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We study the correspondence between certain supersymmetric gauge theories and their dual supergravity descriptions. Using low-energy brane probes of the super-gravity geometries we find moduli spaces of vacua, as expected from considering the dual gauge theories. The metrics on these spaces can be put into a form consistent with field theory expectations. This provides a non-trivial check on the supergravity solutions, in addition to strong-coupling predictions for the gauge theories. In the case of N = 2 supersymmetric gauge theory, proposed supergravity duals have previously been shown, using brane probe techniques, to display the 'enhangon mechanism'. In particular, the supergravity geometries correctly reproduce the per-turbative behaviour of the gauge theory. We calculate exact non-perturbative results at low-energies using the method of Seiberg & Witten. These correctly reproduce the perturbative results in the supergravity limit, but also make predictions for when the supergravity approximation is not valid. Finally, we study the Penrose limit of a geometry that is dual to a known N= 1 superconformal gauge theory. The resulting spacetime is a new plane-wave solution with constant three-form fluxes. We quantize type IIB superstrings on this background using the Green-Schwarz formalism. We find the spectrum of string excitations and discover that it is particularly simple, due to the specific form of the plane-wave background. Using the gauge theory/gravity duality, we make predictions (beyond the supergravity approximation) for gauge theory quantities in the corresponding limit.

We investigate the possibility of identifying In(l/x) dynamics from studies of the final state in electron-proton deep inelastic scattering (DIS) in the small x region of the HERA collider at DESY. Motivated by recent observations at HERA we consider again the measurement of DIS events containing an identified forward jet as proposed by Mueller. We find that the shape of the x distribution of the data is described well by a prediction based on In(l/x) dynamics. Since forward jets are difficult to identify and measure accurately in the experiments we suggest the study of deep inelastic events containing an energetic isolated photon. We quantify the enhancement arising from the leading In(l/x) gluon emissions with a view to using such events to identify the underlying dynamics in the small x regime at HERA. To overcome the small event rate of jet + γ we propose that the forward jet may alternatively be identified through a single energetic decay product, the π . We investigate the feasibility of utilizing these deep inelastic + forward π events as an indicator of the small x dynamics. Motivated by this study the HI collaboration recently performed a DIS + π measurement. Therefore we update our BFKL prediction imposing the HI cuts in the calculation. We fix the normalisation by comparing with HERA data for DIS + jet. Finally we study the transverse momentum (pr) spectrum of charged particles produced in DIS at small Bjorken x in the central region between the current jet and the proton remnants. Again we normalize the BFKL prediction by comparing with the H1 DIS + jet data. We calculate the spectrum at large pr with the BFKL ln(l/x) resummation included and then repeat the calculation with it omitted. We find that data favour the former.

Whilst the atmosphere places a limit on the successful applications of many branches of astronomy, it becomes an invaluable tool for the detection of very high energy γ-rays. This thesis is concerned with reducing the systematic uncertainties inherent to using the atmosphere as a detector of very high energy radiation. The interaction processes important to high energy particles are met in the first chapter. The second chapter explores how these interaction processes are responsible for generating observable Cerenkov radiation that can be detected by ground based telescopes. A description of one of these atmospheric Cerenkov telescopes, the University of Durham Mark 6 telescope, is given in chapter 3. A timing analysis was performed on data obtained with this telescope of the high mass X-ray binary Centaurus X-3 and the findings are given in chapter 5. The result of the test for orbital modulation of the VHE γ-ray signal has implications for the possible site of VHE γ-ray emission in this system and for the analysis strategy required to test for modulation of the VHE signal at the pulsar period. One of the findings of the timing analysis was a need for more accurate flux estimates and spectral energy measurements of the VHE γ-ray signal, which requires a greater understanding of the systematic errors inherent to the atmospheric Cerenkov technique. The effective collecting area of a Cerenkov telescope is related to the generation and attenuation of Cerenkov photons in the atmosphere. Uncertainties in the magnitude of the effective area result in errors in the deduced flux, whilst uncertainties in the function of effective area with energy result in errors of the spectral slope determined for any source. By using an inappropriate model for the atmosphere in simulations of atmospheric Cerenkov telescopes a systematic error can be introduced into calculations of the effective area. Chapter 6 compares the effective areas obtained from several model atmosphere types, including a contemporary model of the conditions at the Mark 6 site from data taken with atmospheric monitoring equipment employed in the Mark 6 operations. The findings from this work are then all drawn together in the final chapter, along with a discussion of the future atmospheric monitoring work that will go in to the next generation of atmospheric Cerenkov telescope installations.

Esta tese tem como objetivo apresentar e discutir resultados de um estudo sobre os fenômenos de polarização de híperons e de anti-híperons em processos inclusivos resultantes de interações próton-núcleo e altas energias (centenas de GeV). É proposto um modelo que acreditamos ser o principal responsável pela polarização de anti-híperons em tais processos. A polarização é resultante das interações finais entre os anti-híperons e outras partículas produzidas no processo (que na sua maioria são píons). O modelo baseia-se então em dois elementos: as interações píon-híperon a baixas energias (que estudamos através da lagrangianas efetivas) e das flutuações estatísticas do meio em expansão. O estudo deste meio baseia-se no modelo hidrodinâmico, que considera a formação de matéria hadronica quente durante tais colisões. Os resultados estão em bom acordo com os dados experimentais e conseguem explicar pela primeira vez a polarização de anti-híperons. / We present and discuss in this thesís results of a study on the hyperon and antihyperon polarization phenomena in high-energy (hundreds of GeV) proton-nudeus inclusive reactions. We propose a model that we believe is the main source of the anti-hyperon polarization in these processes. The polarization is originated by the final-state interactions between the antí-hyperons and other produced particles in these collisions (predominantly píons) and based on two elements: the low-energy pion-hyperon interaction (descriebed by effective lagrangians) and the statistical fluctuations plus expansion of the background matter. The results agree quite well wíth the experimental data and gíve for the first time a convencing explanatíon of the anti-hyperon polarization.

<p> A novel electret fabrication method has been explored using a 1.7 MV Pelletron accelerator. Also, a vibrating Kelvin probe was designed and constructed for the measurement of surface potentials. The electret formation method involved using proton beams of 2 MeV energy to both partially and completely penetrate dielectric samples with metallized back plates to create defect-induced surface potentials. These potentials would likely be more resilient than those of electrets fabricated by current popular methods because the effective charge would be deposited much deeper into the material. The potentials were monitored with a custom built Kelvin probe system. This method was worth exploring as there is currently a need for more resilient electrets in the design of energy efficient micro-electro-mechanical systems (MEMS). Currently, electrets cannot survive certain MEMS fabrication processes. Two types of samples were explored. The first were 150 um thick borosilicate glass slips with a sputter coated gold backing layer. The second were silicon substrates with a 300 nm thick SiO₂ layer deposited on one side and a silver backing layer on the other. The results of this thesis suggest that this charging method is inferior to other methods when applied to 150 um thick borosilicate glass. The borosilicate glass electrets were inferior both with respect to effective surface charge and effective surface charge retention. The effective surface charges attained with the SiO₂/Si samples were also lower than the lowest surface charges commonly achieved by other charging methods. The SiO₂/Si samples irradiated at fluences of 10¹¹ and 10¹³ ions/cm² showed decays comparable to those achieved by other methods as of this writing. This thesis is an overview of the design and construction of a Kelvin probe system, the aforementioned method, and a comparison of the results with the characteristics of electrets fabricated by other methods commonly used today.</p><p>

This thesis will present a search for sterile neutrinos using data taken with the MINOS experiment between 2005 and 2012. MINOS is a two-detector on-axis experiment based at Fermilab. The NuMI neutrino beam encounters the MINOS Near Detector 1km downstream of the neutrino-production target before travelling a further 734km through the Earth's crust, to reach the Far Detector located at the Soudan Underground Laboratory in Northern Minnesota. By searching for oscillations driven by a large mass splitting, MINOS is sensitive to the existence of sterile neutrinos through looking for any energy-dependent perturbations using a charged-current sample, as well as looking at any relative deficit in neutral current events between the Far and Near Detectors. This thesis will discuss the novel analysis that enabled a search for sterile neutrinos covering five orders of magnitude in the mass splitting and setting a limit in previously unexplored regions of the sterile neutrino parameter space, where a 3+1-flavour phenomenological model was used to extract parameter limits. The results presented in this thesis are sensitive to the sterile neutrino parameter space suggested by the LSND and MiniBooNE experiments.

Leptogenesis is a class of scenarios where the baryon asymmetry of the Universe is produced from a lepton asymmetry generated in the decays of a heavy sterile neutrino. We explain the motivation for<br />leptogenesis. We review the basic mechanism, and describe subclasses of models. We then focus on recent developments in the understanding of leptogenesis: finite temperature effects, spectator processes, and in particular the significance of flavour physics.

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