Superstring theory posits that as complicated as nature may seem to the naive observer, the variety of observed phenomena may be explained by postulating that at the fundamental scale, matter is composed of lines of energy, namely strings. These oscillating lines would be elementary and would hence have no substructure. They are expected to be incredibly tiny, their line-like structure would become noticeable at scales close to the string scale (which may lie anywhere from the TeV scale all the way up to the Planck scale) and would appear to be point-like to the macroscopic observer. Internal consistency then also requires the presence of higher dimensional objects, namely D-branes, all of which conspire and combine in such a way so as to give rise to the observable Universe. Advances in cosmology suggest the early universe was much hotter and denser than is the Universe at present, that the Universe has expanded and continues to expand (exponentially in fact) at present. This in turn has led a number of theorists to point out the remarkable possibility that some of these strings or D-branes were also stretched with the expansion. The resulting macroscopic strings, the so-called cosmic strings, would potentially stretch across the entire Universe. Cosmic strings make their presence manifest by oscillating, scattering off other structures, by decaying, producing gravitational waves and so on, and this in turn hints at the available handles that may be used to observe them. Before we can hope to observe cosmic strings however, the first step is then clearly to understand these properties which determine their evolution. A number of approximate (classical) descriptions of cosmic strings have been constructed to date, but approximations break down, especially when potentially interesting things happen (e.g. close to cusps, i.e. points on the string that reach the speed of light) and can obscure the physics. Thankfully, one can go beyond these approximations: all properties of cosmic strings can be concisely and accurately contained or encoded in a single object, the so-called fundamental cosmic string vertex operator. In the present thesis I construct precisely this, covariant vertex operators for general cosmic strings and this is the first such construction. Cosmic strings, being macroscopic, are likely to exhibit classical behaviour in which case they would most accurately be described by a string theory analogue of the well known harmonic oscillator coherent states. By minimally extending the standard definition of coherent states, so as to include the string theory requirements, I go on to construct both open and closed covariant coherent state vertex operators. The naive construction of the latter requires the existence of a lightlike compactification of spacetime. When the lightlike winding states in the underlying Hilbert space are projected out, the resulting vertex operators have a classical interpretation and can consistently propagate in noncompact spacetime. Using the DDF map I identify explicitly the corresponding general lightcone gauge classical solutions around which the exact macroscopic quantum states are fluctuating. We go on to show that both the covariant gauge coherent vertex operators, the corresponding lightcone gauge coherent states and the classical solutions all share the same mass and angular momenta, which leads us to conjecture that the covariant and lightcone gauge states are different manifestations of the same state and share identical interactions. Apart from the coherent state vertices I also present a complete set of covariant mass eigenstate vertex operators and these may also be relevant in cosmic string evolution. Finally, I also present the first amplitude computation with the coherent states, the graviton emission amplitude (including the effects of gravitational backreaction) for a simple class of cosmic string loops. As a byproduct of the above, I find that the fundamental building blocks of arbitrarily massive covariant string states are given by elementary Schur polynomials (equivalently complete Bell polynomials). This construction enables one to address the aforementioned questions concerning the properties of cosmic strings, their cosmological signatures, and may lead to the first observations of such objects in the sky. This in turn would be a remarkable way of verifying Superstring theory as the framework underlying the structure of our Universe.

This thesis aims to give an approach to dealing with Hierarchy problems in theoretical physics, plaguing theories that span a wide range of energy scales. At present, any theory that is formulated to connect observations of the Early Universe to results in present day particle physics, exhibits the necessity of (at least one) unnaturally fine-tuned parameter. This has encouraged the sectioning of of many separate, highly specialized fields - each dealing with Effective Field Theories (EFTs) valid at a limited range of energy scales only. Here I describe an effort to connect different energy scales while dynamically accounting for hierarchies. This thesis discusses the appeal of pseudo-Goldstone bosons (pGBs) for the generation of scales in Early Universe cosmology. In particular, I will show how models with pGBs address the radiative instability of mass scales in quantum mechanical theories. I will start with an introduction to the two hierarchy problems that will be the primary focus of the thesis: the electroweak hierarchy problem, or the puzzle of the lightness of the Higgs mass; and the inflationary hierarchy problem, or the flatness of the inflaton potential demanded by the nearly scale invariant spectrum of the Cosmic Microwave Background. I will briefly introduce how pGBs arise, and can be described, using an example of a compact Special Orthogonal group SO(n) breaking to its largest coset SO(n - 1). I will then explore various models that address the electroweak and the inflationary hierarchy problem, using appropriate EFT tools such as the Callan-Coleman-Wess-Zumino mechanism and 5D approaches. I will discuss the relative strength of these models compared to existing models in the literature. After this discussion I will show that it is possible to address both hierarchy problems in a unified model, in which an inflaton decays into the Higgs field after inflation, in a process called reheating. This section will include a detailed derivation of the model, and will explore the regions of parameter space that lead to inflation, reheating, and electroweak symmetry breaking compatible with the relevant experimental data. This is followed by an excursion in which I will discuss non-compact models, based on SO(n;1)=SO(n) cosets. I will show how such setups can also give rise to inflation compatible with the current data, and discuss different scenarios for reheating. I will finish with an epilogue of the prospects of (holographic) Composite Higgs models - in which the Higgs is a pGB of the breaking of a strong compact symmetry - at particle colliders.

"January 2002." / Bibliography: p. 147-152. / x, 152 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 2002

Investigations of the cosmic ray flux around the " knee " in the all - particle energy spectrum can provide information on the origin of this steepening. Studies of air shower development in this region are especially informative, although experiments in recent years have produced some conflicting results. Some report an unusually rapid development of showers, which has been interpreted in terms of an increased proportion of heavy nuclei in the flux, compared with the directly measured low energy composition. This thesis describes measurements of the lateral distribution of Cerenkov light associated with air showers with sea level sizes between ~ 10 ^ and 1O7 particles. It is shown that the slope of the lateral distribution is sensitive to air shower development and that the shape is in agreement with the results of recent calculations. These calculations are used to assign depths of maximum to the showers observed. A comprehensive simulation of the selection biases present in the experiment is used in the interpretation of the results on the depth of shower maximum. The data are shown to be consistent with a cosmic ray composition rich in iron in the energy region studied. / Thesis (Ph.D.)--Department of Physics, 1985.

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Thomas K. Gaisser, Dept. of Physics & Astronomy. Includes bibliographical references.

Despite many years of research dedicated to elucidating the conditions in which cosmic rays (CRs) are accelerated, there is still great uncertainty about exactly how such particles are accelerated up to energies of 1 TeV (1 TeV= 10¹² eV) and well beyond. Additionally, there is also great uncertainty about the structure and amplitude of the Galactic magnetic field which necessarily has a great impact upon the movement and interaction of CRs in the Galaxy. This thesis deals with a number of ways in which Gigahertz (GHz) frequency radio continuum observations can be used with GeV–TeV γ-ray observations to explore (i) the CR spectrum and (ii) the magnetic field amplitude in the Galaxy. An accurate knowledge of the CR spectrum and amplitude of the magnetic field has important consequences for a wide range of phenomena, such as particle acceleration and even star formation within the Galaxy. We present a simple static, single-zone model of secondary electron and positron production from CR protons and heavier nuclei interacting with ambient matter. We then apply this model, assuming a local CR spectrum, to predict the synchrotron emission from two cold, dense, massive molecular cores which are relatively nearby using a prescription for the magnetic field which scales as the (approximate) square-root of the hydrogen number density. Radio continuum observations with the Australia Telescope Compact Array (ATCA) are then used to search for this emission and, due to the lack of detection, upper limits to the magnetic fields within these cores are obtained. We find that these limits are not inconsistent with the prescription used in the theoretical modeling. We also present observations of a giant molecular cloud located in the Galactic centre (GC) region, Sagittarius B2 (Sgr B2), chosen because of the expectation of a higher CR flux (than that observed at the top of the earth’s atmosphere). Based on previous work, the simple model presented in this thesis is then extended to include effects of CR diffusion into the Sgr B2 cloud parameterized by a “diffusion transport suppression” factor (and based on a molecular distribution – obtained from NH₃ spectral line emission studies – that can modeled as a three-dimensional Gaussian distribution). Our results show that the complex nature of the environment severely hampers the separation of the thermal and non-thermal emission so that no spectral, polarized or morphological evidence is found for non-thermal emission due to secondary electrons and positrons. Analysis of the radial brightness distribution from the centre of the main complex of Sgr B2 allowed us to place limits on the diffusion of GeV energy CRs into the cloud. This leads to a relative deficit of CRs at the centre of the cloud and a morphology which is reminiscent of a ‘limb-brightening’ of synchrotron emission from secondary electrons and positrons. This is in contrast to to the TeV energy γ-rays from which a good correlation with molecular matter in the GC region is observed. This is interpreted by us as evidence of the exclusion of GeV energy CRs from the densest molecular environments in this region, whilst the TeV (or higher) CRs are able to freely penetrate these regions leading to the γ-ray -molecular line emission correlation observed by the HESS telescopes. Serendipitously, observations of this region uncovered evidence of non-thermal emission from a source to the south of the main complex of emission within Sgr B2. Analysis of archival XMM-Newton X-ray observations revealed an X-ray source located approximately 20” from the non-thermal radio source whose spectrum is strongly suggestive of a SNR. The non-thermal radio spectrum, X-ray source and spectrum were then used in concert with NH3 line emission to argue that this source is a SNR of approximately 3000 years of age which had exploded in this dense region. A large gradient in the NH₃ line emission towards the X-ray source suggests that any SNR shell would expand towards this region of lower density. Analysis of higher resolution 1720 MHz ATCA data revealed a weak source whose extension is coincident with the X-ray source. Finally, the observations of the Sgr B2 region were then expanded to explore the nature of the magnetic field amplitude on large scales in the region, of which there is a two orders of- magnitude uncertainty. Based on earlier work, which showed a large (6° x 2°) region of synchrotron emission at the GC, we assembled single-dish and interferometric observations of this region. The objective of this was to explore the possibility that a ‘spectral downturn’ existed at GHz frequencies, which is due to the gradual dominance towards lower energies of the bremsstrahlung cooling rate over the synchrotron cooling rate. After the removal of appropriate background and the consideration of limitations at GeV and TeV energies, we found significant statistical evidence for a spectral break at ~ 2 GHz, which implies a magnetic field amplitude of 100 μG in a density of ~ 100 cm ⁻³. An amplitude this high, on such large scales will have a large impact on processes such as particle acceleration, star-formation and gas-dynamics in the region. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1456598 / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2009

Software size measurement provides a basis for software project management and plays an important role for its activities such as project management estimations, process benchmarking, and quality control. As size can be measured with functional size measurement (FSM) methods in the early phases of the software projects, functionality is one of the most frequently used metric. On the other hand, FSMs are being criticized by being subjective. The main aim of this thesis is increasing the accuracy of the measurements, by decreasing the number of defects concerning FSMs that are measured by COSMIC FSM method. For this purpose, an approach that allows detecting defects of FSMs automatically is developed. During the development of the approach, first of all error classifications are established. To detect defects of COSMIC FSMs automatically, COSMIC FSM Defect Detection Approach (DDA) is proposed. Later, based on the proposed approach, COSMIC FSM DDT (DDT) is developed.

Thesis--M. Phil., University of Hong Kong, 1983.

Thesis--Ph. D., University of Hong Kong.

published_or_final_version / Physics / Master / Master of Philosophy