This dissertation is focused on three lines of work. In the first part, we consider aspects of holography and gauge/gravity duality in lower and higher dimensions. In particular, we study the duality for exact solutions localized on the Randal-Sundrum 2-branes. We also test if some holographic principles in general relativity can be generalized to include higher derivative theories of gravity; namely Lovelock gravity. In the second part we consider the role of pseudo Nambu-Goldstone bosons (pNGBs) in inflationary cosmology. Specifically, we construct an inflationary model using string theory axions, and use these pNGBs to produce the observed coherent magnetic field in the Universe. The third part of the thesis is devoted to the study of the phenomenology of emergent phenomena. We investigated whether one could test if diffeomorphism invariance, the sacred symmetry of general relativity, is emergent. We also construct a new minimal vectorial Standard Model, and argue that the absence of mirror particles predicted by this model can give us a hint about the fundamental nature of space.

Experiment E143 at SLAC performed deep-inelastic scattering measurements with polarized electrons incident on polarized protons and deuterons. The data for the beam energy of 29 GeV cover the kinematical range of $x\sb{\rm Bj}>0.03$ and $1

We demonstrate how the heavy baryon method, previously applied to chiral perturbation theory calculations involving the interactions of nucleons and pions, can be generalized to include interactions with the first nucleon resonance--$\Delta$(1232). The formalism is developed in terms of a small scale $\delta$ expansion, which refers to soft momenta, the pion mass and the nucleon-delta mass splitting $\Delta$ = $M\sb{\Delta} - M\sb{N}$. First applications of this chiral theory are presented, in particular the calculation of mass and wavefunction renormalization, threshold neutral pion photoproduction, and forward Compton scattering.

In this thesis we present two different research projects in theoretical high energy physics. The first part deals with inflationary dynamics of the early universe and its observable consequences in measurements of the cosmic microwave background radiation. Here we investigate how inhomogeneous initial conditions for single field inflation with an initial fast-roll stage can alter the standard inflationary predictions for the power spectrum of the cosmic microwave background at largest scales. In the second part of the thesis we calculate long distance spin effects in gravitational scattering processes. Both classical and quantum corrections arise at the one loop level and are shown to have universal structures with forms and coefficients independent of the spins of the scattered particles. We also include calculations of electromagnetic and of mixed electromagnetic-gravitational scattering.

This thesis reports on two experiments conducted by the HAPPEx (Hall A Proton Parity Experiment) collaboration at the Thomas Jefferson National Accelerator Facility. For both, the weak neutral current interaction (WNC, mediated by the Z0 boson) is used to probe novel properties of hadronic targets. The WNC interaction amplitude is extracted by measuring the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons off unpolarized target hadrons. HAPPEx-III, conducted in the Fall of 2009, used a liquid hydrogen target at a momentum transfer of Q2 = 0.62 GeV2. The measured asymmetry was used to set new constraints on the contribution of strange quark form factors ([special characters omitted]) to the nucleon electromagnetic form factors. A value of APV = −23.803 ± 0.778 (stat) ± 0.359 (syst) ppm resulted in [special characters omitted] = 0.003 ± 0.010 (stat) ± 0.004 (syst) ± 0.009 (FF). PREx, conducted in the Spring of 2010, used a polarized electron beam on a 208Pb target at a momentum transfer of Q 2 = 0.009 GeV2. This parity-violating asymmetry can be used to obtain a clean measurement of the root-mean-square radius of the neutrons in the 208Pb nucleus. The Z 0 boson couples mainly to neutrons; the neutron weak charge is much larger than that of the proton. The value of this asymmetry is at the sub-ppm level and has a projected experimental fractional precision of 3%. We will describe the accelerator setup used to set controls on helicity-correlated beam asymmetries and the analysis methods for finding the raw asymmetry for HAPPEx-III. We will also discuss in some detail the preparations to meet the experimental challenges associated with measuring such a small asymmetry with the degree of precision required for PREx.

The electric dipole moment of the ground state of cesium, d$\sb{\rm Cs}$, is measured. This result is related to the electric dipole moment of the electron in a straightforward way using the results of atomic theory calculations found in the literature. The resulting limit of the electric dipole moment of the electron represents a stringent test of time reversal invariance. Cesium vapor is studied at zero magnetic field in glass cells which also contain 250 torr of nitrogen. The ground state of cesium is optically pumped by a laser beam and the atomic orientation undergoes the electrical analog of Larmor precession due to an applied electric field. The precession is detected by comparing the transmission rates of left and right circularly polarized light for a second laser beam which is orthogonal to both the initial laser beam and the applied electric field. The Hamiltonians H = $\vec\mu\cdot\vec B$ and H = $\vec d\cdot\vec E$ are interchangeable allowing calibration of the apparatus using an applied magnetic field. During data acquisition all three components of the effective magnetic field are reduced below 100 nG. Comparing signals from two cells with opposite electric fields eliminates signals due to drifts in the homogeneous magnetic field. Comparing the signals from four cells, two with electric fields and two without, reduces noise due to fluctuating magnetic fields to about 150 pG in 20 seconds of integration (a single data point.) The precession frequency is determined with a statistical precision of 0.5 $\mu$Hz in a two day data collection run. A set of 13 data runs, 9 in the two cell configuration and 4 in the four cell configuration, is used to place upper limits d$\sb{\rm Cs}$ $<$ 1.1 $\times$ 10$\sp{-24}$e-cm, d$\sb{\rm e}$ $<$ 9.3 $\times$ 10$\sp{-27}$e-cm and a limit on T-violating electron-nucleon scaler interactions of C$\sb{\rm S}$ $<$ 10$\sp{-5}\rm G\sb{\rm F}$. This limit represents an order of magnitude improvement over the previously limits on d$\sb{\rm Cs}$ and constrains theories attempting to explain the violation of CP invariance which is seen in the K meson system.

We present original calculations of standard model processes involving two weak bosons at NLO in QCD, and study related phenomenology with reference to Higgs boson and new physics searches at the LHC. We employ a new theoretical technique, D-dimensional generalised unitarity, to obtain the multi-particle, one-loop scattering amplitudes for the processes pp → W⁺W^- + 1j, pp → W⁺W^- + 2j, pp → W⁺W⁺ + 2j, and gg → W⁺W^-g. We consider the LHC phenomenology of: the W⁺W^- + n jets background to Higgs searches, for n = 0,1,2; the effects of anomalous tri-linear gauge couplings in WW and WZ production; the background W⁺W⁺ + 2j to new physics searches involving like-sign leptons; and a method of spin determination of new states in a scenario where conventional methods fail.

The International Linear Collider (ILC) aims to collide electrons and positrons with a centre of mass energy of 500GeV and a luminosity of 2×10³⁴ cm⁻² s⁻¹. To achieve this luminosity, the nominal final emittance of the electron and positron beams have to be below 10μm.rad horizontally and 0.04&mu;m.rad vertically. To prevent the emittance from becoming too large, the main linacs will require alignment at an unprecedented level. The ILC main linacs will be aligned with respect to a reference network which runs along the entire length of the tunnel. The Linear Collider Alignment and Survey (LiCAS) Rapid Tunnel Reference Surveyor (RTRS) is the prototype of a device proposed to survey the ILC reference network. The LiCAS RTRS has several measurement systems; its Frequency Scanning Interferometry (FSI) measurement system is studied in this thesis. The FSI system has three distinct sub-systems: the reference interferometers, the external FSI measurement system and the internal FSI measurement system. The errors on the length of the reference interferometers are shown to be of the order of 1.1μm (0.3ppm). The external FSI measurement system is shown to measure distances close to 0.42m with errors of &pm;1.9&mu;m stat &pm;0.16&mu;m syst and the internal FSI measurement system is shown to measure distances close to 4.2m with errors of &pm;0.24&mu;m stat &pm;1.6&mu;m syst. A survey of the ILC reference network using laser trackers is simulated without taking account of systematic measurement errors from refraction in the tunnel air. The simulated networks are used to misalign the simulated accelerators in Dispersion Matched Steering (DMS) simulations. The DMS simulations show that only 30% of the simulated accelerators produce an acceptable final corrected vertical emittance. It is further shown that the introduction of long range distance measurements between primary reference markers (PRMs) using GPS, reduces the long range error growth in the network, and that 95% of simulated accelerators give acceptable performance. A simplified network simulation model, which is capable of simulating reference networks surveyed by conventional and novel devices, is produced and compares favorably to full simulations.

This thesis presents measurements of inclusive and differential cross-sections for top quark pair-production in fiducial and full phase-space regions, as well as an analysis of gas compositions in the ATLAS inner detector cooling systems. The inclusive top-anti-top quark production cross-section was measured using a sample of 0.085 1/fb of proton--proton collisions recorded by the ATLAS experiment at centre-of-mass energy of 13 TeV, using dilepton top-anti-top quark events with an opposite-sign ee or ÂμÂμ pair in the final state. The numbers of events with exactly one and exactly two jets originating from b-quarks were counted to determine the top-anti-top quark production cross-section . The efficiency to reconstruct and identify a jet as originating from a b-quark from a top quark decay was extracted simultaneously, minimising the associated systematics. The cross-section was measured to be 749 ± 57 (stat.) ± 79 (syst.) ± 74 (lumi.) pb, giving a total relative uncertainty of 16%. The differential top-anti-top quark production production cross-sections were measured using top-anti-top quark events with one electron and one muon of opposite sign electric charge, and at least two jets, one of which was required to be tagged as containing a b-hadron. Initially, the differential cross-sections were measured in a fiducial phase-space region, using an integrated luminosity of 3.2 1/fb of proton--proton data at a centre-of-mass energy of 13 TeV, recorded by the ATLAS experiment in 2015. Subsequently, the single and double differential cross-sections were measured in both a fiducial phase-space region and the full phase-space, using 36.1 1/fb of proton--proton data at 13 TeV, recorded by the ATLAS experiment in 2015 and 2016. The measured differential cross-sections are compared to predictions of next-to-leading order generators matched to parton showers. Custom ultrasonic instruments have been developed for simultaneous monitoring of binary gas mixture and flow in the ATLAS inner detector. These instruments are sensitive to leaks in the cooling systems of the ATLAS inner detector. Software for on- and off-line analysis of these instruments has been developed and proven with the analysis of the cool-down to operation temperature in January 2016.

In this dissertation the parity violating neutron deuteron scattering amplitudes are calculated using pionless effective field theory to leading order. The five low energy parity violating constants present in pionless effective field theory are estimated by matching onto the ``best" values for the parameters of the model by Desplanques, Donoghue, and Holstein (DDH). Using these estimates and the calculated amplitudes, predictions for the spin rotation of a neutron through a deuteron target are given with a value of 1.8 × 10-8 rad cm-1. Also given are the longitudinal analyzing power in neutron deuteron scattering with a polarized neutron yielding 2.2 × 10-8, and a polarized deuteron giving 4.0 × 10-8. These observables are discussed in the broader context of hadronic parity violation and as possible future experiments to determine the values of the five low energy parity violating constant present in pionless effective theory.