Probing the Beyond the Standard Model Higgs Sector using the ATLAS Detector

A Higgs boson with a measured mass of 125 GeV has been observed by both the ATLAS and CMS experiments and found to be compatible with the predictions from the Standard Model (SM). The now consolidated Higgs sector has become a topic of considerable study as a potential portal to new physics. Several models beyond the SM (BSM) exist with non-trivial Higgs sectors and predict the existence of additional Higgs bosons yet to be observed. One such type of model is the Two-Higgs-Doublet-Model (2HDM) which extends the SM Higgs sector in a minimal way, while another type which considers supersymmetry is the Minimal Supersymmetric Standard Model (MSSM). The implications of both models are considered in the thesis. This thesis presents two searches for additional Higgs bosons predicted by BSM models. One search is for heavy neutral Higgs bosons decaying to a pair of tau leptons. The second search is for charged Higgs bosons decaying to a tau lepton and a neutrino. No significant excess is observed in either analysis and regions of the parameter space of the MSSM are excluded. This thesis also presents a reinterpretation of the measurement of the 125 GeV Higgs boson cross-section in the context of the 2HDMs and MSSM. The measured 125 GeV Higgs boson cross-sections are found to be compatible with the predictions of the SM, and are used to constrain the 2HDM and MSSM parameter space. Results from the direct searches, in terms of model-independent cross-section limits, and the 125 GeV Higgs boson cross-section measurements are shown to provide complementary constraints on the MSSM parameter space

Statistical mechanics and the description of the early universe II. Principle of detailed balance and primordial 4He formation

If the universe is slightly non-extensive, and the distribution functions are not exactly given by those of Boltzmann-Gibbs, the primordial production of light elements will be non-trivially modified. In particular, the principle of detailed balance (PDB), of fundamental importance in the standard analytical analysis, is no longer valid, and a non-extensive correction appears. This correction is computed and its influence is studied and compared with previous works, where, even when the universe was considered as an slightly non-extensive system, the PDB was assumed valid. We analytically track the formation of Helium and Deuterium, and study the kind of deviation one could expect from the standard regime. The correction to the capture time, the moment in which Deuterium can no longer be substantially photo-disintegrated, is also presented. This allows us to take into account the process of the free decay of neutrons, which was absent in all previous treatments of the topic. We show that even when considering a first (linear) order correction in the quantum distribution functions, the final output on the primordial nucleosynthesis yields cannot be reduced to a linear correction in the abundances. We finally obtain new bounds upon the non-extensive parameter, both comparing the range of physical viability of the theory, and using the latest observational data.Comment: 24 pages, to appear in Physica A (2001

Non-extensivity Effects and the Highest Energy Cosmic Ray Affair

Recent measurements of the cosmic microwave background confirm that it is described by a Planckian distribution with high precision. It is non-extensivity bounded to be less than some parts in $10^5$, or to some parts in $10^4$ at most. This deviation may appear minuscule, but may have a non-negligible effect on a particle propagating through this background over the course of millions of years. In this paper we analyze the possible influence of such a slight deviation upon the propagation of nuclei and protons of ultra-high energy. These particles interact via photopion and photodisintegration processes which we examine taking into account a slight non-extensive background. We show that such a deviation does not exhibit a significant difference in the energy attenuation length of extremely high energy cosmic rays.Comment: Revised version, improvements per referee's suggestion

Precision cosmology as a test for statistics

We compute the shift in the epoch of matter-radiation equality due to the possible existence of a different statistical (non-extensive) background. The shift is mainly caused by a different neutrino-photon temperature ratio. We then consider the prospects to use future large galaxy surveys and cosmic microwave background measurements to constrain the degree of non-extensivity of the universe.Comment: to appear in Physica

Discos regulares como fuentes de la métrica de Kerr

Se muestra cómo mediante una conveniente elección para la topología de la variedad se pueden construir, usando el formalismo de superficies singulares que resulten fuentes de la métrica de Kerr. Se analiza físicamente el tensor superficial energía-momento y se calculan explícitamente las integrales invariantes asociadas con las simetrías del sistema. Se obtiene que la masa y el momento angular de los distintos discos son m y a, respectivamente siendo a el parámetro de rotación.Asociación Argentina de Astronomí

Low temperature specific heat of glasses: a non-extensive approach

Specific heat is calculated using Tsallis statistics. It is observed that it is possible to explain some low temperature specific heat properties of glasses using non-extensive approach. A similarity between temperature dependence of non-extensive specific heat and fractal specific heat is also discussed.Comment: 5 pages, 4 figure

Argentine South Africans ways of speaking about social responsibility in South Africa

A research report submitted to the Faculty of Humanities, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Arts (Diversity Studies). March 2014Despite the end of apartheid, South Africa remains a grossly unequal society. This has meant that the current social order must again be challenged. One of the tasks faced in post-apartheid South Africa is the philosophical and moral interrogation of white privilege. This research investigates the ways of speaking of Argentine immigrants living in South Africa. Semi-structured interviews were conducted and analysed by making use of Laclau and Mouffe’s discourse theory as well as Melissa Steyn’s characteristics of “white talk”. It was found that Argentine immigrants living in South Africa aligned themselves with the ways of speaking of white South Africans. These are largely informed by and embedded in Eurocentric discourses; in particular liberal ideology. In line with the agenda of Critical Whiteness studies, this positionality was exposed and theoretically interrogated. Keywords: whiteness, immigrants, discourse, Laclau and Mouffe discourse theory, white talk, racism, identity, liberalis

Structure of Spinning Particle Suggested by Gravity, Supergravity and Low Energy String Theory

The structure of spinning particle suggested by the rotating Kerr-Newman (black hole) solution, super-Kerr-Newman solution and the Kerr-Sen solution to low energy string theory is considered. Main peculiarities of the Kerr spinning particle are discussed: a vortex of twisting principal null congruence, singular ring and the Kerr source representing a rotating relativistic disk of the Compton size. A few stringy structures can be found in the real and complex Kerr geometry. Low-energy string theory predicts the existence of a heterotic string placed on the sharp boundary of this disk. The obtained recently supergeneralization of the Kerr-Newman solution suggests the existence of extra axial singular line and fermionic traveling waves concentrating near these singularities. We discuss briefly a possibility of experimental test of these predictions.Comment: Latex, 8 pages, talk at the International Workshop Spin'99, Prague, 5-11 September, 199

Relativistic dynamics of cylindrical shells of counter-rotating particles

Although infinite cylinders are not astrophysical entities, it is possible to learn a great deal about the basic qualitative features of generation of gravitational waves and the behavior of the matter conforming such shells in the limits of very small radius. We describe the analytical model using kinetic theory for the matter and the junction conditions through the shell to obtain its equation of motion. The nature of the static solutions are analyzed, both for a single shell as well as for two concentric shells. In this second case, for a time dependent external shell, we integrate numerically the equation of motion for several values of the constants of the system. Also, a brief description in terms of the Komar mass is given to account for the gravitational wave energy emitted by the system.Comment: 19 pages, 8 figure