This thesis documents studies of CP violation in B^± to [K_S⁰h⁺h⁻]_DK^±, (h = π/K) decays using data taken by the LHCb experiment during 2011, and the first measurement of γ to be made at the Large Hadron Collider (LHC), γ = (45+43-38) degrees. Also included is a study of D⁰ to K_S⁰K^∓π^± decays using CLEO III and CLEO-c data, resulting in the first amplitude models to be published for these decays and a measurement of the ratio of their branching fractions.

This thesis describes the design a novel type of particle accelerator for charged particle therapy. The accelerator is called a non-scaling, Fixed Field Alternating Gradient (ns-FFAG) accelerator, and will accelerate both protons and carbon ions to energies required for clinical use. The work is undertaken as part of the PAMELA project. An existing design for a ns-FFAG is taken as a starting point and analysed in terms of its ability to suit the charged particle therapy application. It is found that this design is particularly sensitive to alignment errors and would be unable to accelerate protons and carbon ions at the proposed acceleration rate due to betatron resonance crossing phenomena. To overcome this issue, a new type of non-linear ns-FFAG is developed which avoids resonance crossing and meets the requirements provided by clinical considerations. Two accelerating rings are required, one for protons up to 250 MeV and fully stripped carbon ions to 68 MeV/u, the other to accelerate the carbon ions up to 400-430 MeV/u. Detailed studies are undertaken to show that this new type of accelerator is suitable for the application. An alignment accuracy of 50 micrometers will not have a detrimental effect on the beam and the dynamic aperture for most lattice configurations is found to be greater than 50 pi.mm.mrad normalised in both the horizontal and vertical plane. Verification of the simulation code used in the PAMELA lattice design is carried out using experimental results from EMMA, the world's first ns-FFAG for 10-20 MeV electrons built at Daresbury Laboratory, UK. Finally, it is shown that the described lattice can translate into realistic designs for the individual components of the accelerator. The integration of these components into the PAMELA facility is discussed.

Two analyses are performed using data collected by the LHCb experiment during 2011. Both consider decays of charged B mesons reconstructed in the π±μ+μ− final state. Decays involving dimuons provide an experimentally clean signature, even in the high-background environment of the √s = 7 TeV proton-proton collisions at the LHC. The first analysis measures the CP asymmetry of B±→Ψπ± decays using 0.37 fb-1 of data, where the dimuon decays of two resonances are considered, J/ψ→μ+μ− and ψ(2S)→μ+μ−. The branching fraction is measured relative to the Cabibbo favoured B±→ΨK± mode. The second analysis uses 1 fb-1 of data to make the first observation of the non-resonant B±→π±μ+μ− decay. The branching fraction is measured relative to that of B±→K±μ+μ−, and measurements of the CP asymmetry and the ratio of CKM matrix elements Vtd/Vts are obtained. The branching fractions of the decays of interest are found to be B(B±→J/ψ π±) = (3.88 ± 0.11 ± 0.15) x 10-5, B(B±→ψ(2S) π±) = (2.52 ± 0.26 ± 0.15) x 10-5 and B(B±→π±μ+μ−) = (2.48 + 0.57 −0.52 ± 0.17) x 10-8, where the first uncertainty is related to the statistical size of the sample and the second quantifies systematic effects. The measured CP asymmetries in these modes are A CP (J/ψ π) = 0.005 ± 0.027 ± 0.011, A CP (ψ(2S) π) = 0.048 ± 0.090 ± 0.011 and A CP (μμπ) = -0.045 ± 0.220 ± 0.066, with no evidence of direct CP violation seen. The ratio of matrix elements is measured as Vtd/Vts = 0.274 + 0.031 − 0.028 ± 0.008, which is in agreement with previous results.

In this work we analyze various implications of the presence of large field vacum expectation values (VEVs) along supersymmetric flat directions during the early universe. First, we discuss supersymmetric leptogenesis and the gravitino bound. Supersym- metric thermal leptogenesis with a hierarchical right-handed neutrino mass spectrum normally requires the mass of the lightest right-handed neutrino to be heavier than about 109 GeV. This is in conflict with the upper bound on the reheating temperature which is found by imposing that the gravitinos generated during the reheating stage after inflation do not jeopardize successful nucleosynthesis. We show that a solution to this tension is actually already incorporated in the framework, because of the presence of flat directions in the supersymmetric scalar potential. Massive right- handed neutrinos are efficiently produced non-thermally and the observed baryon asymmetry can be explained even for a reheating temperature respecting the gravitino bound if two conditions are satisfied: the initial value of the flat direction must be close to Planckian values and the phase-dependent terms in the flat direction potential are either vanishing or sufficiently small. We then show that flat directions also contribute to the total curvature perturbation. Such perturbation is generated at the first oscillation of the flat direction condensate when the latter relaxes to the minimum of its potential after the end of inflation. If the contribution to the total curvature perturbation from supersymmetric flat direction is the dominant one, then a significant level of non-Gaussianity in the cosmological perturbation is also naturally expected. Finally, we argue that supersymmetric flat direction VEVs can decay non perturbatively via preheating even in the case where they undergo elliptic motion in the complex plane instead of radial motion through the origin. It has been generally argued that in this case adiabaticity is never violated and preheating is inefficient. Considering a toy U(1) gauge theory, we explicitly calculate the scalar potential, in the unitary gauge, for excitations around several flat directions. We show that the mass matrix for the excitations has non-diagonal entries which vary with the phase of the flat direction vacuum expectation value. Furthermore, this mass matrix has zero eigenvalues whose eigenstates change with time. We show that these light degrees of freedom are produced copiously in the non-perturbative decay of the flat direction VEV.

This thesis will describe the latest work from the Feedback On Nanosecond Timescales project, commonly known as FONT. The goal of the FONT project is the development of a beamline feedback system to be installed at the interaction point (IP) of a future linear collider in order to maximize the luminosity that can be achieved. The prototype FONT feedback system is beam-based, meaning that the correction is determined from direct measurement of the position of the beam, and intra-train, meaning that the correction is applied within the duration of the current bunch train. The FONT system, consisting of three stripline beam position monitors, a digital processor unit built around a Field Programmable Gate Array (FPGA) and a pair of electromagnetic kickers, is described. Recent improvements to the position measurement process are detailed and the performance of the feedback system is presented. The modification of the firmware to operate on a machine with a large number of bunch trains, such as the International Linear Collider, is described and the design is verified through the use of a laboratory test bench developed to simulate such a machine. The FONT5 digital board is proved capable of operating on a train resembling the specification for the International Linear Collider: 2820 bunches separated in time by 308 ns.

This thesis reports an analysis of 3.0fb^-1 of pp collision data collected by the LHCb experiment in 2011 and 2012. Decays of neutral B mesons to neutral D mesons and excited neutral kaons are reconstructed, because of their sensitivity to the CP-violating phase of the CKM matrix, γ.

This thesis studies the cosmology of ultra-light scalar fields with masses in the range 10⁻³³ eV ? m ? 10⁻¹⁸ eV and their effects on cosmology. The existence of such fields is motivated by the theoretical framework of the "String Axiverse". All types of string theory contain multiple axion fields associated with antisymmetric tensor fields compactified on closed cycles in the compact space. Since the masses of these fields scale exponentially with the volume of the cycle, it is possible for them to be naturally light. We study the effects of these fields as a component of the dark matter and show analytically and numerically that they cause a suppression of structure formation on cosmological scales set by the inverse mass. We show that it will be possible with future galaxy redshift and weak lensing surveys to detect an ultra- light field comprising of order a percent of the total dark matter. If such a field is allowed to couple to the geometry that provided its mass via a phenomenological scalar potential for the axion and modulus, then the expansion of the universe can be altered significantly. In particular, we find that it is possible to have multiple epochs of accelerated expansion over a large region of parameter space, and to have a flat universe with a big crunch in the distant future. Finally, we address the issue of isocurvature perturbations in axion cosmologies, and demonstrate that in the ultra-light case the power spectrum is effected. This may have implications for the conclusions made about fine tuning in the axiverse in relation to a potential detection of tensor modes in the CMB that are different to the case of a standard axion.

This thesis documents two studies of the neutral charm meson system using the LHCb detector, and gives an overview of the numerous changes made to the LHCb software trigger in advance of Run 2 of the LHC. In the first analysis, amplitude models are applied to studies of the resonance structure in D⁰ → K⁰_SK^−π⁺ and D⁰ → K⁰_SK⁺π^− decays using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb^−1, collected during Run 1 of the LHC. Relative magnitude and phase information is determined, and coherence factors and related observables are computed for both the whole phase space and a restricted region of 100 MeV/c² around the K*(892)^± resonance. Two formulations for the Kπ S-wave are used, both of which give a good description of the data. The ratio of branching fractions B (D⁰→ K⁰_SK⁺π^−) /B (D⁰→ K⁰_SK^−π⁺) is measured to be 0.655 ± 0.004 (stat) ± 0.006 (syst) over the full phase space and 0.370 ± 0.003 (stat) ± 0.012 (syst) in the restricted region. A search for CP violation is performed using the amplitude models and no significant effect is found. Predictions from SU(3) flavour symmetry for K*(892)K amplitudes of different charges are compared with the amplitude model results, and marginal agreement is found. The second study estimates the sensitivity to D⁰–D⁰ mixing and indirect CP violation parameters that can be achieved using a model-independent technique and the samples of D⁰→ K⁰_SK⁺K^− decays recorded by LHCb in Run 1 and Run 2 of the LHC. These studies show that constraints on these parameters could be significantly improved by an analysis of the anticipated Run 2 dataset.

This thesis presents two measurements made using data collected by the LHCb detector, operating at the Large Hadron Collider accelerator at the CERN particle physics laboratory. The first is a measurement of the production rates of promptly produced D0, D+, Ds+, and D*+ open charm mesons, using data collected in 2015 at a proton-proton centre-of-mass energy of √s = 13 TeV. The second is a search for direct CP violation in two three-body decays of the Lambda_c charm baryon, pKK and ppipi, using data collected in 2011 at √s = 7 TeV and in 2012 at √s = 8 TeV. For each measurement, motivation and context are given from the standpoint of improving the theoretical understanding of the Standard Model and searching for signs of physics that cannot be explained by it, and then the various statistical analysis techniques used to extract physical quantities from the data are explained. The systematic limitations of the method are explored and quantified, and then the results are presented.

This Thesis studies some aspects of string compactifications with particular em- phasis on moduli stabilisation and cosmology. In Chapter 1 I motivate the study of string compactifications as a way to build on the successes of the Standard Model of Particle Physics and of the theory of General Relativity. Chapter 2 constitutes an overview of the technical background necessary for the study of flux compactifications. I sketch how the desire to obtain a supersymmet- ric theory in four dimensions constrains us to consider compactifications of the ten dimensional theory in six dimensional Calabi-Yau orientifolds. I argue that it is strictly necessary to stabilise the geometry of this compact space in order to have a phenomenologically viable four dimensional theory. I introduce the large volume scenario of type IIB compactifications that successfully incorporates fluxes and sub- leading corrections to yield a four dimensional theory with broken supersymmetry and all geometrical moduli stabilised. The next four Chapters are devoted to the study of some phenomenological aspects of moduli stabilisation and constitute the original work developed for this Thesis. In Chapter 3 I investigate the consequences of field redefinitions in the stabilisation of moduli and supersymmetry breaking, finding that redefinitions of the small blow- up moduli do not significantly alter the standard picture of moduli stabilisation in the large volume scenario and that the soft supersymmetry breaking terms are generated at the scale of the gravitino mass. Chapter 4 deals with the putative destabilisation of the volume modulus by very dense objects. The analysis of the moduli potential shows that even the densest astrophysical objects cannot destabilise the moduli, and that destabilisation is only achievable in the context of black hole formation and cosmological singularities. In Chapter 5 I present a model of inflation within the large volume scenario. The inflaton is identified with a geometric modulus, the fibre modulus, and its potential generated by poly-instanton effects. The model is shown to be robust and consistent with current observational constraints. In Chapter 6 I introduce a model of quintessence, where the quintessence field and its potential share the same origin with the inflationary model of the previous Chapter. This model constitutes a stringy realisation of supersymmetric large extra dimensions, where supersymmetry, the low gravity scale and the scale of dark energy are intrinsically connected. I conclude in Chapter 7 outlining the direction of future research.