We report investigations of physical possibilities beyond the Standard Model, performed in the years between Runs I and II of the Large Hadron Collider (LHC). First, we explore the feasibility of using a hadron collider to unmask hidden sectors by means of a novel signal, the ``monocline". Dilepton production provides the cleanest channel to anticipate a monocline. A compelling sector to seek is dark matter with scalar messengers coupling it to standard fermions. We present current bounds from dilepton spectrum measurements at the LHC and make predictions for sensitivities at Run II of the LHC as well as at a future 100 TeV collider. Second, we corner the space of parameters of supersymmetric frameworks with an appreciable Yukawa coupling between the Higgs fields and a gauge singlet, the so-called Fat Higgs and $\lambda$-SUSY models, in the context of the discovery of the 125 GeV Higgs particle. These models are motivated by their alleviation of the electroweak fine-tuning that supersymmetry breaking entails, via raising the tree-level quartic coupling Higgs boson. Heavy Higgs scalars that couple strongly to the standard Higgs boson induce large radiative corrections to the Higgs quartic coupling, which is crucial to phenomenology; in particular, a very large ratio of the Higgs VEVs ($\tan \beta$), that was previously presumed unfavorable in these models, becomes viable and can be probed by future experiments. In such regions, the most stringent limits come from dark matter constraints on the lightest neutralino. Finally, we place limits on colored scalar production at the LHC in supersymmetric models where gauginos acquire both Dirac and Majorana masses, that we call ``mixed gauginos". While it was known that purely Dirac gluinos were less constrained by LHC searches than their purely Majorana counterparts, we find that the constraints further weaken or strengthen depending on which of the ``mixed" colored fermions acquires a Majorana mass. Also explored are the effects on squark production of turning on Majorana masses for electroweak gauginos. This dissertation consists of previously published and unpublished co-authored material.

Orientador: Nathan Jacob Berkovits / Banca: Victor de Oliveira Rivelles / Banca: Nelson Ricardo de Freitas Braga / Banca: Yuri Aisaka / Banca: Dáfni Fernanda Zenedin Marchioro / Resumo: Nesta tese, mostramos o cálculo da função de partição dos espinores puros. O cálculo será executado de dois modos diferentes usando o método de fantasma-para-fantasma (até o décimo segundo nível massivo) e usando o método do ponto fixo (até o quinto nível massivo). Após incluir a contribuição das variáveis do setor da matéria ('qui POT. m, 'teta POT. alfa', 'rô IND. alfa'), nós derivamos o espectro massivo da supercorda aberta. Embora os espinores puros sejam variáveis bosônicas, a função de partição dos espinores puros contém estados fermiônicos os quais começam aparecer a partir do segundo nível massivo. Estes estados fermiônicos vêm de funções que não são bem definidas globalmente no espaço dos espinores puros, e estão relacionados ao fantasma b no formalismo de spinores puros para a supercorda / Abstract: In this thesis, we have calculated the partition function of pure spinors. The computation is performed by using two different methods, namely ghosts-for-ghosts (up to the twelth mass-level) and fixed point (up to the fifth mass-level) techniques. After adding the contribution from the ('qui POT. m, 'teta POT. alfa', 'rô IND. alfa') matter variables, we reproduce the massive open superstring spectrum. Even though pure spinor variables are bosonic, the pure spinor partition function contains fermionic states which first appear at the second mass-level. These fermionic states come from functions which are not globally defined in pure spinor space, and are related to the b ghost in the pure spinor formalism for the superstring / Doutor

We investigate several aspects of four dimensional supersymmetric gauge theories with the minimal amount of supercharges both from the theoretical and the phenomenological view point. On the theoretical side we investigate the behavior of two-point correlators of short multiplets for vacua that spontaneously break supersymmetry. The main goal is to build up an exhaustive description of the supersymmetry breaking dynamics that it is easily extendable to strongly coupled gauge theories. When strong coupling is involved we study the behavior of two-point correlators by means of AdS/CFT techniques building up models of strongly coupled hidden sectors that break supersymmetry and can be described holographically by gauged supegravity in five dimensions. These hidden sectors have also some phenomenological interest in particle physics beyond the Standard Model since they can be used as supersymmetry-breaking sectors in models where the breaking of supersymmetry is mediated by gauge interactions. On the more phenomenological side we study how the Higgs mass requirements constraints gauge mediation models and what could be possible interesting signatures of these scenarios at LHC. / Doctorat en sciences, Spécialisation physique / info:eu-repo/semantics/nonPublished

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By formulating the six dimensional (0,2) superconformal field theory X[j] on a Riemann surface decorated with certain codimension two defects, a multitude of four dimensional N=2 supersymmetric field theories can be constructed. In this dissertation, various aspects of this construction are investigated in detail for j=A,D,E. This includes, in particular, an exposition of the various partial descriptions of the codimension two defects that become available under dimensional reductions and the relationships between them. Also investigated is a particular observable of this class of four dimensional theories, namely the partition function on the four sphere and its relationship to correlation functions in a class of two dimensional non-rational conformal field theories called Toda theories. It is pointed out that the scale factor that captures the Euler anomaly of the four dimensional theory has an interpretation in the two dimensional language, thereby adding one of the basic observables of the 4d theory to the 4d/2d dictionary. / text

In this thesis it will be shown that the hydrogen atom has a SU(2) × SU(2) symmetry generated by the quantum mechanical angular momentum and Runge-Lenz vector operators. Additionally, the hydrogenic atom will be studied with supersymmetric methods to identify a supersymmetry that relates different such systems. This thesis is intended to present the material in a manner accessible to people without background in Lie groups and supersymmetry, as well as fill in some calculations between steps that are not spelt out in the litterature.

The Large Hadron Collider at CERN completed its first data-taking phase in 2013, after three years of remarkable performance. The high-energy proton-proton collisions recorded by the ATLAS experiment provide a gateway to the world of subatomic particles. This thesis presents two analyses of the full 8 TeV dataset taken by ATLAS, inspired by two of the major physics goals of the experiment. The first analysis is a search for new phenomena that could explain the nature of Dark Matter and solve the hierarchy problem. In particular, the search is optimised to look for heavy supersymmetric particles decaying to large numbers (7 to ≥10) of jets. The events are further classified according to the number of jets identified as originating from a b quark. No evidence is found for physics beyond the Standard Model, so the results are interpreted in terms of exclusion limits on various simplified supersymmetry-inspired models where gluinos are pair produced, as well as a mSUGRA/CMSSM model. The main background to the search is due to multi-jet production via the strong force. This motivates the second analysis presented in this thesis, which is a measurement of the cross section of four-jet events. The measurement is performed differentially in a series of variables which describe the kinematics and spatial configuration of the events. The results are compared to existing theoretical predictions.

Under the umbrella of Theoretical Physics, progress in ‘Beyond the Standard Model’ (BSM) physics proceeds broadly along two main avenues of investigation. The first is concerned with constructing theories that attempt to explain observations, or address theoretical problems, which cannot be explained within the tremendously successful Standard Model (SM) of particle physics. The second involves looking for new ways to observe or test BSM physics, and such tests are usually developed with current experimental hints, or attractive theoretical models, in mind. This thesis contains material which falls under both approaches. Part I is concerned with Supersymmetry (SUSY). We review the basics of SUSY, and the current state of this field, and then present a novel model for SUSY at the TeV scale. This model has a Higgs sector similar to the SM and possesses a continuous U(1)_R symmetry, dramatically suppressing contributions to flavour-changing neutral currents, which can be problematic in SUSY models. After this we demonstrate that if more than one SUSY-breaking sector is present then this could lead to a rich spectrum of states with mass roughly twice the gravitino mass. In particular, if SUSY-breaking in a hidden sector arises dynamically then multiple ‘Goldstini’ and ‘Modulini’ states can arise, which couple to visible sector fields via the ‘Goldstino Portal’. We also demonstrate a new phenomenon which can occur in the context of multiple hidden sectors. If one sector breaks SUSY then this can ‘stimulate’ other sectors into also breaking SUSY, even if they are incapable of doing so on their own. Part II focusses on the matter in our Universe. We review our current understand- ing of how the visible matter in our Universe came into existence, and our current understanding of the nature of dark matter (DM). Following this we describe how DM could potentially be indirectly observed through its effects on cold white dwarf stars. Alternatively, if DM were detected by independent means, then observed cold white dwarfs could be used to place limits on the DM density in globular clusters, giving clues as to how these clusters of stars formed. We then present a new model for the co-generation of both the visible and dark matter in our Universe. This proceeds by generating a particle anti-particle asymmetry in the dark sector, which is then shared with the visible sector. This model predicts the existence of a light, m ≲ 5 eV, scalar particle which derivatively couples to DM, and provides a final state for the symmetric DM component to annihilate away into. Work completed during the period of this D.Phil is contained in [1–8], however only material in [3–6, 8] is presented in this thesis.

This thesis studies the geometry of hyperbolic monopoles using supersymmetry in four and six dimensions. On the one hand, we show that starting with a four dimensional supersymmetric Yang-Mills theory provides the necessary information to study the geometry of the complex moduli space of hyperbolic monopoles. On the other hand, we require to start with a six dimensional supersymmetric Yang-Mills theory to study the geometry of the real moduli space of hyperbolic monopoles. In chapter two, we construct an off-shell supersymmetric Yang-Mills-Higgs theory with complex fields on three-dimensional hyperbolic space starting from an on-shell supersymmetric Yang-Mills theory on four-dimensional Euclidean space. We, then, show that hyperbolic monopoles coincide precisely with the configurations that preserve one half of the supersymmetry. In chapter three, we explore the geometry of the moduli space of hyperbolic monopoles using the low energy linearization of the field equations. We find that the complexified tangent bundle to the hyperbolic moduli space has a 2-sphere worth of integrable structures that act complex linearly and behave like unit imaginary quaternions. Moreover, we show that these complex structures are parallel with respect to the Obata connection, which implies that the geometry of the complexified moduli space of hyperbolic monopoles is hypercomplex. We also show, as a requirement of analysing the geometry, that there is a one-to-one correspondence between the number of solutions of the linearized Bogomol’nyi equation on hyperbolic space and the number of solutions of the Dirac equation in the presence of hyperbolic monopole. In chapter four and five, we shift the focus to supersymmetric Yang-Mills theories in six dimensional Minkowskian spacetime. Via dimensional reduction we construct a supersymmetric Yang-Mills Higgs theory on R3 with real fields which we then promote to H3. Under certain supersymmetric constraints, we show that hyperbolic monopoles configurations of this theory preserve, again, one half of the supersymmetry. Then, through investigating the geometry of the moduli space we showthat the moduli space is described by real coordinate functions (zero modes), and we construct two sets of 2-sphere of real complex structures that act linearly on the tangent bundle of the moduli space, but don’t behave like unit quaternions. This result coincides with the result of Bielawski and Schwachhöfer, who called this new type of geometry pluricomplex geometry. Finally, we show that in the limiting case, when the radius of curvature H3 is set to infinity, the geometry becomes hyperkähler which is the geometry of the moduli space of Euclidian monopoles.