for a particular class of dark energy models, i.e. interacting dark energy models. In these models there is a non-gravitational interaction between dark energy and dark matter, which alters the standard evolution (with non-interacting dark energy) of the Universe. We consider a simple form of the interaction where the energy exchange in the background is proportional to the dark energy density. We analyse the background dynamics to uncover the e ect of the interaction. Then we develop the perturbation equations that govern the evolution of density perturbations, peculiar velocities and the gravitational potential. We carefully account for the complex nature of the perturbed interaction, in particular for the momentum transfer in the dark sector. This leads to two di erent types of model, where the momentum exchange vanishes either in the dark matter rest-frame or the dark energy rest-frame. The evolution equations for the perturbations are solved numerically, to show how structure formation is altered by the interaction.

In this dissertation, we investigate various aspects of dark matter detection and model building. Motivated by the cosmic ray positron excess observed by PAMELA, we construct models of decaying dark matter to explain the excess. Specifically we present an explicit, TeV-scale model of decaying dark matter in which the approximate stability of the dark matter candidate is a consequence of a global symmetry that is broken only by instanton-induced operators generated by a non-Abelian dark gauge group. Alternatively, the decaying operator can arise as a Planck suppressed correction in a model with an Abelian discrete symmetry and vector-like states at an intermediate scale that are responsible for generating lepton Yukawa couplings. A flavor-nonconserving dark matter decay is also considered in the case of fermionic dark matter. Assuming a general Dirac structure for the four-fermion contact interactions of interest, the cosmic-ray electron and positron spectra were studied. We show that good fits to the current data can be obtained for both charged-lepton-flavor-conserving and flavor-violating decay channels. Motivated by a possible excess of gamma rays in the galactic center, we constructed a supersymmetric leptophilic higgs model to explain the excess. Finally, we consider an improvement on dark matter collider searches using the Razor analysis, which was originally utilized for supersymmetry searches by the CMS collaboration.

Un des problèmes les plus intrigants de la physique moderne est l'identification de la nature d'une composante de matière non-relativiste présente dans l'univers, contribuant à plus de 25% de sa densité d'énergie totale, appelée matière noire. Les particules "WIMPs" (Weakly Interacting Massive Particles) sont parmi les catégories de candidats à la matière noire les plus considérées. Cependant, en l'absence de résultats concluants d'expériences de détection directe, indirecte et auprès de collisionneurs de particules, la première partie de cette thèse est dévouée à l'étude du paradigme "WIMP" dans le contexte de modèles simplifiés. Des modèles considérant des extensions de jauge sont étudiés par la suite tels que des théories présentant des couplages de Chern-Simons ainsi qu'un modèle motivé par l'observation récente d'anomalies dans le domaine de la physique la saveur lié à l'observable RK(*). La deuxième partie de cette thèse est dévouée à l'étude de mécanismes alternatifs de production thermique de matière noire en particulier en considérant une réalisation spécifique du mécanisme "SIMP" (Strongly Interacting Massives Particles) dans le contexte d'une symétrie de jauge non-abélienne cachée. Dans une dernière partie, la possibilité de produire une composante de matière noire de manière non-thermique à travers le mécanisme "freeze-in" est étudiée. En particulier, le fort impact de l'époque post-inflationnaire de l'univers sur la production de densité de matière noire est illustré par l'étude d'un modèle de matière noiremédiée par un champ de spin 2 massif en plus du graviton standard
One of the most puzzling problems of modern physics is the identification of the nature a non-relativistic matter component present in the universe, contributing to more than 25% of the total energy budget, known as Dark Matter. Weakly Interacting Massive Particles (WIMPs) are among the best motivated dark matter candidates. However, in light of non conclusive detection signals and strong constraints from collider, direct and indirect detection experiments, this thesis presents constraints on several realizations of the WIMP paradigm in the context of simplified dark matter models. More elaborated models considering extended gauge structures are discussed further on, such as constructions involving generalized Chern-Simons couplings and a specific WIMP scenario motivated by some recently observed flavor anomalies related to the RK(*) observable. The second part of this thesis is devoted to the discussion of an alternative dark matter thermal production mechanism where an explicit realization of the Strongly Interacting Massive Particles (SIMPs) paradigm is discussed in the context of a non-Abelian hidden gauge structure. In a last part, the possibility of producing non-thermally a dark matter component via the "freeze-in" mechanism was investigated and the strong impact of the postinationary reaheating stage of the universe on such constructions illustrated by the specific case where dark matter density production is mediated by a heavy spin-2 field in addition to the standard graviton

Despite its indisputable successes, the Standard Model of particle physics (SM) is widely considered to be an effective low-energy approximation to an underlying theory that describes physics at higher energy scales. While there are many candidates for such a theory, nearly all of them predict the existence of additional particles beyond those of the Standard Model. In this work, we present three analyses aimed at discovering new particles at current and future particle colliders. The first two analyses are designed to probe extended scalar sectors, which often arise in theories beyond the Standard Model (BSM). The structure of these extended scalar sectors can be described by a physically well-motivated class of models, known collectively as Two- Higgs Doublet Models (2HDMs). The scalar mass spectrum of 2HDMs is comprised of two CP-even states h and H, a CP-odd state A, and a pair of charged states H± . Traditional searches for these states at particle colliders focus on finding them via their decays to SM particles. However, there are compelling scenarios in which these heavy scalars decay through exotic modes to non-SM final states. In certain regions of parameter space, these exotic modes can even dominate the conven- tional decay modes to SM final states, and thus provide a complementary avenue for discovering new Higgs bosons. The first analysis presented aims to discover charged Higgs bosons H± via top decay at the LHC. We find that the exotic decay modes outperform the conventional decay modes for regions of parameter space with low values of the 2HDM parameter tan β. The second analysis aims to systematically cover all the exotic decay scenarios that are consistent with theoretical and experimental con- straints, at both the 14 TeV LHC and a future 100 TeV hadron collider. We find that the preliminary results are promising - we are able to ex- clude a large swathe of 2HDM parameter space, up to scalar masses of 3.5 TeV, for a wide range of values of tan β, at a 100 TeV collider. In addition to these two analyses, we also present a third, aimed at discovering pair produced higgsinos that decay to binos at a 100 TeV collider. Higgsinos and binos are new fermion states that arise in the Minimal Supersymmetric Standard Model (MSSM). This heavily- studied model is the minimal phenomenologically viable incorporation of supersymmetry - a symmetry that connects fermions and bosons - into the Standard Model. In the scenario we consider, the bino is the lightest supersymmetric partner, which makes it a good candidate for dark matter. Using razor variables and boosted decision trees, we are able to exclude Higgsinos up to 1.8 TeV for binos up to 1.3 TeV.

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.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

La materia ordinaria copre soli pochi punti percentuali della massa-energia totale dell'Universo, che è invece largamente dominata da componenti “oscure”. Il modello standard usato per descriverle è il modello LambdaCDM. Nonostante esso sembri consistente con la maggior parte dei dati attualmente disponibili, presenta alcuni problemi fondamentali che ad oggi restano irrisolti, lasciando spazio per lo studio di modelli cosmologici alternativi. Questa Tesi mira a studiare un modello proposto recentemente, chiamato “Multi-coupled Dark Energy” (McDE), che presenta interazioni modificate rispetto al modello LambdaCDM. In particolare, la Materia Oscura è composta da due diversi tipi di particelle con accoppiamento opposto rispetto ad un campo scalare responsabile dell'Energia Oscura. L'evoluzione del background e delle perturbazioni lineari risultano essere indistinguibili da quelle del modello LambdaCDM. In questa Tesi viene presentata per la prima volta una serie di simulazioni numeriche “zoomed”. Esse presentano diverse regioni con risoluzione differente, centrate su un singolo ammasso di interesse, che permettono di studiare in dettaglio una singola struttura senza aumentare eccessivamente il tempo di calcolo necessario. Un codice chiamato ZInCo, da me appositamente sviluppato per questa Tesi, viene anch'esso presentato per la prima volta. Il codice produce condizioni iniziali adatte a simulazioni cosmologiche, con differenti regioni di risoluzione, indipendenti dal modello cosmologico scelto e che preservano tutte le caratteristiche dello spettro di potenza imposto su di esse. Il codice ZInCo è stato usato per produrre condizioni iniziali per una serie di simulazioni numeriche del modello McDE, le quali per la prima volta mostrano, grazie all'alta risoluzione raggiunta, che l'effetto di segregazione degli ammassi avviene significativamente prima di quanto stimato in precedenza. Inoltre, i profili radiale di densità ottenuti mostrano un appiattimento centrale nelle fasi iniziali della segregazione. Quest'ultimo effetto potrebbe aiutare a risolvere il problema “cusp-core” del modello LambdaCDM e porre limiti ai valori dell'accoppiamento possibili.

The layout of this thesis is the following. In Chapter 2, I introduce some basic elements of modem cosmology and devote special attention to recent observational constraints on cosmological parameters. I also review the theory of gravitational instability, paying particular attention to the theory of collapse of the initial density perturbations. Chapter 3 deals with the issue of hierarchical clustering. I present a Monte Carlo code to generate catalogues of haloes based on the EPS formalism, and then compare its results with numerical simulations. In Chapters 4, 5, and 6 PINOCCHIO code is presented and tested. First, I describe the analytical backbones of this algorithm and then test the code against numerical simulations in order to verify its ability of estimating the statistical properties of the hierarchical clustering of haloes. I will show that PINOCCHIO can also reproduce the numerical experiments to an object-by-object level. In the last two Chapters, I study the evolution of satellites in DM haloes. Chapter 7 derives a simple formula for the decaying time of rigid satellites orbiting in Navarro Frank & White haloes, while Chapter 8 studies the fate of mass loosing satellites which sink in the main DM halo. Conclusions are presented in the last sections of the chapters containing original results (namely, Chapter 3,4,5,6,7,8) and summarized in Chapter 9.

Per quanto la cosmologia osservativa odierna sia in una fase di precisione senza precedenti, con i dati CMB, BAO, e Supernovae Ia che mostrano di essere in accordo con l’attuale modello LCDM, i dati Planck sono in tensione con quelli a basso redshift, provenienti ad esempio dal misurazioni di weak lensing, che puntano verso un tasso più basso di crescita delle strutture. I modelli Dark Scattering qui trattati sono caratterizzati dalla evoluzione di un campo scalare classico con il ruolo di DE, e dalla interazione che le particelle di Materia Oscura (DM) hanno con questo campo. Considerando le particelle DM in moto attraverso il fluido DE, esse osservano un flusso di momento diverso da zero, indice di una forza proporzionale alla sezione d'urto di scattering tra DE e DM. Nel presente lavoro sono stati analizzati dati provenienti da simulazioni cosmologiche N-body DM-only per cinque modelli: due a equazione di stato DE costante, due con equazione di stato dipendente dal tempo, e infine il modello standard LCDM come base di confronto. Le condizioni iniziali sono uguali per tutti i modelli, in modo tale che ogni differenza rilevata nei risultati sia riconducibile agli effetti dei diversi modelli cosmologici. Sono stati ricavati i profili di densità e, per la prima volta su questi dati, i profili di velocità, di un significativo di aloni di materia oscura per ogni cosmologia, divisi in bin di massa e per tre redshift. Viene evidenziato come il termine aggiuntivo di drag nei modelli dark scattering abbia due effetti diversi nella crescita delle strutture. Nel regime lineare, infatti, le particelle DM in infall verso il centro degli ammassi hanno una direzione radiale del moto e l'attrito con il fluido DE le fa rallentare, diminuendo la loro velocità. Quando passano al regime non lineare, acquistano una componente tangenziale di velocità che di fatto fa sì che l'interazione con l'energia oscura provochi una perdita di energia cinetica con conseguente collasso più rapido.

In this work I aim to point out some theoretical issues and caveats in DM search. In the first chapters I review the evidence for DM existence, the DM candidates and the different kinds of DM experimental search. The bulk of the work investigates three different topics. In the first topic, concerning neutrino from the Sun, I show the fact that evaporation does not allow to probe part of the parameter space, in the low mass range. In the second one, I show that, like in the case of the detected positron excess, that could be explained both by DM or by astrophysical source, even a possible excess of antiprotons could suffer from the same kind of degeneracy. In the third part, I consider DM search at collider. I point out some problems about using the EFT low-energy approximation at LHC, arising from the fact that the experimental bounds and the average energy of collisions at LHC are of the same order of magnitude. Afterward, to take this fact into account, I propose a method to rescale experimental bounds, and I review an alternative way of analyzing experimental results, that is using Simplified Models. Finally, I also show which is the part of the parameter space for both Simplified Models and EFT giving the DM the right relic abundance, in the case of thermal freeze-out.

This thesis presents several topics in both standard and non-standard solar models using the Iben Stellar Evolution Code. First, a set of standard solar models are developed using the abundance determination of Grevesse & Noels (1993) and the more recent determination of Asplund et al. (2005a,b). This recent solar photospheric abundance analysis reduces the abundances of heavy elements, most notably C, N, 0, Ne and Ar, by 0.15 to 0.20 dex, lowering the solar Z/X to 0.0165, compared to the previous Grevesse & Noels value of Z/X = 0.0245. A comparison study between these models show evolutions based on newer determinations with reduced heavy-element abundances break the previously excellent agreement between the standard solar model and the helioseismic inferences of sound speed profile, convection zone base radius and surface Y abundance. Multiple approaches taken to reconcile the new abundances with helioseismology are discussed, and models with selective enhancements to diffusion given special attention. The results of all attempts provide an incomplete and unsatisfactory solution. Evolution, helioseismic and g-mode calculations were done in a separate study of nonstandard solar models for spin-dependent interactions with 5 - 20 GeV mass WIMPs in a parameter space loosely constrained by detection experiments. Results for models with 10-40 ::; (O''annV) ::; 10-27 cm3 s-l show that solar modelling can only constrain parameters for \VIMP background densities Px > 103 GeV cm-3 if their annihilation is dominated by scalar interactions; the case for neutralinos. For dark matter annihilating through vector interactions, such as scalar dark matter, the solar model can be used to place constraints on WHviP parameters at a background density of Px ,...., 0.3 GeVcm-3, which is predicted for the Sun.

The modern era of particle physics is driven by experimental anomalies. Experimental efforts have become increasingly diverse and are producing enormous volumes of data. In such a highly data-driven scientific environment theoretical models are necessary to understand this data and to help inform the development of new experimental approaches. In this dissertation I present two significant contributions to this effort relevant to the energy, intensity, and cosmic frontiers of modern particle physics research. Part 1 of this dissertation discusses methods to understand modern dark matter direct detection results. In particular I present an analysis under the hypothesis of inelastic dark matter, which supposes that dark matter must scatter inelastically, i.e. that it must gain or loose mass during a collision with atomic nuclei. This hypothesis is attractive because it can alleviate otherwise contradictory results from a number of dark matter detection facilities. The main conclusion of this work is a presentation of the analytical tools, along with a mathematica package that can be used to run the analysis, and the discovery that there are regions of inelastic dark matter parameter space which are consistent with all current experimental results, and constraints. Part 2 of this dissertation discusses a phenomenon of modern interest called kinetic mixing which allows particles from the standard model to spontaneously transform into particles which experience a new, as of yet undiscovered, force. This phenomenon is relatively common and well motivated theoretically and has motivated significant experimental effort. In this work, I present an analysis of a general case of kinetic mixing, called nonabelian kinetic mixing. This work shows that, In general, kinetic mixing predicts the existence of a new particle and that, under certain conditions, this particle could be detected at modern particle colliders. Furthermore, the mass of this particle is related to the strength of kinetic mixing. This relationship suggests novel ways to constrain kinetic mixing parameter space, and if observed would provide a very striking indication that such a model is realized in nature.

In chapter 1 we introduce some basic elements of modern cosmology, describing the main features of the standard hot big-bang model and the concept of inflation. Special attention is devoted to show that recent observational data are consistent with the theoretical framework. In chapter 2 we review the theory of gravitational instability in an expanding universe. Both the Eulerian and the Lagrangian perturbative approaches to the evolution of density perturbations are discussed in detail. The spherical top-hat model and a series of dynamical approximations are also presented. Chapter 3 deals with scaling solutions to the problem of clustering growth. After a brief review, we present some original results regarding the evolution of the autocorrelation function of the mass density field. In particular, we test the predictions of some empirically calibrated scaling Ansatze against the analytical solutions obtained by using the Zel'dovich approximation. Chapter 4 is devoted to the issue of hierarchical clustering. First, we describe the Press-Schechter theory for the abundance and mass distribution of dark matter haloes, and its excursion-set extension. A new model for the clustering of dark haloes in Lagrangian space is then discussed. In chapter 5 we present an astrophysical application of the Press-Schechter formalisrn. In particular, we investigate the lensing effect of background supernovae due to mass condensations in three popular CDM cosmologies. Our results suggest that it is not inconceivable that new and existing search teams will soon be able to detect magnified supernovae by conducting deep pencil beam surveys. In chapter 6 we review the theory of biased galaxy formation. Both the original motivations that led to its formulation and recent developments are discussed. In chapter 7 we present a new stochastic approach to the clustering evolution of dark matter halos in Eulerian space. Our results clearly point to a characterization of the halo-to-mass biasing as a highly non-linear and non-local process. This chapter contains some of the most important results of this thesis. We devote chapter 8 to compare the predictions of the models introduced in chapters 4, 6 and 7 with N-body simulations. In appendix A we introduce the basic concepts of the theory of random fields, while in appendix B we briefly summarize the main results of classical kinetic theory. The definition of the n-point correlation functions for a population of discrete objects (e.g. galaxies) is also given.

Modern Cosmology offers us a great understanding of the universe with striking precision, made possible by the modern technologies of the newest generations of telescopes. The standard cosmological model, however, is not absent of theoretical problems and open questions. One possibility that has been put forward is the existence of a coupling between dark sectors. The idea of an interaction between the dark components could help physicists understand why we live in an epoch of the universe where dark matter and dark energy are comparable in terms of energy density, which can be regarded as a strange coincidence given that their time evolutions are completely different. Dark matter and dark energy are generally treated as perfect fluids. Interaction is introduced when we allow for a non-zero term in the right-hand side of their individual energy-momentum tensor conservation equations. We proceed with a phenomenological approach to test models of interaction with observations of redshift-space distortions. In a flat universe composed only of these two fluids, we consider separately two forms of interaction, through terms proportional to the densities of both dark energy and dark matter. An analytic expression for the growth rate approximated as f = Omega^gamma, where Omega is the percentage contribution from the dark matter to the energy content of the universe and gamma is the growth index, is derived in terms of the interaction strength and of other parameters of the model in the first case, while for the second model we show that a non-zero interaction cannot be accommodated by the index growth approximation. The successful expressions obtained are then used to compare the predictions with growth of structure observational data in a Markov Chain Monte Carlo code and we find that the current growth data alone cannot impose constraints on the interaction strength due to their large uncertainties. We also employ observations of galaxy clusters to assess their virial state via the modified Layzer-Irvine equation in order to detect signs of an interaction. We obtain measurements of observed virial ratios, interaction strength, rest virial ratio and departure from equilibrium for a set of clusters. A compounded analysis indicates an interaction strength of 0.29^{+2.25}_{-0.40}, compatible with no interaction, but a compounded rest virial ratio of 0.82^{+0.13}_{-0.14}, which means a 2 sigma confidence level detection. Despite this tension, the method produces encouraging results while still leaves room for improvement, possibly by removing the assumption of small departure from equilibrium.
A cosmologia moderna oferece um ótimo entendimento do universo com uma precisão impressionante, possibilitada pelas tecnologias modernas das gerações mais novas de telescópios. O modelo cosmológico padrão, porém, não é livre de problemas do ponto de vista teórico, deixando perguntas ainda sem respostas. Uma possibilidade que tem sido proposta é a existência de um acoplamento entre setores escuros. A ideia de uma interação entre os componentes escuros poderia ajudar os físicos a entender por que vivemos em uma época do universo na qual a matéria escura e a energia escura são comparáveis em termos de densidades de energia, o que pode ser considerado uma estranha coincidência dado que suas evoluções com o tempo são completamente diferentes. Matéria escura e energia escura são geralmente tratadas como fluidos perfeitos. A interação é introduzida ao permitirmos um tensor não nulo no lado direito das equações de conservação dos tensores de energia-momento. Prosseguimos com uma abordagem fenomenológica para testar modelos de interação com observações de distorções no espaço de redshift. Em um universo plano composto apenas por esses dois fluidos, consideramos, separadamente, duas formas de interação, através de termos proporcionais às densidades de energia escura e de matéria escura. Uma expressão analítica para a taxa de crescimento aproximada por f = Omega^gamma, onde Omega é a contribuição percentual da matéria escura para o conteúdo do universo e gamma é o índice de crescimento, é deduzida em termos da interação e de outros parâmetros do modelo no primeiro caso, enquanto para o segundo caso mostramos que uma interação não nula não pode ser acomodada pela aproximação do índice de crescimento. As expressões obtidas são então utilizadas para comparar as previsões com dados observacionais de crescimento de estruturas em um programa para Monte Carlo via cadeias de Markov. Concluímos que tais dados atuais por si só não são capazes de restringir a interação devido às suas grandes incertezas. Utilizamos também observações de aglomerados de galáxias para analisar seus estados viriais através da equação de Layzer-Irvine modificada a fim de detectar sinais de interação. Obtemos medições de taxas viriais observadas, constante de interação, taxa virial de equilíbrio e desvio do equilíbrio para um conjunto de aglomerados. Uma análise combinada indica uma constante de interação 0.29^{+2.25}_{-0.40}, compatível com zero, mas uma taxa virial de equilíbrio combinada de 0.82^{+0.13}_{-0.14}, o que significa uma detecção em um intervalo de confiança de 2 sigma. Apesar desta tensão, o método produz resultados encorajadores enquanto ainda permite melhorias, possivelmente pela remoção da suposição de pequenos desvios do equilíbrio.

Despite the many successes of the current standard model of cosmology on the largest physical scales, it relies on two phenomenologically motivated constituents, cold dark matter and dark energy, which account for approximately 95% of the energy-matter content of the universe. From a more fundamental point of view, however, the introduction of a dark energy (DE) component is theoretically challenging and extremely fine-tuned, despite the many proposals for its dynamics. On the other hand, the concept of cold dark matter (CDM) also suffers from several issues such as the lack of direct experimental detection, the question of its cosmological abundance and problems related to the formation of structure on small scales. A perhaps more natural solution might be that the gravitational interaction genuinely differs from that of general relativity, which expresses itself as either one or even both of the above dark components. Here we consider different possibilities on how to constrain hypothetical modifications to the gravitational sector, focusing on the subset of tensor-vector-scalar (TeVeS) theory as an alternative to CDM on galactic scales and a particular class of chameleon models which aim at explaining the coincidences of DE. Developing an analytic model for nonspherical lenses, we begin our analysis with testing TeVeS against observations of multiple-image systems. We then approach the role of low-density objects such as cosmic filaments in this framework and discuss potentially observable signatures. Along these lines, we also consider the possibility of massive neutrinos in TeVeS theory and outline a general approach for constraining this hypothesis with the help of cluster lenses. This approach is then demonstrated using the cluster lens A2390 with its remarkable straight arc. Presenting a general framework to explore the nonlinear clustering of density perturbations in coupled scalar field models, we then consider a particular chameleon model and highlight the possibility of measurable effects on intermediate scales, i.e. those relevant for galaxy clusters. Finally, we discuss the prospects of applying similar methods in the context of TeVeS and present an ansatz which allows to cast the linear perturbation equations into a more convenient form.

L'obiettivo della Tesi è lo studio del moto dell’ICM in rotazione in ammassi e fare dei test osservativi per i futuri telescopi in banda X, come ATHENA. Nel lavoro realizzato da Bianconi (2013) studiarono la rotazione del gas in ammassi con un potenziale sferico di NFW utilizzando profili di velocità, valutandone gli effetti sull’ellitticità delle isofote X; nella seconda parte il lavoro si focalizzò nello studio di spettri simulati utilizzando le specifiche del calorimetro di Astro-H. Utilizzando il metodo presentato da Ciotti and Bertin abbiamo espanso il potenziale gravitazionale in forma ellissoidale.Abbiamo assunto uno schiacciamento del potenziale di ∼0.4. Abbiamo ricreato potenziali oblati e prolati per verificare come le diverse geometrie avessero effetti sugli osservabili dell’ICM.In particolare abbiamo considerato aloni di dark matter assialsimmetrici con un profilo di NFW e con un rapporto assiale di ∼0.6 e abbiamo confrontato lo schiacciamento delle isofote con i risultati di Lau (2012). Abbiamo misurato uno schiacciamento medio di ~0.13 per quanto riguarda i modelli non rotanti e di ~0.16 per quanto concerne i modelli rotanti, sia nel caso oblato che prolato. L’ultima parte del lavoro presenta uno studio degli spettri X simulati a diversi raggi dal centro degli ammassi dopo che si è convoluta la brillanza con la risposta strumentale dello spettrometro X-IFU di ATHENA per misurare il moto coerente del gas. Abbiamo misurato uno spostamento Doppler della riga a 6.7 keV dell’ordine di ∼5 eV, corrispondente ad una velocità di ~1000 km/s, per i modelli oblati.Nei modelli prolati invece abbiamo trovato uno spostamento del centroide di ∼15 eV, consistente con una velocità superiore a 2400 km/s. Dopo aver valutato lo spostamento della riga abbiamo analizzato l’allargamento dovuto alla dispersione di velocità. Abbiamo quindi trovato che nelle regioni interne si raggiunge un allargamento di 1000 km/s per i modelli prolati mentre per gli oblati di ~300 km/s.

Well motivated theoretical models predict the annihilation of dark matter (DM) into standard model particles, a phenomenon which could be a significant source of photons in the gamma-ray sky. With its unprecedented sensitivity and its broad energy range (20 MeV to more than 300 GeV) the main instrument on board the Fermi satellite, the Large Area Telescope (LAT), might be able to detect an indirect signature of DM annihilations. In this work we revisit several interesting claims of extended dark matter emission made from analyses of Fermi-LAT data: First, based on three years of Fermi Large Area Telescope (LAT) gamma-ray data of the Virgo cluster, evidence for an extended emission associated with dark matter pair annihilation in the bb̄ channel has been reported by Han et al. (arxiv:1201.1003). After an in depth spatial and temporal analysis, we argue that the tentative evidence for a gamma-ray excess from the Virgo cluster is mainly due to the appearance of a population of previously unresolved gamma-ray point sources in the region of interest. These point sources are not part of the LAT second source catalogue (2FGL), but are found to be above the standard detection significance threshold when three or more years of LAT data is included. Second, we confirm the detection of a spatially extended excess of 2-5 GeV gamma rays from the Galactic Center (GC), consistent with the emission expected from annihilating dark matter or an unresolved population of about 10³ milisecond pulsars. However, there are significant uncertainties in the diffuse galactic background at the GC. We have performed a revaluation of these two models for the extended gamma ray source at the GC by accounting for the systematic uncertainties of the Galactic diffuse emission model. We also marginalize over point source and diffuse background parameters in the region of interest. We show that the excess emission is significantly more extended than a point source. We find that the DM (or pulsars population) signal is larger than the systematic errors and therefore proceed to determine the sectors of parameter space that provide an acceptable fit to the data. We found that a population of order a 10³ MSPs with parameters consistent with the average spectral shape of Fermi-LAT measured MSPs was able to fit the GC excess emission. For DM, we found that a pure τ⁺τ⁻ annihilation channel is not a good fit to the data. But a mixture of τ⁻τ⁻ and bb̄ with a (σν) of order the thermal relic value and a DM mass of around 20 to 60 GeV provides an adequate fit. We also consider the possibility that the GeV excess is due to nonthermal bremsstrahlung produced by a population of electrons interacting with neutral gas in molecular clouds. The millisecond pulsars and dark matter alternatives have spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope γ = 1.2. We model the third option with a 20-cm continuum emission Galactic Ridge template. A template based on the HESS residuals is shown to give similar results. The gamma-ray excess is found to be best fit by a combination of the generalized NFW squared template and a Galactic Ridge template. We also find the spectra of each template is not significantly affected in the combined fit and is consistent with previous single template fits. That is, the generalized NFW squared spectrum can be fit by either of order 10³ unresolved MSPs or DM with mass around 30 GeV, a thermal cross section, and mainly annihilating to bb̄ quarks. While the Galactic Ridge continues to have a spectrum consistent with a population of nonthermal electrons whose spectrum also provides a good fit to synchrotron emission measurements. We also show that the current DM fit may be hard to test, even with 10 years of Fermi-LAT data, especially if there is a mixture of DM and MSPs contributing to the signal, in which case the implied DM cross section will be suppressed.

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.

The striking evidence for the existence of dark matter in the Universe implies that there is new physics to be discovered beyond the Standard Model. To identify the nature of this dark matter is a key task for modern astroparticle physics, and a large number of experiments pursuing a range of different search strategies have been developed to solve it. The topic of this thesis is the complementarity of these different experiments and the issue of how to combine the information from different searches independently of experimental and theoretical uncertainties. The first part focuses on the direct detection of dark matter scattering in nuclear recoil detectors, with a special emphasis on the impact of the assumed velocity distribution of Galactic dark matter particles. By converting experimental data to variables that make the astrophysical unknowns explicit, different experiments can be compared without implicit assumptions concerning the dark matter halo. We extend this framework to include annual modulation signals and apply it to recent experimental hints for dark matter, showing that the tension between these results and constraints from other experiments is independent of astrophysical uncertainties. We explore possible ways of ameliorating this tension by changing our assumptions on the properties of dark matter interactions. In this context, we propose a new approach for inferring the properties of the dark matter particle, which does not require any assumptions about the structure of the dark matter halo. A particularly interesting option is to study dark matter particles that couple differently to protons and neutrons (so-called isospin-violating dark matter). Such isospin-violation arises naturally in models where the vector mediator is the gauge boson of a new U(1) that mixes with the Standard Model gauge bosons. In the second part, we first discuss the case where both the Z' and the dark matter particle have a mass of a few GeV and then turn to the case where the Z' is significantly heavier. While the former case is most strongly constrained by precision measurements from LEP and B-factories, the latter scenario can be probed with great sensitivity at the LHC using monojet and monophoton searches, as well as searches for resonances in dijet, dilepton and diboson final states. Finally, we study models of dark matter where loop contributions are important for a comparison of LHC searches and direct detection experiments. This is the case for dark matter interactions with Yukawa-like couplings to quarks and for interactions that lead to spin-dependent or momentum suppressed scattering cross sections at tree level. We find that including the contribution from heavy-quark loops can significantly alter the conclusions obtained from a tree-level analysis.

Numerous astrophysical and cosmological observations support the existence of non-baryonic Dark Matter in the Universe. Its presence is well established at different scales, from galaxies to large scale structures and cosmological scales. However, despite the numerous and independent evidences, the nature of Dark Matter in not yet understood. In this thesis we study the prospect for Dark Matter detection through astrophysical observations.
L'esistenza di Materia Oscura non-barionica è provata da numerose osservazioni astrofisiche e cosmologiche. Tracce della sua presenza si trovano a scale molto diverse, dai sistemi galattici e sub-galattici alle strutture a larga scale e alle scale cosmologiche. Nonostante queste molteplici osservazioni, la natura della Materia Oscura è ancora ignota. In questo lavoro di tesi abbiamo studiato le prospettive per la rivelazione di Materia Oscura attraverso osservazioni astrofisiche.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Na primeira parte deste trabalho, fornecemos a história que constitui a base para a evidência de matéria escura. Também, apresentamos aqui alguns dos candidatos à matéria escura mais estudados. Depois, mostramos as ferramentas necessárias ao entendimento dos cálculos de densidade de relíquia, tais como a base de Relatividade Geral e da cosmologia do universo primordial (termodinâmica do universo primordial, média térmica da seção de choque de aniquilação vezes a velocidade, e as soluções analítica e numérica para a equação de Boltzmann). Finalmente, dentro desta parte de fundamentação, discutimos brevemente alguns dos experimentos de detecção direta e indireta e vínculos impostos por eles sobre a matéria escura. Na segunda parte, analisamos uma extensão, do Modelo Padrão, obtida adicionando-se à simetria de gauge um grupo U(1) local de carga B-L, número bariônico menos número leptônico. Nós mostramos que esta extensão, chamada de modelo B-L, pode conter dois candidatos viáveis à matéria escura e estudamos as condições sobre o espaço de parâmetros do potencial escalar que não só resulta na densidade de relíquia observada, mas também está em acordo com os vínculos provenientes de experimentos de detecção direta
In the ?rst part of this work, we provide the historical background that underlies the evidence of dark matter. Also, we present here some of the most studied dark matter candidates. Later, we show the necessary tools for the understanding of relic density calculation, such as the basics of General Relativity and the early Universe Cosmology (thermodynamics of the early Universe, the thermal average of the annihilation cross section times the velocity, and both the approximated analytical and numerical solutions to the Boltzmann equation). Finally, in this grounding part, we discuss brie?y some of both direct and indirect detection experiments and constraints imposed by them on dark matter. In the second part, we analyze an extension of the Standard Model (SM) obtained by adding to the gauge symmetry a local U(1) group of charge B-L , baryon minus lepton numbers. Weshowthatthisextension,calledB-LModel,cancontaintwoviablecolddark matter candidates and we study the conditions on the space of parameters of the scalar potential that both yields the observed relic density and is in agreement with constraints which come from direct detection experiments

Orientador: Juan Carlos Montero Garcia
Co-orientador: Bruce Lehmann Sánchez Vega
Banca: Adriano Antonio Natale
Banca: Pedro Cunha de Holanda
Resumo: Na primeira parte deste trabalho, fornecemos a história que constitui a base para a evidência de matéria escura. Também, apresentamos aqui alguns dos candidatos à matéria escura mais estudados. Depois, mostramos as ferramentas necessárias ao entendimento dos cálculos de densidade de relíquia, tais como a base de Relatividade Geral e da cosmologia do universo primordial (termodinâmica do universo primordial, média térmica da seção de choque de aniquilação vezes a velocidade, e as soluções analítica e numérica para a equação de Boltzmann). Finalmente, dentro desta parte de fundamentação, discutimos brevemente alguns dos experimentos de detecção direta e indireta e vínculos impostos por eles sobre a matéria escura. Na segunda parte, analisamos uma extensão, do Modelo Padrão, obtida adicionando-se à simetria de gauge um grupo U(1) local de carga B-L, número bariônico menos número leptônico. Nós mostramos que esta extensão, chamada de modelo B-L, pode conter dois candidatos viáveis à matéria escura e estudamos as condições sobre o espaço de parâmetros do potencial escalar que não só resulta na densidade de relíquia observada, mas também está em acordo com os vínculos provenientes de experimentos de detecção direta
Abstract: In the first part of this work, we provide the historical background that underlies the evidence of dark matter. Also, we present here some of the most studied dark matter candidates. Later, we show the necessary tools for the understanding of relic density calculation, such as the basics of General Relativity and the early Universe Cosmology (thermodynamics of the early Universe, the thermal average of the annihilation cross section times the velocity, and both the approximated analytical and numerical solutions to the Boltzmann equation). Finally, in this grounding part, we discuss briefly some of both direct and indirect detection experiments and constraints imposed by them on dark matter. In the second part, we analyze an extension of the Standard Model (SM) obtained by adding to the gauge symmetry a local U(1) group of charge B-L , baryon minus lepton numbers. Weshowthatthisextension,calledB-LModel,cancontaintwoviablecolddark matter candidates and we study the conditions on the space of parameters of the scalar potential that both yields the observed relic density and is in agreement with constraints which come from direct detection experiments
Mestre

De nombreuses observations astrophysiques et cosmologiques indiquent l'existence de Matière Noire non-baryonique dans l'Univers. Sa présence est bien établie à différentes échelles, des galaxies aux structures à grande échelle et aux échelles cosmologiques. Toutefois, malgré ces nombreux indices indépendants, la nature de la matière noire demeure aujourd'hui encore inconnue. Parmi les nombreux candidats proposés, les WIMPs (acronyme de l'anglais Weakly Interacting Massive Particles) sont les plus populaires. Dans cette thèse, nous étudions les perspectives de détection indirect des WIMPs. Nous considerons grandes concentrations de Matière Noire que il peut avoir autour de trous noirs de masse intermédiaire et nous étudions les perspectives de détection des rayons gamma produits par l'annihilation de WIMPs. Nous examinons aussi la recherche indirect de WIMPs dans les flux des rayons cosmiques. Enfin, nous montrons que les annihilations de WIMPs pourraient modifier radicalement l'évolution des premières étoiles
Numerous astrophysical and cosmological observations support the existence of non-baryonic Dark Matter in the Universe. Its presence is well established at different scales, from galaxies to large scale structures and cosmological scales. However, despite the numerous and independent evidences, the nature of Dark Matter in not yet understood. Among the large number of Dark Matter candidates proposed in literature, Weakly Interacting Massive Particles (WIMPs) are the most popular. In this thesis we study the prospect for indirect detection of WIMPs. We first focus on searches of large DM overdensities around Intermediate Mass Black Holes with gamma-ray experiments. We then consider DM searches in the antimatter cosmic-ray fluxes and finally we study the impact of WIMPs annihilations in the evolution of the first stars