We Rydberg dress a magneto-optical trap of strontium atoms, mixing Rydberg character into atoms as they are cooled and confined. A recently developed tunable high-power narrow-linewidth 319 nm laser is used to excite and characterise triplet Rydberg states in strontium. Off-resonantly dressing a cloud of atoms in a narrow-line MOT operating on the 5s2 1S0 - 5s5p 3P1 transition, we observe a one-body AC Stark shift on the cloud, which we characterise to identify a regime in which only Rydberg dressed atoms are trapped in the MOT. In this cloud the Rydberg dressed atoms are both trapped and cooled. Increasing atomic density in the dressed MOT, plasma formation is observed at densities lower than the density necessary for observation of Rydberg dressed atoms. This plasma is caused by a build-up of charges due to spontaneous ionisation of Rydberg atoms, which then DC Stark shift the Rydberg state onto resonance with the coupling laser. The high charge density of the plasma then results in strong Rydberg excitation that causes rapid depletion of atoms. Regimes using optimum Rydberg states and charge-extracting electric fields are identified that may prevent plasma formation, and allow the interacting regime to be reached. Such a regime, with cooling, confinement, and tunable interactions, may form the basis of a quantum simulator for dissipative many-body systems.

The world needs solar electricity to replace a large fraction of traditional, fossil-fuel-generated electricity over the coming decades if it is to avoid the worst effects of climate change and continue to meet the needs of an increasingly energy-dependent society. This transition is currently well underway. The installed generating capacity of solar electricity continues to grow exponentially, having reached 307 GW in 2016 (2 % of average global electricity demand), which means that replacing a large majority of fossil fuel use, requiring several terawatts of capacity, in the coming decades is entirely realistic. Cu2ZnSnS4 (CZTS) is a potential material for the absorber layer in photovoltaic solar cells. It has the advantages over silicon, which currently provides 95 % of the solar electricity market, of lower processing costs and a direct band gap, which means much less material is required. Most other alternative absorber materials will ultimately be limited by high material costs, low elemental abundances, or toxicity, but CZTS has none of these problems, making it a very promising material indeed. However, its record photovoltaic efficiency (11.0 %) is well below those of some other materials (>20 %) because of low open-circuit voltage. The outstanding areas of current CZTS research are the absorber-buffer interface, band gap fluctuations caused by point defects, and secondary phases. This thesis presents work investigating the latter two, primarily using bulk samples fabricated by solid-state reaction. Firstly, compositional, structural, and optoelectronic analysis techniques were used to study the effect of composition on material properties. It was found that the quasi-ternary phase diagram commonly used for CZTS is incorrect; and that no common analysis technique can quantify cation disorder in CZTS, despite Raman spectroscopy commonly being used to do so. Secondly, neutron diffraction was used to study the order-disorder phase transition at around 550 K. It was found that the transition temperature is dependent on elemental composition; and that Cu-Zn disorder is present on all cation lattice sites, not merely the 2c and 2d sites of the kesterite crystal structure as has previously been assumed. Thirdly, anomalous X-ray diffraction was used to study cation disorder further. It was found that two distinct phases of CZTS can be present in the same sample, with different elemental compositions resulting from the prevalence of different point defect complexes; two new such types of CZTS were identified; and a mechanism of phase formation was proposed. Finally, a fabrication route for thin-film CZTS by sputtering and sulphurisation annealing was established.

Characterisation of atmospheric seeing and optical turbulence is crucial for the design and operation of modern ground-based optical telescopes. With a new generation of extremely large telescopes being proposed and constructed, new obstacles will be faced with regards to imaging through our turbulent atmosphere. The Differential Image Motion Monitor (DIMM) has been a commonly employed seeing monitor at astronomical observing sites across the world. For decades it has inexpensively provided sites with measurements of the Fried parameter (r0). In this thesis a variation on the current DIMM design will be presented. The Shack-Hartmann Image Motion Monitor (SHIMM) employs a low order Shack-Hartman (SH) lenslet array instead of the two hole aperture mask utilised by the DIMM. The SHIMM is a low-cost, portable instrument, comprised of off-the-shelf components, making it easily duplicated and therefore ideal for comparisons of atmospheric conditions at large observing sites. In this thesis the four key advantages of the SHIMM will be addressed. By utilising a SH lenslet array the SHIMM can employ methods for estimating the value of r0, independent of noise; estimate the atmospheric coherence time; correct for the effect of scintillation on the measurement of r0; and produce a low-resolution fixed three layer turbulence profile. On-sky results of each feature will be presented in this thesis.

In this thesis we study quark flavour physics and in particular observables relating to B meson mixing and lifetimes. Meson mixing arises due to the nature of the weak interaction, and leads to several related observables that are highly suppressed in the Standard Model (SM). Alongside meson mixing, lifetimes provide an insight into rare B processes which can shed light on possible new physics. Both calculations are based on an Effective Field Theory (EFT) framework, in particular the Weak Effective Theory. This framework allows us to separate the high scale effects which are calculable in perturbation theory from the low energy matrix element which are determined through other means. Within this framework, the observables are expanded using the Heavy Quark Expansion (HQE) technique, which utilises the relatively large masses of b and c quarks to reveal a further hierarchy of corrections. The basics of EFTs and the HQE are explored in detail as an entry point to the majority of the work in this thesis. In the rest of the thesis, we take aim at pushing the accuracy of our SM predictions further: by testing the underlying assumption of Quark-Hadron duality in the HQE; by studying possible new physics models that can explain the long standing problem of dark matter as well as recently seen anomalies; and by using alternative approaches to determining the low energy constants associated with mixing and lifetimes in order to provide independent and state-of-the-art results.

In this thesis an experimental model for the interface between the cell membrane and the supporting cytoskeleton has been developed and analysed. The experimental platform is a novel approach to the design of supported membrane based devices and technologies. The system consists of a single component lipid bilayer coupled to an elastic substrate, the area of which can be reversibly increased and decreased. We uncover three independent mechanisms that the membrane may use to respond to changes in substrate area. If the elastic support is partially hydrophilic, the area of the planar portion of the membrane is strongly coupled to the substrate area. The membrane responds to increasing substrate area by absorbing lipid protrusions, and when the substrate area is decreased the excess membrane area is projected back out in the form of lipid tubes. This mechanical remodelling of the membrane occurs above the plane of the support and mimics the passive means of membrane area regulation recently uncovered in live cells. In contrast, when the surface support is completely hydrophilic, two further mechanisms of substrate stress relaxation are uncovered. When the pH of the solu- tion is greater than 7 the membrane is able to slide over the expanding and contract- ing substrate. This membrane sliding motion occurs in the plane of the support and is dynamic. The effectiveness at which membrane tension is relaxed is dependent on the rate at which the substrate area is changed. When the pH is reduced below pH 7, the membrane area becomes strongly coupled to that of the support and the membrane dramatically ruptures, opening large circular pores, in response to substrate deformation. The pores exhibit a dynamic area change, revealing a complex flow of membrane across the support to equilibrate stress. This novel supported membrane behaviour reveals the rich physics possessed by supported lipid systems, that may assist in the design of new supported lipid based technologies.

In this thesis the second-order QCD corrections to electroweak production of a Higgs boson in association with two jets through vector boson fusion are considered. This calculation is fully differential in the kinematics of the Higgs boson and of the final state jets. Infrared divergences are regulated using the antenna subtraction method. We detail the implementation of the process in the parton-level Monte Carlo integrator NNLOJET and present inclusive calculations as well as differential distributions for a wide range of observables at different center-of-mass energies.

The standard ΛCDM model of cosmology has been very successful in matching a large set of observational constraints and describes accurately the evolution of our Universe. Within this framework, the gravitational collapse of cold dark matter structures depends solely on the cosmological background. The formation of galaxies inside these haloes is thought to be determined by complex baryonic process and we rely on numerical techniques to model their effects. Here, we investigate the impact of the cosmological background on galaxy formation. We take the advantage of state of the art cosmological hydrodynamical simulations from the eagle suite to vary the cosmological parameters, in particular, the cosmological constant, to test its effect on the efficiency of star formation. We use this set of new simulations to calculate the likelihood of the observed value of the cosmological constant, given a measure of the multiverse. We discuss the implication of our results in the context of the anthropic principle. We use this framework to develop a fully analytic model of galaxy formation that connects the growth of dark matter haloes in a cosmological background, with the build-up of stellar mass within these haloes. The model identifies the physical processes that drive the Galaxy-Halo co-evolution through cosmic time. Despite the complexity of the baryonic processes involved, galaxy formation is revealed as a remarkably simple process, where the instantaneous star formation efficiency within halos is only a function of their virial temperature and can be described with a ‘single’ differential equation. We find that the model reproduces self-consistently the shape and evolution of the cosmic star formation rate density, the specific star formation rate of galaxies, and the galaxy stellar mass function, both at the present time and at high redshift. Finally, we use the merger rate of supermassive black holes in the eagle simulations to estimate the expected event rate of gravitational wave signals that could be resolved by future space-based gravitational wave detectors. We discuss the power of these detections to provide information about the origin of supermassive black holes and the initial mass distribution of black hole seeds.

Studies of the Drell-Yan process, pp → V + X with V a vector boson, have become an important tool to elucidate the fundamental structure of the Standard Model at particle colliders. The precise theoretical understanding of this process is thus paramount to the further success of programs at modern particle colliders. In this thesis, we present the implementation of a method to improve the electroweak accuracy in the description of these processes within the SHERPA framework. This is achieved by including the next-to-leading order electroweak corrections for the leptonic decays of the massive electroweak bosons, Z, W and Higgs, and the next-to-next-to-leading order QED corrections in the case of Z- and Higgs bosons within the framework of the Yennie, Frautschi and Suura resummation formalism. We find small but potentially observable effects on distributions. Besides the improvement in the theoretical description, phenomenological studies can improve the understanding of the physics at particle colliders. In the second Part of this Thesis we consider b-tagged jets. We study a number of jet shape observables that show good discrimination between a “legitimate”, single b-jet and one originating from a gluon splitting, and further show that the combination of these observables already provides good efficiency in rejecting b-jets from gluon splittings.

In this thesis we investigate what drives the evolution of actively accreting central supermassive black holes and unusually active strongly star-forming galaxies using the Evolution and Assembly of GaLaxies and their Environments (EAGLE) suite of cosmological hydrodynamical simulations. We find that many of our results are intimately tied to the complex evolutionary pathway taken by the central black holes within the simulation. This evolution can be separated into three distinct phases, each related to the mass of the host dark matter halo. In low mass haloes, stellar feedback dominates by driving an effective outflow and substantially hinders the growth of the central black hole. As haloes become more massive, the stellar feedback loses its efficiency, and the outflow stalls. This gives the first opportunity for the central black hole to grow, which is does so initially at a rapid rate. After this phase of rapid growth, the central black hole then becomes sufficiently massive to regulate the gas inflow onto the halo, resulting in both the star formation of the galaxy and any continued rapid growth of the central black hole to be substantially restricted via the outputted energy of an actively accreting supermassive black hole (referred to as an active galactic nuclei, or AGN). In Chapter 2 we discover that this complex evolutionary behaviour is integral to understanding how the growth rates of galaxies and their black holes are related to each other throughout cosmic time. We use this behaviour to explain why the current observational studies report different relationships between galaxy and black hole growth rates depending on the initial selection method used. Finally, in Chapter 3 we find that the evolutionary state of the black hole is also closely connected with high star formation rates in lower mass galaxies ($M_* \lesssim 10^{11}$~\Msol, where $M_*$ is the stellar mass of the galaxy). Such 'starbursting' galaxies are rare, and we argue that they are produced through a culmination of two coinciding events; (1) the galaxy must host an underdeveloped black hole (one that has not yet entered its rapid growth phase), thus ensuring that the galaxy has maintained a gas rich reservoir and contains a low mass black hole; and (2) the galaxy must undergo an interaction to kick-start the starburst process. This tells us that strongly star-forming galaxies are a predominately merger driven population that host undermassive black holes, making them fundamentally distinct from the 'typical' star-forming population.

Throughout this thesis we have sought to construct cost effective, miniature and portable imaging systems to assess a selection of physical parameters re- lated to the the integrity of human skin and epithelial tissue, in vivo. While these technologies can be used for any skin site we, specifically, aim to develop novel non-invasive instrumentation for the diagnosis of menopausal atrophy at point of care. Post-menopause, the outer epithelial layer, begins to thin (at- rophy) and anatomic changes are observed in the vaginal wall cell structure, hydration level, blood oxygenation, epidermal thinning and elasticity (Chapter 2). Yet, despite the profound impact on well-being, there is a significant lack of quantitative tools to measure the epidermal barrier function, or level of atrophisation, in outer skin surfaces and vaginal mucosa. Recent advances in optical microscopy, together with progress in miniature optical components, permit visualisation of living skin tissues. To this purpose we seek to employ existing methodologies such as oximetry, microscopy and imaging modalities within a low cost multifunctional instrument. Particularly we describe the potential use of laser speckle light scattering for surface roughness measure- ment with its limitations and, using numerical models, discuss the parameters that dictate speckle pattern formation. We extend this discussion to rough skin surface with additional bulk scattering from underlying volume tissue (Chapter 3). Through this series of studies we apply our work in laboratory experiments. A range of bench-top instruments were built to measure skin spectral characteristics and additionally a novel single point laser speckle sys- tem towards the measurement of in vivo skin roughness across a selection of volunteers (Chapter 4). In collaboration with industrial partners (Procter and Gamble (P&G) and Lein Applied Diagnostics) we developed a mock up pro- totype towards a novel, non-invasive optical device to quantify patient skin integrity (Chapter 6). This is achieved through a multidisciplinary approach, with novel developments in miniature optical manufacturing and assembly pro- cess (Chapter 5). For future work we outline our protocols, material cost and ways to facilitate these miniature diagnostic instruments for various research and clinical settings.