Orientador: Prof. Dr. Alysson Fábio Ferrari / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2016. / Operadores contendo derivadas superiores não estão incluídos no Modelo Padrão Estendido (SME) e podem ter relevância na busca por uma teoria que opere na escala de Planck. Nessa tese de doutorado investigamos algumas consequências físicas no regime de baixas energias devido a violação de Lorentz (Lorentz violation, ou LV) gerada por operadores desse tipo. Começamos com um modelo constituído pelo campo fermiônico carregado e massivo , pelo campo do fóton A e pelo campo do tipo áxion (ALP ou axion-like-particle) . A LV aparece através dos acoplamentos não mínimos Fd e 5=b , onde d e b são os vetores constantes responsáveis pela introdução da LV. Assumimos que o campo fermiônico tem massa muito grande, e integramos a ação efetiva no campo do férmion, obtendo então como correção quântica de uma laço uma interação efetiva a baixa energia entre o campo do fóton e o campo do ALP, que resulta ser do mesmo tipo de interação que tem sido investigado em pesquisas experimentais atuais. Em seguida, estudamos outras consequências da interação Fd por meio correções quânticas de um laço, agora exclusivamente no setor de fóton. Mostramos que tal interação LV é responsável por gerar na ação efetiva operadores LV com derivadas superiores. Dentre as correções quânticas geradas consideramos a correção até primeira ordem no parâmetro LV d, juntamente com as correções não lineares de mais baixa ordem, e investigamos efeitos da LV na propagação de ondas eletromagnéticas em uma região contendo um campo magnético forte e constante. Por fim investigamos consequências físicas adicionais da interação Fd por meio das interações entre fontes externas intermediadas pelo campo eletromagnético, onde discutimos os principais fenômenos físicos que emergem dessa teoria e que não são contemplados na teoria de Maxwell usual. / Higher derivatives operators are not included in the Standard Model Extension (SME) and they can have relevance in the search by a theory which operates in the Planck energy scale. In this PhD thesis we investigate some physical consequences in the low energy regime due to LV which was generated by this kind of operators. We start with a model in the high energy regime that is constituted by the charged massive fermionic field , by the photon field A and by the axion-like-particle (ALP) field . The LV appear in our model due to the two couplings Fd and 5=b , where d and b are the constant vectors responsible for introducing the LV. We assume the fermion mass to be very high and we integrate the effective action in the fermion field, obtaining as one-loop quantum correction an effective interaction in the low energy regime between the photon field and ALP field, which we show to be of the same form as the one studied in current experimental searches. Then, we study other physical consequences of the interaction Fd through one-loop quantum corrections in the pure photon sector. We show that such LV interaction generates in the effective action Lorentz violating higher derivatives operators. Among the generated quantum corrections we consider the ones of the first order in the LV parameter d; together with the lowest order non-linear corrections, and we investigate the effects of the LV in the electromagnetic wave propagation in a region with a strong, constant magnetic field. To finish, we investigate additional physical consequences of the interaction Fd through interactions between external sources intermediated by the electromagnetic field, where we discuss the main physical phenomena that emerge of this theory which have no counterpart in Maxwell theory.

The lack of direct evidence for physics beyond the SM at the LHC has led some to reevaluate the need for such physics to solve the hierarchy problem. Instead, the notion that the SM, or something like it, is valid up to the Planck scale and that technical naturalness is sufficient for solving the hierarchy problem has been suggested. This thesis examines minimal extensions of the SM that address its phenomenological and theoretical shortcomings while avoiding new physics between the electroweak and Planck scales that introduces a hierarchy problem. This thesis first studies two issues with the vMSM - an extension of the SM by three right-handed neutrinos - and their possible solutions. The first issue is the tension between dark matter production in the nuMSM and constraints from the Lyman-alpha forest data. To avoid this tension, the vMSM is extended by a Higgs singlet Φ and neutrino dark matter is produced through the decays of Φ rather than through left-right neutrino mixing. It is shown that the hierarchical parameters of this model can arise from symmetries broken at or near the Planck scale for two specific examples: one in which Φ stabilizes the electroweak vacuum and one in which Φ is a light inflaton. The second issue pertains to Higgs ξ-inflation. In the vMSM, a large non-minimal coupling ξ of the Higgs to gravity gives inflation but leads to a possible violation of perturbative unitarity below the inflationary scale. A study of Higgs ξ-inflation with M_h ≃ 125-126 GeV, for which the Higgs self-coupling λ runs to small values near the Planck scale, is carried out. It is shown that small λ can significantly reduce ξ required for inflation, but ξ cannot be small enough to address the possible unitarity issue. For small λ, a new region of Higgs ξ-inflation with a large tensor-to-scalar ratio r that is consistent with BICEP2 is discovered. This thesis then studies the technical naturalness and cosmology of a model that addresses the strong CP problem. It is shown that a classically scale invariant DFSZ invisible aξon model with a Peccei-Quinn scalar S, whose couplings to the SM are ultra-weak, can solve the strong CP problem and generate electroweak symmetry breaking via the Coleman-Weinberg mechanism. The ultra-weak couplings of S are natural due to an underlying approξmate shift symmetry. The model contains a light pseudo-Goldstone dilaton that can be consistent with cosmological bounds while the aξon can be the dark matter of the universe. Finally, a summary of the thesis is presented and future research topics are suggested.

In this thesis I describe the development of a compact camera for ground-based multi TeV gamma-ray astronomy, using the Imaging Atmospheric Cherenkov Telescope (IACT) technique. The camera is based on multi-anode photomultipliers (MAPM) and is designed for use on the Gamma Cherenkov Telescope (GCT), which is proposed to be part of the Small Size Telescope (SST) array of the Cherenkov Telescope Array (CTA). GCT achieves high performance with a compact and cost efficient design via a Schwarzschild-Couder (SC) dual-mirror optical system. The GCT optical design allows the use of a compact camera of diameter roughly 0.5 m. The curved focal plane is equipped with 32 tiles of 64-pixels MAPM for a total of 2048 pixels of ~0.2° angular size, resulting in a field of view of ~9°. The GCT camera is designed to record the flashes of Cherenkov light from electromagnetic cascades, which last only a few tens of nanoseconds. I give a detailed description of the design, the challenges encountered during testing in the lab, and the performance of the most critical components. I give details on the custom front-end electronics modules that provide the required fast electronics, facilitating sampling and digitization, as well as first level of triggering. The camera-level triggering system is a custom backplane, developed to reject spurious triggers on the night sky background, which typically is of the order of few tens of millions of photons per pixel per second. This is to be compared with the rate of the astrophysical signal, which is of the order of few hundreds of events per second at the relevant energies. Additionally I provide a detailed description of all the software needed for the data acquisition and control of the camera, from the very low level drivers to high level and user friendly processes. I follow the commissioning of the camera, from the individual core components to the integration of the system. I then describe the integration of the camera on the GCT prototype telescope structure, and the achievement of "first light", validating for the first time the full proof-of-concept of an IACT with SC optics. I also report a study I performed on expectations for an extragalactic survey for blazars with CTA. The cumulative source count distribution of blazars is presented, including implications from two different phenomena: axion-like particle (ALP) to gamma-ray oscillations in the intergalactic magnetic field, and secondary gamma rays from hadronic origins. I conclude that a shallow and wide survey will provide the best science return for CTA, that the impact of ALP is modest and that the secondary mechanism of gamma-ray production would allow detection of blazars up to redshift of 1 in the multi-TeV energy band.

Orientador: Prof. Dr. Marcelo Augusto Leigui de Oliveira / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, Santo André, 2018. / O objetivo deste trabalho é discutir a distorção do fluxo de raios gama de altas energias (250 GeV ¿ 25 TeV) devido a processos de atenuação desde a fonte até sua chegada na Via Lactea. Entre esses processos estão a produção de pares pela interação com a radiação cósmica de fundo, principalmente EBL, e a oscilação de fótons em bosons pseudoescalares leves, chamados de partículas tipo áxion (ALPs). Também é discutido como será o sinal do fluxo detectado pelo Cherenkov Telescope Array, explicitando suas especificações técnicas e principais melhorias em relação aos detectores atuais, o que nos levará a uma nova geração de telescópios de raios gama. / The purpose of this research is to discuss the distortion of VHE gamma-ray flux (250 GeV - 25 TeV) due to attenuation processes along its path from the source to our galaxy, namely: pair production as a result of the interaction with the background cosmic radiation, especially EBL, and gamma-ray mix with a light pseudoescalar fundamental boson called axion-like particle (ALP). It is also discussed how this signal should appear at Cherenkov Telescope Array, emphasizing its technical specifications and major improvements over current IACTs, which will lead us to a new generation of gamma-ray telescopes.

<p>The ability of the Mu2e experiment to probe, or discover BSM physics in direct CLFV μ+ and π+ decay modes is estimated.</p>

Axionartige Teilchen sind pseudoscalare Teilchen welche in Theorien jenseits des Standardmodells vorhergesagt werden. Falls ein axionartiges Teilchen innerhalb eines kosmischen magnetischen Felds gebildet wird, wird dieses nicht durch das Hintergrundlicht absorbiert. Daher kann es kosmische Distanzen überbrücken bevor es wieder in ein Photon zurück oszilliert. Dieser Effekt erhöht die Reichweite der Gammastrahlung im Universum. Im Rahmen dieser Dissertation werden Daten des Fermi Large Area Telescopes, aufgenommen über eine Zeitraum von sechs Jahren, systematisch analysiert. Hierbei wird nach axionartigen Teilchen mit Hilfe von Transparenzeffekten des Universums gesucht. In diesem Zusammenhang werden verschiedene Modelle des extragalaktischen Hintergrundlichts mit und ohne Berücksichtigung axionartiger Teilchen verglichen. Hierfür werden Likelihood-Funktionen für das höchst energetische Photon verschiedener entfernter Quelle kombiniert. Diese sind aktive galaktische Kerne mit einer Rotverschiebung z ≥0.1 des Second Catalog of Hard Fermi-LAT Sources. Unter den Annahmen einer intergalaktischen magnetischen Feldstärke von B = 1 nG und einer Kohärenzlänge von s = 1 Mpc wurde keine Veränderungen der Transparenz durch axionähnliche Teilchen nachgewiesen. Für eine Masse eines axionartigen Teilchens mit m≅ 3.0 neV wird eine Photonen-Axion Kopplungskonstante über 10(^11) GeV(^−1) ausgeschlossen. / Axion-like particles, pseudo-scalar particles that arise in theories beyond the Standard Model, mix with photons in the presence of magnetic fields. If an axion-like particle is produced within a cosmic magnetic field, it evades extragalactic background light absorption and thus it can survive cosmological distances until oscillating back into a photon. This leads to an increased transparency of the Universe to gamma rays. In the scope of this thesis, we search for transparency effects compatible with the existence of axion-like particles with six years of data from the Fermi Large Area Telescope. We derive and combine the likelihoods of the highest-energy photon events from a sample of hard distant sources, in order to compare models that include axion-like particles and models with only extragalactic background light. The sources are active galactic nuclei from the Second Catalog of Hard Fermi sources at redshift z≥0.1. For values of the intergalactic magnetic field strength B = 1 nG and coherence length s = 1 Mpc, we find no evidence for a modified transparency induced by axion-like particles and therefore we set upper limits. We exclude photon-axion coupling constants above 10(^11) GeV(^−1) for axion masses m≅ 3.0 neV.

This thesis uses theoretical studies, and numerical simulations to provide results of the experimental reach to detect the QCD axion as dark matter in a Non-standard cosmological background. Assuming that the QCD axion constitutes the full CDM abundance of the universe, this thesis elaborates on its potential detection from experimental setups for the mass window of the axion. The set of results that is obtained here are the relic CDM energy density of axions produced by the vacuum realignment mechanism and the CDM energy density of axions produced from the decay of a network of cosmic strings. This thesis provides results regarding the possibility to detect a primordial gravitational wave relic, which is possible within some favorable cosmological scenarios for the background.

Ένα από τα μεγαλύτερα θεωρητικά κατασκευάσματα της φυσικής είναι αυτό της σκοτεινής ύλης. Στην παρούσα μεταπτυχιακή διπλωματική εργασία αναλύονται οι λόγοι για τους οποίους πιστεύουμε στην ύπαρξη της σκοτεινής ύλης, τα σωματίδια και γενικά τα αντικείμενα που μπορεί να την απαρτίζουν, η σκοτεινή ενέργεια και οι μορφές της και τέλος εναλλακτικές προτάσεις. / One of the most important theoretical creations of physics is dark matter. In this master thesis we describe the reasons we believe in the existence of dark matter, the particles and the objects that consists dark matter, dark energy and finally alternative theories.