School of Physics - Theses

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    The origin of matter and dark matter
    Lonsdale, Stephen J. ( 2018)
    Why is the mass density of dark matter throughout the universe similar to that of ordinary matter? Asymmetric symmetry breaking models can explain this apparent coincidence by exploring how dark matter could naturally have a similar mass to the proton and how the number density of dark matter particles could be almost the same as ordinary nucleons. In this work models of high energy scale mirror symmetry connecting the standard model to an exact copy are spontaneously broken to produce models of asymmetric dark matter, with composite dark matter candidates, that naturally solve the dark matter mystery.
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    Phenomenology of particle dark matter
    Leane, Rebecca Kate ( 2017)
    The fundamental nature of dark matter (DM) remains unknown. In this thesis, we explore new ways to probe properties of particle DM across different phenomenological settings. In the first part of this thesis, we overview evidence, candidates and searches for DM. In the second part of this thesis, we focus on model building and signals for DM searches at the Large Hadron Collider (LHC). Specifically, in Chapter 2, the use of effective field theories (EFTs) for DM at the LHC is explored. We show that many widely used EFTs are not gauge invariant, and how, in the context of the mono-W signal, their use can lead to unphysical signals at the LHC. To avoid such issues, the next iteration of a minimal DM framework, called simplified models, are considered. We discuss use of such models at the LHC in Chapter 3, and show that in the context of a renormalizable gauge-invariant theory, any isospin violating effects in mono-W signals cannot be large. In Chapter 4, we discuss an alternative search strategy to mono-X searches at the LHC — in the case that DM does not couple directly to hadrons, the mono-X signature does not exist, and instead a leptophilic DM signature can be probed. We focus on the prospects for leptophilic DM with a spin-1 mediator at the LHC, and discuss constraints from other experiments. In the third part of this thesis, we turn to astrophysical signals of DM. In Chapter 5, we show that a consequence of enforcing gauge invariance in simplified DM models provides a new dominant s-wave DM annihilation process for indirect detection searches, and set limits on the annihilation cross section from Pass 8 observations of the Fermi Gamma-ray Space Telescope. In Chapter 6, we demonstrate the impact of mass generation for simplified models, finding that the relic density and indirect detection constraints, along with the DM interaction types, are strongly dictated by the mass generation mechanism chosen. In Chapter 7, we show that the multi-mediator approach advocated in the previous two chapters can also lead to a new dominant signal, in the form of dark initial state radiation. Finally in Chapter 8, we look to the Sun to find that if DM annihilates to long-lived mediators, the gamma rays and neutrinos produced can be strongly probed by gamma-ray telescopes and observatories Fermi-LAT, HAWC, and LHAASO, as well as neutrino telescopes IceCube and KM3Net. Interestingly, these telescopes can provide the strongest probe of the DM spin dependent scattering cross section, outperforming standard high-energy solar neutrino searches and direct detection experiments by several orders of magnitude.
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    Mono-X searches for simplified models of dark matter
    BRENNAN, AMELIA ( 2016)
    The identity of dark matter remains one of the big open questions in particle physics; while much is known about its distribution throughout the Universe, very little is understood about its particle nature. In particular, a small but non-zero coupling to the Standard Model (SM) sector has not yet been ruled out. WIMP-type dark matter (DM), with weak-scale mass and couplings, may therefore be produced in proton collisions with the Large Hadron Collider (LHC), and detected by the ATLAS experiment. Several collider searches are presented, which utilise the mono-X+ MET (missing transverse energy) topology, wherein DM (the presence of which is inferred through the observation of missing transverse energy) is produced in association with some object X. The mono-jet process has the largest cross section, however mono-boson analyses, the focus of this thesis, have other advantages. The mono-Z(l+l−) channel benefits from the straightforward identification of charged leptons within the detector and removal of the multi-jet background, while the mono-W/Z(jj) channel is able to utilise the growing collection of electroweak boson identification techniques which exploit the two-prong substructure of a large-radius jet. This thesis describes two ATLAS analyses that seek to constrain both Effective Field Theory (EFT) models and simplified models of DM. The ATLAS mono-Z(ll) analysis uses 20.3 fb−1 of data produced at 8 TeV and selects events with a leptonically-decaying Z boson produced back-to-back with a large amount of MET. A cut-and-count method finds that no excess above the SM prediction is observed, and so constraints are calculated for the suppression scale Λ of the EFTs, and for the quark-DM-mediator coupling of a simplified model with a scalar mediator exchanged in the t-channel. The ATLAS mono-W/Z(jj) analysis uses the first 3.2 fb−1 of data produced at 13 TeV, and selects events with a single large-radius jet produced in association with MET. A profile likelihood fit of the SM background estimation and data is used to extract a limit on the signal strength for a vector mediator s-channel simplified model, and converted to a limit on the suppression scale Λ for a ZZχχ contact operator. A reinterpretation of Run I results from ATLAS for three common simplified models is also presented, including a comparison of the results from the mono-jet, mono-Z(l+l−) and mono-W/Z(jj) channels. Limits on the model coupling strengths are discussed. The strongest constraints are obtained with the mono-jet channel, however the leptonic mono-Z channel is able to remove the large multi-jet background to attain limits that are weaker by only a factor of a few. It is essential that the reconstruction of objects within the ATLAS detector, along with their energy measurement and calibration, is well understood and that the performance is optimised. Along with a general discussion of the relevant objects in the detector (leptons, jets and MET), the in situ measurement of corrections to the energy scale of hadronically-decaying tau leptons is described.
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    Physics beyond the standard model
    Clarke, Jackson David ( 2016)
    In this Thesis we present a collection of original bodies of work pertaining to a number of theoretical/phenomenological questions of the Standard Model, as studied from a "bottom-up" perspective. In Chapter 2: Higgs Sector, we consider the implications of extending the Standard Model Higgs sector by a very light (100 MeV < $m_s$ < $m_h/2$) real singlet scalar field. We identify the regions of parameter space which experiments at the Large Hadron Collider are uniquely sensitive to. There is a strong focus on low background displaced decay signatures. In Chapter 3: Naturalness, we show how a Higgs mass sensitivity measure can be rigorously derived from Bayesian probability theory. We use this measure to constrain the masses of various fermionic and scalar gauge multiplets, obtaining naturalness bounds of O(1-100) TeV. In Chapter 4: Neutrino Mass, we write down the minimal UV completions for all the Standard Model dimension 7 operators which might be responsible for the radiative generation of Majorana neutrino masses. A detailed collider study of a one-loop realisation is performed. In Chapter 5: Baryon Asymmetry of the Universe, we present a proof that the three-flavour Type I seesaw model cannot provide an explanation for neutrino masses and the baryon asymmetry of the Universe via hierarchical leptogenesis without introducing a Higgs naturalness problem. We then describe a minimal extension (the "$\nu$2HDM") which can avoid this conclusion. In Chapter 6: Strong CP Problem, we describe a very minimal model (the "$\nu$DFSZ") which can explain neutrino masses, the baryon asymmetry of the Universe, the strong CP problem, and dark matter, without introducing a naturalness problem for the Higgs. This model serves as an existence proof that weakly coupled high scale physics can naturally explain phenomenological shortcomings of the Standard Model. Lastly, in Chapter 7: Dark Matter, we consider the implications of a class of self-interacting "plasma dark matter" models for direct detection experiments. A number of qualitatively unique signatures (when compared to single component collisionless dark matter) are identified. We emphasise the prediction for a signal which modulates with sidereal day.
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    Lyα emitters as a probe of galaxy formation and ionisation history
    BRUNS JR, LOREN ( 2016)
    Current observations suggest that the reionisation of hydrogen in the intergalactic medium had begun by z ∼ 10 and was completed around z ∼ 6. Directly observing this epoch is not possible with existing instrumentation, making it difficult to infer how the increased ionising background during this period affected galaxy formation. This thesis aims to put constraints on the galaxy formation history of the Universe with existing instruments, by modelling and observing the number densities of observed Lyα emitters in the ionised environments around z ∼ 2 − 3 quasars to mimic conditions found during the epoch of reionisation. The main work presented is a model for the ionisation state of the intergalactic medium around star forming galaxies in the vicinity of a luminous quasar, tuned by empirical relationships from conditions at z ∼ 2 − 3. This model suggests that the intense ionising radiation from a quasar offsets the increased density of the intergalactic medium found around it, implying that the direct detection of star forming galaxies by their Lyα emission in the vicinity of z ∼ 2 − 3 quasars is less obstructed by the intergalactic medium than galaxies in the field. The accuracy of this model is compared to existing Lyα galaxy surveys and found to be in good agreement. Discrepancies exist between the expected number of Lyα emitting galaxies this model predicts and the surveyed region around the super-luminous quasar PKS 0424-131, in which no Lyα emission was detected. The modelling done suggests that in order to be consistent with this null detection at the 68% (90%) level, galaxies below 2.5×10^12 M⊙ (4.2×10^12 M⊙) must be omitted. These results suggest that considerable radiative suppression of galaxy formation by PKS 0424-131 is taking place. This hypothesis is tested using observations made on the Baade telescope at the Las Campanas Observatory with the Maryland Magellan Tunable Filter. The unique suitability of tunable filters for the detection of high-redshift galactic Lyα emission is described in detail, along with their idiosyncratic calibration and data reduction processes. The adverse seeing conditions make it impossible to put limits on the impact of ionising radiation of galaxy formation using these observations, and an analysis of the factors that prevented detection is provided. Finally, suggestions are made for ways to improve the chance of success for future observations of this effect using tunable filters, as well as ways to remove spurious ghost reflections in the data analysis that are unique to tunable filter observations.
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    Direct shear mapping: the first technique to measure weak gravitational shear directly
    de Burgh-Day, Catherine Odelia ( 2015)
    This thesis develops and tests a new technique, called Direct Shear Mapping (DSM), to measure weak gravitational lensing shear, $\gamma$, directly from observations of a single background source. The technique assumes the velocity map of an un-lensed, stably-rotating galaxy will be rotationally symmetric. Lensing distorts the velocity map, making it asymmetric. The degree of lensing can be inferred by determining the transformation required to restore axisymmetry. This technique is in contrast to traditional weak lensing methods, which require averaging an ensemble of background galaxy ellipticity measurements, to obtain a single shear measurement. The accuracy of the fitting algorithm is tested in simulated data with a suite of systematic tests. It is demonstrated that in principle shears as small as $0.01$ can be measured. The shear is then fitted in very low redshift (and hence un-lensed) velocity maps, and a null result is obtained with an error of $\pm 0.01$. The high sensitivity achievable with DSM results from analysing spatially resolved spectroscopic images, including not just shape information (as in traditional weak lensing measurements) but velocity information as well. To investigate the prospects for making nonzero shear measurements with DSM in current and future surveys, a theoretical estimate is made of the frequency of galaxy-galaxy weak lensing at low redshift. The probability of weak lensing at low redshifts is found to be good (1 in 1,000 galaxies at $z\sim 0.2$). An algorithm is then presented to make an empirically driven estimate of the frequency of occurrence of weak lensing in existing low redshift galaxy survey data. This algorithm is applied to the Galaxy and Mass Assembly Phase 1 Survey Data Release 2 catalogue. It is estimated that to a redshift of $z\sim 0.6$, the probability of a galaxy being weakly lensed by at least $\gamma = 0.02$ is $\sim$0.01. A technique is then demonstrated to measure the scatter in the stellar mass-halo mass relation using a simulated sample of low redshift DSM shear measurements. It is estimated that for a shear measurement error of $\Delta\gamma = 0.02$, this measurement could be made with a sample of $\sim$50,000 spatially and spectrally resolved galaxies. Finally, the first step towards extending DSM to incorporate weak lensing flexion is made. Including flexion in a lensing analysis increases the sensitivity of weak lensing measurements, and facilitates measurement of the gradient of the gravitational potential. Weak lensing convergence, shear, and flexion field variables are derived for a generalised lensing mass, without assuming circular symmetry. It is shown that the equations reduce back to the correct expressions for simple lens mass distributions, and when solved numerically for circularly symmetric lenses reproduce the results obtained for analytical solutions. Finally, the equations are solved numerically for a simple non-circularly symmetric lens.
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    Interacting dark matter: decay and bremsstrahlung processes
    Galea, Ahmad Jacob ( 2013)
    Though there is substantial indirect astrophysical evidence for the existence of dark matter (DM), it has yet to be directly detected. Consequently, little is known about its internal structure. It is possible that there is a small but finite non-gravitational interaction between dark matter and the Standard Model (SM) which may have observable consequences. The purpose of this thesis is the exploration of some of these interactions and consequences. In particular we consider the possibility that dark matter is unstable on long timescales, as motivated by discrepancies between simulation and observation of structure on sub-galactic scales. We also consider the consequences of electroweak radiative corrections to annihilation processes involving dark matter, as such corrections are necessarily present in many well motivated models. We consider this possibility in the contexts of dark matter annihilation in galactic halos, and production in colliders. Chapter 1 provides an introduction to dark matter, including some of its astrophysical and particle aspects. As a motivation for the following sections, we begin by briefly outlining some of the observational evidence for dark matter. We go on to discuss structure formation, and the cold dark matter distribution on galactic scales. Next we discuss the possibility of non-gravitational interactions involving dark matter, including decay, annihilation, scattering off nuclei, and production. Finally we discuss the determination of the relic abundance in the early Universe, including a discussion of models involving coannihilation. Late decaying dark matter has been proposed as a solution to the small scale structure problems inherent to cold dark matter cosmology. In these models the parent dark matter particle is unstable, and decays into a daughter with near degenerate mass, plus a relativistic final state. In Chapter 2 we review the observational constraints on decaying dark matter, and construct explicit particle physics models to realize this scenario. To achieve this, we introduce a pair of fermionic dark matter candidates and a new scalar field, which obey either a Z4, or a U(1) symmetry. Through the spontaneous breaking of these symmetries, and coupling of the new fields to standard model particles, we demonstrate that the desired decay process may be obtained. We also discuss the dark matter production processes in these models. In Chapter 3 we investigate electroweak radiative corrections to dark matter annihilation into leptons, in which a W or Z boson is also radiated. In many dark matter models the annihilation rate into fermions is helicity suppressed. We demonstrate that bremsstrahlung processes can remove this helicity suppression, causing the branching ratios Br($\ell \nu W $), Br($\ell^+\ell^-Z$), and Br($\bar\nu \nu Z$) to dominate over Br($\ell^+\ell^-$) and Br($\bar\nu \nu$). We find this effect to be most significant in the limit where the dark matter mass is nearly degenerate with the mass of the boson which mediates the annihilation process. Finally, in Chapter 4, we investigate a mono-Z process as a potential dark matter search strategy at the Large Hadron Collider (LHC). In this channel a single Z boson recoils against missing transverse momentum attributed to dark matter particles, $\chi$, which escape the detector. For illustrative purposes we consider the process $q\bar{q} -> \chi\chi Z$ in a toy dark matter model, where the Z boson is emitted from either the initial state quarks, or from the internal propagator. We look for muonic decays of the Z, showing the Standard Model backgrounds to this process to be easily removable with modest selection cuts. We compare signal with Standard Model backgrounds and demonstrate that there exist regions of parameter space where the signal may be clearly visible above background in future LHC data.
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    The broad emission line region of quasars and gravitational lensing by early-type galaxies
    Ruff, Andrea Joy ( 2012)
    This thesis has focused on predicting emission line flux ratios from the broad emission line region of quasars under different physical conditions, and measuring the dark matter fraction and total mass density slope within early-type galaxies using gravitational lensing. Quasars are the energetic cores of distant galaxies, and they reside in some of the oldest, most massive objects formed in the universe. Due to their incredible luminosity (as much as $10^5$ times greater than a typical galaxy), quasars can be observed at extremely large distances. Quasars have a unique spectrum, with bright, broad emission lines that are produced by photoionised gas that is close to the central super-massive black hole. Despite the prominence of these broad emission features, the gas physical conditions and the geometry of the emission region are poorly understood. Due to its small scale and large distance, the emission line region cannot be resolved directly — even with the most powerful telescopes — and simulations are required to understand the mechanism that produces the unique quasar spectrum. Using simulations of micro-physical processes, including photoionisation, the broad emission line flux ratios can be calculated for a range of gas densities and distances from the central black hole. Using the photoionisation code, Cloudy, hydrogen and helium line emission was over the range of possible broad emission line region conditions. The hydrogen and helium lines are of particular interest because the line emission has strong dependence on the gas number density and incident ionising flux, whilst having only a negligible dependence on several other free parameters of the model. These simulations were then used to find a set of interesting ratios that can be used to determine the limits on the upper limit on the gas number density, and outer radius of the emission region. This thesis demonstrates a new technique for determining the physical conditions of the broad line emitting gas in quasars, using optical and near-infrared hydrogen and helium emission lines. Near-infrared line ratios are advantageous, as they have a negligible dependence on the amount of internal dust. A locally optimally emitting cloud model of the broad emission line region was applied to four nearby (z $\sim$ 0.2) quasars from the Glikman et al. (2006) sample. By comparing simulated emission line ratios to measured ratios from optical and near-infrared spectroscopy, the physical conditions required to produce the observed emission lines were inferred. The model provides a good fit to three of the objects, and a fair fit to the fourth object. We find that low incident ionising fluxes ($phi <10^{18}$cm^-2 s^-1), and high gas densities (n>10^{12} cm^-3) are required to reproduce the observed line ratios. This analysis demonstrates that the use of composite spectra in photoionisation modelling is inappropriate; models must be fitted to the individual spectra of quasars. This thesis also derives properties of early-type galaxies using a joint gravitational lensing and stellar-dynamics analysis. The sample consists of 11 early-type galaxies from the Strong Lenses in the Legacy Survey (SL2S). The median deflector redshift is 0.5, making it the largest sample of intermediate redshift lenses that have been studied using a joint lensing and dynamics analysis. By combining measured redshifts and stellar velocity dispersions from Keck spectroscopy with lens models from Gavazzi et al. (2012, submitted), the total mass density slope inside the Einstein radius for each of the 11 lenses was derived. The average total density slope was found to be 2.16$\pm$0.9, with an intrinsic scatter of 0.25. The dark matter fraction for each lens within half the effective radius was also determined. The average projected dark matter mass fraction was found to be 0.42$\pm$0.08 with a scatter of 0.25 for a Salpeter initial mass function. By combining the SL2S results with those from previous studies, a mild trend in the cosmic evolution of the total mass density slope was found. This suggests that the total density profile of massive galaxies has become slightly steeper over cosmic time. If this result is confirmed by larger samples, it would indicate that either dissipative processes or off-axis major mergers play an important role in the growth of massive galaxies since a redshift of 1.
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    Dark matter indirect detection and Bremsstrahlung Processes
    Jacques, Thomas David ( 2011)
    It is now well established that some form of Dark Matter (DM) makes a sizeable contribution to the total matter-energy abundance of the Universe, yet DM still evades detection and its particle properties remain unknown. Indirect detection provides an important probe of some of these fundamental properties. DM self-annihilation throughout the Universe is expected to lead to an observable signal of standard model particles at Earth, and any observed flux of standard model particles from a particular region acts as an upper limit on the annihilation signal from that region. In Chapter 1, we give an introduction to our current knowledge of DM. We begin with the historic and recent evidence for the existence of DM based on its gravitational effects, before describing our current knowledge of DM formation history and abundance. We then describe and compare a number of competing DM density profiles for our galaxy, highlighting the large uncertainties towards the Galactic center. There are currently a large number of DM candidates, sometimes called the `Candidate Zoo'. We briefly introduce several of the most popular candidates, describing their history and motivation. We then move on to describe current searches for DM, focusing on indirect detection, which aims to detect DM via an observable flux of its SM annihilation products. We detail the major constraints on the DM self-annihilation cross section, and examine some potential signals from DM annihilation. We also describe constraints on DM from direct detection and collider searches. Finally, we introduce bremsstrahlung processes in the context of DM annihilation, where a particle such as a gamma-ray is radiated from one of the DM annihilation products at the Feynman diagram level. In Chapter 2, we use gamma-ray data from observations of the Milky Way, Andromeda (M31), and the cosmic background to calculate robust upper limits on the dark matter self-annihilation cross section to monoenergetic gamma rays, $\langle v\sigma \rangle_{\gamma \gamma}$, over a wide range of dark matter masses. We do this in a model-independent and conservative way, such that our results are valid across a broad spectrum of DM models and astrophysical assumptions. In fact, over most of this range, our results are unchanged if one considers just the branching ratio to gamma rays with energies within a factor of a few of the endpoint at the dark matter mass. If the final-state branching ratio to gamma rays, $Br(\gamma \gamma)$, were known, then $\langle v\sigma \rangle_{\gamma \gamma} / Br(\gamma \gamma)$ would define an upper limit on the {\it total} cross section. %we conservatively assume $Br(\gamma \gamma) \gtrsim 10^{-4}$. In Chapter 3, we take advantage of the fact that annihilation to charged leptons will inevitably be accompanied by gamma rays due to radiative corrections to place similar limits on the the annihilation cross section to an electron-positron pair, $\langle v\sigma \rangle_{e^+e^-}$. Photon bremsstrahlung from the final state particles occurs at the Feynman diagram level, yet the gamma-ray spectrum per annihilation is approximately model independent, such that our analysis applies to a broad class of DM models. We compare the expected annihilation signal with the observed gamma-ray flux from the Galactic Center, and place conservative upper limits on the annihilation rate to an electron-positron pair. We also constrain annihilation to muon and tau lepton pairs. We again make conservative choices in the uncertain dark matter density profiles, and note that our constraints would only be strengthened if the density were more tightly constrained. The spectrum per annihilation produces hard gamma rays near the kinematic cutoff, and we find that the constraints on $\langle v\sigma \rangle_{e^+e^-}$ are weaker than those on $\langle v\sigma \rangle_{\gamma \gamma}$ only by a factor of $\sim 10^{-2}$, as expected since the $2\rightarrow 3$ process is suppressed relative to the $2\rightarrow 2$ process. Annihilation to leptons will also be accompanied by massive gauge bosons due to electroweak radiative corrections. In Chapter 4 we examine a case where DM annihilates exclusively to neutrinos at the $2\rightarrow 2$ level, and gamma rays, leptons and hadrons will inevitably be produced due to electroweak bremsstrahlung. We explicitly calculate the ratio of the rate for the three electroweak bremsstrahlung modes $\chi\chi\rightarrow \nu\bar\nu Z,\, e^+ \nu W^-\, e^- \bar \nu W^+$ to the rate for the $2\rightarrow 2$ process $\chi\chi\rightarrow \nu\bar\nu$. Electroweak bremsstrahlung plays a larger role in the special case where the annihilation rate to leptonic modes suffers helicity suppression. While it has long been known that photon bremsstrahlung can lift the helicity suppression, we show in Chapter 5 that electroweak bremsstrahlung is also capable of lifting this suppression, such that the branching ratio to the 3-body electroweak bremsstrahlung final states can greatly exceed the branching ratio to an electron-positron or neutrino pair. We explicitly calculate the electroweak bremsstrahlung cross section in a typical leptophilic model. In Chapter 6 we examine observational signatures of dark matter annihilation in the Milky Way arising from these electroweak bremsstrahlung contributions to the annihilation cross section. Here we calculate the spectra of stable annihilation products produced via $\gamma/W$/$Z$-bremsstrahlung. After modifying the fluxes to account for the propagation through the Galaxy, we set upper bounds on the annihilation cross section via a comparison with observational data. We show that stringent cosmic ray antiproton limits preclude a sizable dark matter contribution to observed cosmic ray positron fluxes in the class of models for which the bremsstrahlung processes dominate.
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    Quasar microimaging
    Bate, Nicholas Frazer ( 2010)
    Observations of gravitationally microlensed quasars offer a unique opportunity to probe quasar structure on extremely small scales. In this thesis, we conduct extensive microlensing simulations and compare with observational data to constrain quasar accretion discs, and conduct preliminary probes of broad emission line region structure. This analysis is done using a new single-epoch imaging technique that requires very little telescope time, and yet produces results that are comparable to those obtained from long-term monitoring campaigns. We begin by exploring the impact of variable smooth matter percentage and source size on microlensing simulations. Adding a smooth matter component affects minimum and saddle point images differently, broadening the magnification distribution for the saddle point image significantly. However, increasing the radius of the background source washes out this difference. The observation of suppressed saddle point images can therefore only be explained by microlensing with a smooth matter component if the background source is sufficiently small. We use these simulations, in combination with I-band imaging of the lensed quasar MG 0414+0534 to constrain the radius of the quasar source. This demonstrates the viability of a single-epoch imaging method for constraining quasar structure. This technique is then expanded to single-epoch multi-band observations, in order to constrain the radial profile of quasar accretion discs as a function of observed wavelength. We present new Magellan observations of two gravitationally lensed quasars: MG 0414+0534 and SDSS J0924+0219. We also analyse two epochs of Q2237+0305 data obtained from the literature. Our results are compared with four fidicial accretion disc models. At the 95 per cent level, only SDSS J0924+0219 is inconsistent with any of the accretion disc models. When we combine the results from all three quasars -- a first step towards assembling a statistical sample -- we find that the two steepest accretion disc models are ruled out with 68 per cent confidence. In addition, we are also able to use our microlensing simulations to constrain the smooth matter percentages in the lenses at the image positions. In both MG 0414+0534 and SDSS J0924+0219 we find smooth matter percentages that are inconsistent with zero. A smooth matter percentage of approximately 50 per cent is preferred in MG 0414+0534, and approximately 80 per cent in SDSS J0924+0219. Q2237+0305 is usually assumed to have a smooth matter percentage of zero at the image positions, as they lie in the bulge of the lensing galaxy. Though our measurement is consistent with a zero smooth matter percentage, there is a peak in the probability distribution at a value 20 per cent. This is perhaps a hint of additional intervening structures along the line of sight to the background quasar. We test the sensitivity of our accretion disc constraints to a range of modelling parameters. These include errors in lens modelling, Bayesian prior probability selection, errors in observational data, and the microlens mass function. Constraints on the power-law index relating source radius to observed wavelength are found to be relatively unaffected by changes in the modelling parameters. Constraints on source radii are found to be more strongly affected. Finally, the broad emission line region of Q2237+0305 is examined. Gemini IFU observations are presented clearly showing differential microlensing across the velocity profile of the CIII] emission line. To analyse this signature, we present three simple broad emission line region models: a biconical outflow, a Keplerian disc, and spherical infall. A method is developed to compare the shapes of simulated flux ratio spectra with the observed spectrum. We are unable to discriminate between the biconical outflow and Keplerian disc models when we average over all viewing angles and orientations. The spherical infall model, however, does not fit the observed data. We also find that for the non-spherically symmetric geometries, low inclination angles are essentially incompatible with the observations. This analysis offers hope that with sufficiently high signal-to-noise observations, differential microlensing signatures may allow us to constrain the geometry and kinematics of this poorly understood portion of quasar structure.