The UCNA Experiment at the Los Alamos Neutron Science Center (LANSCE) uses an electron spectrometer to observe angular correlations between the neutron spin and the momenta of β particles emitted during the process of β decay. These angular correlations give rise to an asymmetry determined by the ratio of two coupling constants, gA and gV . Combined with neutron lifetime measurements, these observations probe physics beyond the standard model through unitarity tests of the Cabbibo-Kobayashi-Maskawa Matrix. UCNA’s current spectrometer uses a multi-wire proportional chamber and a plastic scintillator coupled to four photomultiplier tubes (PMTs) by 2 meters of light guides to record energy, position, and time data. The UCNA Collaboration is exploring ways to modernize the detector package using silicon photomultipliers (SiPMs) to increase the sensitivity of the experiment. The new configuration of the spectrometer is expected to improve systematic uncertainties; namely the 2 meter path the produced light must travel to reach the PMTs and the SiPMs’ quantum efficiency being a factor of 2 greater than the prior PMTs’. The subject of this paper is a prototype detector for evaluating the SiPMs as the only detectors present, the goal being to compare the position and energy resolution with that of the current spectrometer in use at UCNA.

A non-supersymmetric Yi-deformed AdS/CFT correspondence has recently been conjectured by Frolov. A detailed description of both sides of this proposed gauge/string duality is presented. The analogy that exists between single trace gauge theory operators in the SU(3) sector and i-deformed SU(3) integrable spin chains is also discussed. Frolov, Roiban and Tseytlin’s leading order comparison between the ideformed spin chain coherent state action and i-deformed string worldsheet action in the semiclassical limit is reviewed. A particular Lax pair representation for the first order semiclassical i-deformed spin chain/string action is then constructed.

In this thesis the close relationship between the topological $K$-homology group of the spacetime manifold $X$ of string theory and D-branes in string theory is examined. An element of the $K$-homology group is given by an equivalence class of $K$-cycles $[M,E,\phi]$, where $M$ is a closed spin$^c$ manifold, $E$ is a complex vector bundle over $M$, and $\phi: M\rightarrow X$ is a continuous map. It is proposed that a $K$-cycle $[M,E,\phi]$ represents a D-brane configuration wrapping the subspace $\phi(M)$. As a consequence, the $K$-homology element defined by $[M,E,\phi]$ represents a class of D-brane configurations that have the same physical charge. Furthermore, the $K$-cycle representation of D-branes resembles the modern way of characterizing fundamental strings, in which the strings are represented as two-dimensional surfaces with maps into the spacetime manifold. This classification of D-branes also suggests the possibility of physically interpreting D-branes wrapping singular subspaces of spacetime, enlarging the known types of singularities that string theory can cope with. / Master of Science

This thesis explores three different aspects of quantum gravity. First we study D3-brane black holes in Calabi-Yau compactifications of type IIB string theory. Using the OSV conjecture and a relation between topological strings and matrix models we show that some black holes have a matrix model description. This is the case if the attractor mechanism fixes the internal geometry to a conifold at the black hole horizon. We also consider black holes in a flux compactification and compare the effects of the black holes and fluxes on the internal geometry. We find that the fluxes dominate. Second, we study the scalar potential of type IIB flux compactifications. We demonstrate that monodromies of the internal geometry imply as a general feature the existence of long series of continuously connected minima. This allows for the embedding of scenarios such as chain inflation and resonance tunneling into string theory. The concept of monodromies is also extended to include geometric transitions: passing to a different Calabi-Yau topology, performing its monodromies and then returning to the original space allows for novel transformations. All constructions are performed explicitly, using both analytical and numerical techniques, in the mirror quintic Calabi-Yau. Third, we study cosmological topologically massive gravity at the chiral point, a prime candidate for quantization of gravity in three dimensions. The prospects of this scenario depend crucially of the stability of the theory. We demonstrate the presence of a negative energy bulk mode that grows logarithmically toward the AdS boundary. The AdS isometry generators have non-unitary matrix representations like in logarithmic CFT, and we propose that the CFT dual for this theory is logarithmic. In a complementing canonical analysis we also demonstrate the existence of this bulk degree of freedom, and we present consistent boundary conditions encompassing the new mode.

<p>The purpose of this thesis is twofold and motivated by recent developments in string theory and extra dimensional models. The first objective is to describe the development and progress in the codimension-2 brane paradigm as a potential cosmological scenario. Secondly, it presents the Antide Sitter/Conformal Field Theory (AdS/CFT) conjecture, also known as holography, as a tool for calculating physical quantities in condensed matter system and goes on to model the quantum Hall effect. We first describe the initial development of treating back-reaction in codimension-2 branes systems with a scalar and gauge field. The purpose of this is to examine the low-energy effective dynamics on the brane. Furthermore, applications are then explored for D7-branes in F-theory as well as D3-branes in large extra dimensional scenarios explored as a model for the cosmological constant problem. The result of this work is that the higher and lower dimensional scenarios are consistent with each other once brane back-reaction is considered in these models. This work led to a number of future works one of which is in relation to the cosmological constant problem. While the subsequent work is beyond the scope of this thesis, we present a picture and further references for the reader. The larger, later, portion of this thesis introduces the concept of holography, its origins, and the applicability to condensed matter systems. Furthermore, we discuss the applicability in particular to the quantum Hall effect (QHE) and present a model in the holographic language that correctly reproduces some of the physics of the QHE. This includes a paper in which we introduce the model, along with demonstration of symmetry properties and conductivity calculations, as well as a paper which examines the finite size scaling behaviour of the model. As a benefit to the reader, we present a `starter edition guide' to the AdS/CFT dictionary preceding these papers for non-experts such that this thesis is self-contained. The upshot is that these avenues of work, in particular quantum Hall-ography, have been very successful in modeling physics using tools originally developed by string theory. As such, it provides support for string theory as a model and framework, as well as providing more opportunities for future predictions of physical quantities.</p> / Doctor of Philosophy (PhD)

<p>We consider the phenomenology of the Magnetic Inelastic Dark Matter model, specifically its capture and subsequent annihilation in the Sun. By using the most recent data from the IceCube and Super- Kamiokande neutrino detection experiments, we are able to put limits on the dipole moment of this WIMP candidate for masses ranging from 100 GeV to 10 TeV with a mass-splitting ranging from 0 to 200 keV. Limits are placed on a 100 GeV WIMP with magnetic dipole interactions as low as 2.6 × 10^−6µN for an inelastic parameter of 100 keV</p> / Master of Science (MSc)

<p>String theory is a unified framework for general relativity and quantum mechanics, thus being a theory of quantum gravity. In this thesis we discuss various aspects of quantum gravity for particular systems, having in common the existence of horizons. The main motivation is that one major challenge in theoretical physics today is in trying to understanding how time dependent backgrounds, with its resulting horizons and space-like singularities, should be described in a controlled way. One such system of particular importance is our own universe.</p><p>We begin by discussing the information puzzle in de Sitter space and consequences thereof. A typical time-scale is encountered, which we interpreted as setting the thermalization time for the system. Then the question of closed time-like curves is discussed in the combined setting where we have a rotating black hole in a Gödel-like universe. This gives a unified picture of what previously was considered as independent systems. The last three projects concerns $c=1$ matrix models and their applications. First in relation to the RR-charged two dimensional type 0A black hole. We calculate the ground state energy on both sides of the duality and find a perfect agreement. Finally, we relate the 0A model at self-dual radius to the topological string on the conifold. We find that an intriguing factorization of the theory previously observed for the topological string is also present in the 0A matrix model.</p>

String theory is a unified framework for general relativity and quantum mechanics, thus being a theory of quantum gravity. In this thesis we discuss various aspects of quantum gravity for particular systems, having in common the existence of horizons. The main motivation is that one major challenge in theoretical physics today is in trying to understanding how time dependent backgrounds, with its resulting horizons and space-like singularities, should be described in a controlled way. One such system of particular importance is our own universe. We begin by discussing the information puzzle in de Sitter space and consequences thereof. A typical time-scale is encountered, which we interpreted as setting the thermalization time for the system. Then the question of closed time-like curves is discussed in the combined setting where we have a rotating black hole in a Gödel-like universe. This gives a unified picture of what previously was considered as independent systems. The last three projects concerns $c=1$ matrix models and their applications. First in relation to the RR-charged two dimensional type 0A black hole. We calculate the ground state energy on both sides of the duality and find a perfect agreement. Finally, we relate the 0A model at self-dual radius to the topological string on the conifold. We find that an intriguing factorization of the theory previously observed for the topological string is also present in the 0A matrix model.

In this thesis we employ string perturbation theory in toroidal orbifold models to study aspects of supersymmetry breaking in type IIB string theory. First, we determine the dependence of physical Yukawa couplings on blow-up moduli in models with D3-branes at orbifold singularities. Blow-up moduli are scalar fields describing the size of small blow-up cycles in the compactification geometry. In models implementing moduli stabilisation these fields can acquire F-terms and break supersymmetry. We examine the moduli-dependence of physical Yukawa couplings at string tree-level by computing disk correlation functions involving a Yukawa interaction of visible sector fields and an arbitrary number of blow-up moduli. We perform the calculation for one blow-up insertion explicitly and find that the correlation function vanishes if the blow-up modulus is associated with a small cycle distant to the visible sector. For more than one blow-up insertion we show that all such correlation functions are exponentially suppressed by the compactification volume. We explain how these results are relevant to suppressing soft terms to scales parametrically below the gravitino mass. Further, we determine corrections to holomorphic Yukawa couplings on D3-branes at an orbifold singularity due to non-perturbative effects such as gaugino condensation on a stack of D7-branes. This can be done by calculating a one-loop threshold correction to the gauge coupling on the D7-branes. We show that, if present, the new contributions to Yukawa couplings are not aligned with the tree-level couplings. As the new Yukawa couplings contribute to soft A-terms they are sources of flavour-changing neutral currents. Last we discuss an effect unrelated to supersymmetry breaking. We show that orbifold models with D3-branes at orbifold singularities can exhibit kinetic mixing of different massless Abelian factors. For this to be possible, the relevant U(1) factors have to be associated with more than one orbifold singularity.

<p>For the first time in the history of physics we stand in front of a theory that might actually serve as a unification of it all - string theory. It provides a self-consistent framework for gravity and quantum mechanics, which naturally incorporates matter and gauge interactions of the type seen in the standard model. Unfortunately, at the moment we do not know of any principle that selects the vacuum of the theory, so predictions about our four-dimensional world are still absent. However, the introduction of extended objects opens up an intricate new arena of physics, which is non-trivial and challenging to map out, even at a basic level.</p><p>A key concept of quantum gravity is holography; this is realised in string theory by the AdS/CFT correspondence, which relates string theory to a field theory living in a lower dimensional space. In this thesis we discuss two limits of the correspondence, namely the BMN limit, giving rise to a plane wave geometry, and the tensionless limit, exhibiting massless higher spin interactions. We also study a limit of string theory in a background electric field, where the theory is described by open strings and positively wound closed strings only.</p><p>We begin with a brief review of the theory, focusing on an intuitive understanding of the basic aspects and serving as an introduction to the papers. In the first paper we calculate, from two different points of view, scattering amplitudes in the non-commutative open string limit. In the second paper we obtain the quadratic scalar field contributions to the stress-energy tensor in the minimal bosonic higher spin gauge theory in four dimensions. In the last paper we propose a way to avoid fermion doubling when discretizing the string in the BMN limit.</p>