Dissertations / Theses on the topic 'String Phenomenologie'

We examine the phenomenological properties of certain heterotic string theories through the computation of one and two-loop amplitudes. Initially, we consider the fate of shift-symmetries in effective string models is considered beyond tree-level. Such symmetries have been proposed in the past as a way to maintain a hierarchically small Higgs mass and also play a role in schemes of cosmological relaxation. It is argued that on general grounds one expects shift-symmetries to be restored in the limit of certain asymmetric compactifications, to all orders in perturbation theory. This behaviour is verified by explicit computation of the Kähler potential to one-loop order. We then turn to the two-loop cosmological constant in non-supersymmetric heterotic strings where two independent criteria are presented that together guarantee its exponential suppression. They are derived by performing calculations in both the full string theory and in its effective field theory, and come respectively from contributions that involve only physical untwisted states, and contributions that include orbifold twisted states. The criteria depend purely on the spectrum and charges, so a model that satisfies them will do so with no fine-tuning. An additional consistency condition (emerging from the so-called separating degeneration limit of the two-loop diagram) is that the one-loop cosmological constant must also be suppressed, by Bose-Fermi degeneracy in the massless spectrum. We comment on the effects of the residual exponentially suppressed one-loop dilaton tadpole, with the conclusion that the remaining instability would be under perturbative control in a generic phenomenological construction. We remark that theories of this kind, that have continued exponential suppression to higher orders, can form the basis for a string implementation of the "naturalness without supersymmetry" idea.

Die vorliegende Arbeit beinhaltet ein einführendes Kapitel über Orbifold-Konstruktionen in dem neben rudimentären Grundlagen bereits speziellere Themen wie Diskrete Torsion und asymmetrische Orbifold-Gruppen behandelt werden. Als Beispiele für Orbifolde werden Kompaktifizierungen auf Tori sowie das asymmetrische T^4/Z(3)^L x Z(3)^R Orbifold behandelt. Danach wird eine allgemein gehaltene Einführung in Orientifolde gegeben, einschließlich des offenen String Sektors samt Chan-Paton Freiheitsgraden. Die darauf folgenden Kapitel 4-7 behandeln von mir durchgeführte Forschungsarbeiten. Kapitel 4 beschäftigt sich mit der Quantisierung des offenen Strings mit linearen Randbedingungen, wie sie bei Strings in elektro-magnetischen Feldern auftreten. Weiterhin wird die Quantisierung der Null- und Impuls-Moden des offenen Strings in Torus-Kompaktifizierungen durchgeführt. Außerdem wird für den Fall allgemeiner konstanter Hintergrund Neveu-Schwarz U(1)-Hintergrundfelder der Kommutator der Stringkoordinaten berechnet. Dieser stützt bisherige Resultate zur Nicht-Kommutativität von offenen Stringtheorien in Neveu-Schwarz Hintergründen. Kapitel 5 gibt, zusammen mit einigen neuen Erkenntnissen, Resultate von [1] über asymmetrische Orientifolde, insbesondere deren D-Branen Inhalt wieder. Kapitel 6 faßt die Veröffentlichung [2] zusammen, in der untersucht wurde, inwieweit sich phänomenolgisch interessante Modelle in Orientifolden von Torus-Kompaktifizierungen finden lassen. Insbesondere tragen die D9-Branen magnetische Flüsse, womit chirale Fermionen im Spektrum auftreten. Die Rechnungen werden größtenteils im gleichwertigen, T-dualen Bild ausgeführt. In diesem ist die Anzahl der chiralen Fermionen durch die topologische Schnittzahl der D-Branen gegeben. Existieren auf Torus-Kompaktifizierungen entweder nur nicht-chirale oder nicht-supersymmetrische Modelle, so lassen sich auf gewissen Orbifolden beide Eigenschaften miteinander vereinbaren. Kapitel 7 behandelt das "sigma Omega"-Orientifold auf einem T^6/Z(4) Orbifold. Als besonders interessantes Beispiel wird ein supersymmetrisches U(4) x U(2)^3_L x U(2)^3_R Modell vorgestellt, daß durch Einschalten geeigneter Hintergrundfelder in der effektiven Niederenergie-Wirkung auf ein Modell gebrochen wird, daß dem MSSM (minimalem supersymmetrischen Standard Modell) sehr ähnlich ist. Dieses Kapitel basiert auf unserer Publikation [3]. Ferner ist der Arbeit ein Anhang beigefügt, der einige der verwendeten Formeln sowie Beweise zu zwei Sätzen enthält, die im Text verwendet wurden.
This thesis contains an introductory chapter on orbifolds. Besides rudimentary basics we discuss more advanced topics like discrete torsion and asymmetric orbifold groups. As examples we investigate torus compactifications and an asymmetric T^4/Z(3)^L x Z(3)^R orbifold. The following chapter explains the foundations of orientifolds, including open strings with Chan-Paton degrees of freedom. Chapters 4-7 present own research. In chapter 4 we quantize open strings with linear boundary conditions, as they show up in electro-magnetic fields. We quantize the zero- and momentum-modes for toroidal compactifications, too. As an application we calculate the commutator of the coordinate fields in the case of general constant Neveu-Schwarz U(1)-field strengths. Thereby we confirm previous results on non-commutativity of open string theories in Neveu-Schwarz backgrounds. Chapter 5 reviews the results of a former publication [1] on asymmetric orientifolds, supplemented by some recent insights in connection with the preceeding chapter. Chapter 6 is a summary of [2]. In this publication we investigated to what extend one can build phenomenologically interesting models from toroidal orientifolds. By turning on magnetic fluxes on D9-branes we induce chiral fermions. Most calculations are performed in an (equivalent) T-dual picture. Here the number of chiral fermions is given by the topological intersection number of D-branes. In orientifolds of toroidal compactifications one obtains either non-chiral or non-supersymmetric orientifold solutions. However both properties can be reconciled in orientifolds that are obtained from specific supersymmetric orbifold compactifications. In chapter 7 we present the "sigma Omega"-Orientifold on a T^6/Z(4) orbifold. As a very attractive example we investigate a supersymmetric U(4) x U(2)^3_L x U(2)^3_R model that is broken to an MSSM-like model by switching on suitable background fields in the low energy effective action. This chapter is based on our publication [3]. The thesis is supplemented by an appendix with formulas applied in the text, as well as proofs to two theorems that were used as well.

We examine one loop amplitudes for open and closed strings in certain D-brane configurations, and investigate the consequences for phenomenology. Initially we consider open strings at D6-brane intersections. We develop techniques for one-loop diagrams. The one-loop propagator of chiral intersection states is calculated exactly and its finiteness is shown to be guaranteed by RR tadpole cancellation. The result is used to demonstrate the expected softening of power law running of Yukawa couplings at the string scale. We also develop methods to calculate arbitrary TV-point functions at one-loop, including those without gauge bosons in the loop. These techniques are also applicable to heterotic orbifold models. One issue of the intersecting D6-brane models is that the Yukawa couplings of the simpler models suffer from the so-called "rank one" problem - there is only a single non-zero mass and no mixing. We consider the one-loop contribution of E2-instantons to Yukawa couplings on intersecting D6-branes, and show that they can provide a solution. In addition they have the potential to provide a geometric explanation for the hierarchies observed in the Yukawa couplings. In order to do this we provide the necessary quantities for instanton calculus in this class of background. We then explore how the IR pathologies of noncommutative field theory are resolved when the theory is realized as open strings in background B-fields: essentially, since the IR singularities are induced by UV/IR mixing, string theory brings them under control in much the same way as it does the uv singularities. We show that at intermediate scales (where the Selberg-Witten limit is a good approximation) the theory reproduces the noncommutative field theory with all the (un)usual features such as UV/IR mixing, but that outside this regime, in the deep infra-red, the theory flows continuously to the commutative theory and normal Wilsoman behaviour is restored. The resulting low energy physics resembles normal commutative physics, but with additional suppressed Lorentz violating operators. We also show that the phenomenon of UV/IR mixing occurs for the graviton as well, with the result that, in configurations where Planck's constant receives a significant one-loop correction (for example brane-induced gravity), the distance scale below which gravity becomes non-Newtonian can be much greater than any compact dimensions.

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.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002.
Includes bibliographical references.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
An experimental study was carried out to map the compositional dependence of electromechanical behavior and ferroelectric phase stability in the barium, zirconium-codoped sodium bismuth titanate (BNBZT) system for barium concentrations up to 18 mol.% and zirconium concentrations up to 4 mol.%. A number of polycrystalline BNBZT samples has been electromechanically tested under applied electric fields of different frequencies (0.2-47 Hz). A novel model of electromechanical response capable of describing both dynamic and static hysteresis for pure and mixed cases of ferroelectric, antiferroelectric, ferroelastic and paraelectric behavior has been developed. Major electromechanical properties of polycrystalline BNBZT have been identified and compositionally mapped. The peak of electromechanical response (d33 = 400 pC/N) has been found at the composition (Bil/2Nal/2)0.93Bao.07Zro.02Tio.9803. The compositional dependence of ferroelectric phase stability has been mapped by means of a Landau type free energy expansion. A nanodomain relaxation mechanism of frequency dependent electromechanical response of BNBZT has been suggested and is supported by optical and transmission electron microscopy.
by Andrey N. Soukhojak.
Ph.D.

This thesis concerns a range of aspects of theoretical physics. It is composed of two parts. In the first part we motivate our line of research, and introduce and discuss the relevant concepts. In the second part, four research papers are collected. The first paper deals with a possible extension of general relativity, namely the recently discovered classically consistent bimetric theory. In this paper we study the behavior of perturbations of the metric(s) around cosmologically viable background solutions. In the second paper, we explore possibilities for particle physics with low-scale supersymmetry. In particular we consider the addition of supersymmetric higher-dimensional operators to the minimal supersymmetric standard model, and study collider phenomenology in this class of models. The third paper deals with a possible extension of the notion of Lie algebras within category theory. Considering Lie algebras as objects in additive symmetric ribbon categories we define the proper Killing form morphism and explore its role towards a structure theory of Lie algebras in this setting. Finally, the last paper is concerned with the computation of string amplitudes in four dimensional models with reduced supersymmetry. In particular, we develop general techniques to compute amplitudes involving gauge bosons and gravitons and explicitly compute the corresponding three- and four-point functions. On the one hand, these results can be used to extract important pieces of the effective actions that string theory dictates, on the other they can be used as a tool to compute the corresponding field theory amplitudes.
Over the last twenty years there have been spectacular observations and experimental achievements in fundamental physics. Nevertheless all the physical phenomena observed so far can still be explained in terms of two old models, namely the Standard Model of particle physics and the ΛCDM cosmological model. These models are based on profoundly different theories, quantum field theory and the general theory of relativity. There are many reasons to believe that the SM and the ΛCDM are effective models, that is they are valid at the energy scales probed so far but need to be extended and generalized to account of phenomena at higher energies. There are several proposals to extend these models and one promising theory that unifies all the fundamental interactions of nature: string theory. With the research documented in this thesis we contribute with four tiny drops to the filling of the fundamental physics research pot. When the pot will be saturated, the next fundamental discovery will take place.

Musical analysis has traditionally been located within the context of musicology. It is therefore an activity usually considered the purview of music scholars rather than practical musicians. The musical analyses produced by music scholars therefore provide us with intellectual understandings of musical works, rather than insights into the experience of listening to or playing music. In this thesis, I will propose that those agents involved in practical music-making can produce insights into musical works that are as valid as the work of traditional music scholarship. I will attempt to re-conceptualize the position of the ‘knower’ or ‘experiencer’ - the performer - of music as one with primary access to knowledge of a musical work, and therefore ideally suited to offer analyses of these works. The establishment of the performer as a bearer of central analytical knowledge functions in direct opposition to the traditional distinction between ‘theory’ and ‘practice’. My thesis will trace the Platonic origins of the philosophical separation of practice and research, and as an alternative to the traditional separation of practice and research, I shall explore the concept of Practice-Based Research (PBR). My exploration of PBR will be informed by phenomenological approaches to music scholarship. As a field of enquiry which concerns itself with experience, the phenomenology of music suggests that the mind and body of the practitioner are important sources of musical insight. To address this issue, Bourdieu’s notion of habitus will be explored. The habitus will be shown to contain a vast network of socio-cultural codes informing the practitioner’s relationship with the musical work. A central aim of this thesis is to explore the possibilities of using practice-based research as the foundation for the study and analysis of a composition, in order to allow for a deeper understanding of the work by means of the generation and harnessing of practical knowledge. Thus, the theoretical outline of PBR provided in this thesis will be applied to a piece of practical performance-based analysis. As such, an analysis of Mahler’s Quartetsatz will be used as the basis on which to draw knowledge in this project.

Syftet med detta arbete är att utifrån ett fenomenologiskt livsvärldsperspektiv, utforska hur några professionella musiker upplever att de går till väga under sina instuderingsprocesser. För att belysa detta tar arbetet avstamp i följande forskningsfråga: Vilka övningsstrategier beskriver några professionella musiker att de använder sig av när de tillägnar sig ett för dem nytt material? För att uppnå syfte och forskningsfråga har tre kvalitativa intervjuer genomförts med tre professionella musiker. I resultatet framkommer en rad olika strategier vilka sorterats in i fem meningsenheter: Dagliga tekniska övningsstrategier, Noggranna förberedelser, Tidsplanering, Övriga strategier och Strävan efter utveckling. I diskussionen sätts dessa strategier i relation till bakgrundslitteratur och forskning samt till fenomenologi.
Syftet med detta arbete är att utifrån ett fenomenologiskt livsvärldsperspektiv, utforska hur några professionella musiker upplever att de går till väga under sina instuderingsprocesser. För att belysa detta tar arbetet avstamp i följande forskningsfråga: Vilka övningsstrategier beskriver några professionella musiker att de använder sig av när de tillägnar sig ett för dem nytt material? För att uppnå syfte och forskningsfråga har tre kvalitativa intervjuer genomförts med tre professionella musiker. I resultatet framkommer en rad olika strategier vilka sorterats in i fem meningsenheter: Dagliga tekniska övningsstrategier, Noggranna förberedelser, Tidsplanering, Övriga strategier och Strävan efter utveckling. I diskussionen sätts dessa strategier i relation till bakgrundslitteratur och forskning samt till fenomenologi.

This study examined the perceptions of teachers on the picket line and in the classroom during the 1978 Tucson Unified School District teacher strike and the perceptions and relationships they experienced. Literature from sociology, psychology and education was reviewed to develop the theoretical framework. It is recognized in the literature that theory has utility in designing, shaping and organizing research, giving meaning to data and summarizing and interpreting the findings. The theoretical framework was comprised of two sections: the perceptual and the relational. In the perceptual, self-adequacy, self-concept and threat-anxiety were included. In the relational, communication, shared interests and reference groups were included. An interview schedule of twenty-one items based on the theoretical framework was developed and administered to forty selected school district teachers. The twenty-one questions were derived from the two major sections and the six subsections of the theoretical framework. Some demographic data were also collected. Strikers and non-strikers agreed more than they disagreed. There was general agreement among both strikers and non-strikers that human relationships were handled so ineptly by the superintendent and school board that the teachers perceived themselves to be demeaned and held unworthy.

String theory is at the moment our best candidate for a unified quantum theory of gravity, aiming to reconcile all the known (and unknown) interactions with gravity as well as provide insights for currently mysterious phenomena that the Standard Model and the modern Cosmology are not able to explain. In fact, it is believed that most of the problems associated to the Standard Model can indeed be resolved in string theory. Supersymmetry is supposed to be an elegant solution to the Hierarchy problem (even though more and more stringent bounds in this direction are being placed by the fact that we have been unable to experimentally find supersymmetry yet), while all the axions that compactifications bring into play can be used to resolve the strong CP problem as well as provide good candidates for Dark Matter. Inflationary models can also be constructed in string theory, providing, then, the most diffused solution to the Horizon problem. This work, in particular, is formulated in type IIB string theory compactified on an orientifolded Calabi-Yau three-fold in LARGE Volume Scenario (LVS) and focuses on the stabilisation of all the moduli in play compatible with the construction of a hidden gauge sector whose gauge boson kinetically mixes to the visible sector U(1), acquiring a mass via a completely stringy process resulting in the St{\"u}ckelberg mechanism. The "compatibility" regards the fact that certain experimental bounds should be respected combined with recent data extrapolated by Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) events at the Spallation Neutron Source at Oak Ridge National Laboratory. We are going to see that in this context we will be able to fix all the moduli as well as present a brane and fluxes set-up reproducing the correct mass and coupling of the hidden gauge boson. We also get a TeV scale supersymmetry, since the gravitino in this model will be of order O(TeV), with an uplifted vacuum to reproduce a de Sitter universe as well.

Acompanha: Oficina de luteria e laboratório de acústica: guia adidático
Como é a relação entre acústica e luteria? Tal pergunta é a que se faz o pesquisador ao início da escrita desta dissertação. Mesma pergunta que faz para cinco professores envolvidos com ensino de luteria, participantes da formação do luthier em cursos de duas instituições brasileiras. Esta pesquisa, diante da questão central, tem como objetivo delinear contribuições para esclarecer e favorecer a relação entre luteria e acústica desvelada na perspectiva de ser-luthier, em experiência e compreensão. Através de um estudo de campo, voltou o olhar para a comunidade formada por professores e estudantes ligados à acústica e luteria, particularmente, nas duas instituições brasileiras, sendo que numa delas o pesquisador se colocou como observador participante. Realizou entrevistas com os professores nas duas instituições. Numa delas, especificamente, participou em sala de aula como professor. Assim, tomou contato com reverberações imediatas da atividade didática nos estudantes em formação como luthiers. Antes da entrada em sala e aula, renovava a perspectiva como professor enquanto elaborava uma estratégia didática para favorecer a relação. Para isto, considerou experiências em campo e base na invenção de uma Ilha de Interdisciplinar de Racionalidade de Gérard Fourez, assim como na Teoria das Situações Didáticas de Guy Brousseau, principalmente, sob a noção de situações adidáticas. Os discursos dos entrevistados foram compreendidos através de uma das maiores lições da fenomenologia, a redução fenomenológica. O pesquisador buscou desvelar o fenômeno (antes estruturado para sua consciência) na descrição de cada entrevistado, ao que contribuíram as experiências em campo. Ao fim, desvelou a relação entre acústica e luteria na perspectiva do ser-luthier. Encontrava as próprias possibilidades de vir a ser luthier. Em conclusão do captado com a pesquisa, uma separação apareceu entre acústica e luteria, como um muro impedindo sua relação. Porém, ao perscrutar a essência através da consciência pura da relação (destituída de preconceitos, limitações, predefinições), o muro apareceu insustentável. A relação está nos fundamentos basais da prática da luteria, que tem a acústica como parte indispensável da formação do luthier. Precisa ser reencontrada no enfrentamento dos desafios da prática, sem ludibriá-los através da estética visual e de modelos predefinidos. Ao mesmo tempo, dependerá da superação dos obstáculos interpostos ao confrontar os desafios, contanto com a colaboração entre diversas perspectivas, bem como com a comunicação e compartilhamento aberto de informações. A reflexão sobre as ações didáticas do pesquisador e pela própria redução fenomenológica foi constante. Dela, emergiu um caminho para favorecer a relação entre acústica e luteria. O produto final das experiências e reflexões aparece no Guia Adidático que acompanha esta dissertação.
How is the relation between acoustics and lutherie? The researcher asks himself this question at the beginning of the dissertation, the same that directs to five teachers involved in lutherie teaching, participants in the luthier formation in courses of two Brazilian institutions. This research, from the initial question, aims to delineate contributions to clarify and favor the relation between lutherie and acoustics unveiled in the perspective of the being that takes it in experience and understanding. Delineated as a field study, looks inside a community formed by teachers and students correlated to acoustics and lutherie, particularly in the two Brazilian institutions. In one institution the researchers becomes a participant observer, where conducts interviews with five teachers in both institutions. In one of them, specifically, toked participant observation in classroom. So takes contact with effects of the immediate implications of (your and by others teachers) didactic's activities on students of lutherie. Concomitantly, developed a didactic strategy to favor the relation between acoustics and lutherie, considering experiences in the field and reasoned in the Interdisciplinary Island of Rationality of Gérard Fourez, as well as Theory of the Didactic Situations of Guy Brousseau, especially the concept of adidactic situation. The discourses of the interviewers are understood through one of the greatest lessons of phenomenology, the phenomenological reduction. The researcher sets out to unveil the phenomenon, previously structured for him, to which the experiences in the field contribute. At the end, the relation between acoustics and lutherie is revealed in being-luthier perspective. Also as a becoming-luthier, taking part in the possibility luthier formation. By field study and the phenomenological reduction, a separation was shown between acoustic and lutherie as a wall blocking the relation. However, inside pure consciousness of relation (leaving of prejudice, limitation, determinism), the wall seemed unsustainable. The relation is in basal foundations for practice lutherie, that take the acoustic how indispensable component of luthier formation. Need to be rediscovered through facing practice’s challenges, without cod them by aesthetics and predefined templates. At same time, will depend overcoming obstacles step in practice, counting on collaboration by others perspectives, as well with open communication and sharing information. In the constant reflection of the didactic actions of the researcher, from the beginning to end of the research, he elaborates and re-elaborates didactic's activities. The experiences and reflections conform an Adidactic Guide, as technical production parallel to present dissertation.

During face-to-face meetings, humans use multimodal information, including verbal information, visual information, body language, facial expressions, and other non-verbal gestures. In contrast, during computer-mediated-communication (CMC), humans rely either on mono-modal information such as text-only, voice-only, or video-only or on bi-modal information by using audiovisual modalities such as video teleconferencing. Psychologically, the difference between the two lies in the level of the subjective experience of presence, where people perceive a reduced feeling of presence in the case of CMC. Despite the current advancements in CMC, it is still far from face-to-face communication, especially in terms of the experience of presence. This thesis aims to introduce new concepts, theories, and technologies for presence design where the core is actions for creating presence. Thus, the contribution of the thesis can be divided into a technical contribution and a knowledge contribution. Technically, this thesis details novel technologies for improving presence experience during mediated communication (video teleconferencing). The proposed technologies include action robots (including a telepresence mechatronic robot (TEBoT) and a face robot), embodied control techniques (head orientation modeling and virtual reality headset based collaboration), and face reconstruction/retrieval algorithms. The introduced technologies enable action possibilities and embodied interactions that improve the presence experience between the distantly located participants. The novel setups were put into real experimental scenarios, and the well-known social, spatial, and gaze related problems were analyzed. The developed technologies and the results of the experiments led to the knowledge contribution of this thesis. In terms of knowledge contribution, this thesis presents a more general theoretical conceptual framework for mediated communication technologies. This conceptual framework can guide telepresence researchers toward the development of appropriate technologies for mediated communication applications. Furthermore, this thesis also presents a novel strong concept – presence through actions - that brings in philosophical understandings for developing presence- related technologies. The strong concept - presence through actions is an intermediate-level knowledge that proposes a new way of creating and developing future 'presence artifacts'. Presence- through actions is an action-oriented phenomenological approach to presence that differs from traditional immersive presence approaches that are based (implicitly) on rationalist, internalist views.

The low-energy supersymmetry phenomenology for specific classes of string compactifications is investigated given that the low-energy physics may provide a clue as to the structure of the fundamental theory at high energy scales. The one-parameter model (OPM), a highly constrained subset of minimal Supergravity where all the soft-supersymmetry breaking terms may be fixed in terms of the gaugino mass, is studied, in addition to a three-family Pati-Salam model constructed from intersecting D6-branes. Furthermore, the phenomenology of gravity mediated supersymmetry breaking F-theory SU(5) and SO(10) models, as well as F-SU(5) models with vector- like particles, are examined. We determine the viable parameter space that satisfies all the latest experimental constraints, including the most recent WMAP relic neutralino abundance observations, and find it to be consistent with the CDMS II and other concurrent direct-detection experiments. Moreover, we compute the gamma-ray flux and cross-sections of neutralino annihilations into gamma-rays and compare to the published Fermi-LAT satellite telescope measurements. In F-theory SU(5) and SO(10) models, we predict the exact small deviation of the gaugino mass relation at two-loop level near the electroweak scale, which can be tested at the colliders. More- over, in F-SU(5), we predict the precise deviations from the mSUGRA gaugino mass relations due to the presence of the vector-like particles, also testable at the colliders. The compilation of all these results form a comprehensive collection of predictions with which to evaluate these string models alongside anticipated experimental dis- coveries in the coming decade.

abstract: In this dissertation, I present the results from my recent investigations into the interactions involving topological defects, such as magnetic monopoles and strings, that may have been produced in the early universe. I performed numerical studies on the interactions of twisted monopole-antimonopole pairs in the 't Hooft-Polyakov model for a range of values of the scalar to vector mass ratio. Sphaleron solution predicted by Taubes was recovered, and I mapped out its energy and size as functions of parameters. I also looked into the production, and decay modes of $U(1)$ gauge and global strings. I demonstrated that strings can be produced upon evolution of gauge wavepackets defined within a certain region of parameter space. The numerical exploration of the decay modes of cosmic string loops led to the conclusions that string loops emit particle radiation primarily due to kink collisions, and that their decay time due to these losses is proportional to $L^p$, where $L$ is the loop length and $p \approx 2$. In contrast, the decay time due to gravitational radiation scales in proportion to $L$, and I concluded that particle emission is the primary energy loss mechanism for loops smaller than a critical length scale, while gravitational losses dominate for larger loops. In addition, I analyzed the decay of cosmic global string loops due to radiation of Goldstone bosons and massive scalar ($\chi$) particles. The length of loops I studied ranges from 200-1000 times the width of the string core. I found that the lifetime of a loop is approximately $1.4L$. The energy spectrum of Goldstone boson radiation has a $k^{-1}$ fall off, where $k$ is the wavenumber, and a sharp peak at $k\approx m_\chi/2$, where $m_\chi$ is the mass of $\chi$. The latter is a new feature and implies a peak at high energies (MeV-GeV) in the cosmological distribution of QCD axions.
Dissertation/Thesis
Doctoral Dissertation Physics 2020

Romanian composer Iancu Dumitrescu began writing music in the late 1960s and early 1970s and has enjoyed a successful career in his home country, albeit one with limited exposure in the English-speaking world. The collapse of communism and the fall of the Romanian regime in 1989 sparked a new and revitalized era in Dumitrescu's career that has culminated in numerous features in prominent music magazines such as Musicworks and The Wire. Until now, however, there has been no serious analysis of Dumitrescu's music and his philosophically inspired techniques of composition. Often described as a member of the Romanian spectral school alongside the likes of Horatiu Radulescu and Octavian Nemescu, Dumitrescu is also known for his interest in the phenomenology of Edmund Husserl. In this thesis I analyze two of Iancu Dumitrescu's chamber works for strings, Alternances (1&2) (1967) and Movemur et Sumus (3) (1977).