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Escoda, Cristina. "On type IIB flux compactification and inflation". Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612006.
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Panizo, Daniel. "Type IIB compactifications and string dualities". Thesis, Uppsala universitet, Teoretisk fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-375025.
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In the present thesis, we offer an introduction to type IIB string compactifications on $\mathbb{T}^{d}/\Gamma$ toroidal orbifolds. We first describe the technical method to construct these spaces and reduce the string background on it. We will have (non)-geometrical fluxes arising from these spaces which decorate with discrete deformations our four $\mathcal{N}=1$ dimensional supergravity theory. Solving its equations of motion, we find several families of supersymmetric AdS vacua with fixed moduli, which can be related through a set of $SL(2,\mathbb{Z})$ symmetries.
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Daniel, Panizo. "Review of compact spaces for type IIA/IIB theories and generalised fluxes". Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-384227.
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In the present project we study compactifications of type IIA/IIB string theories on toroidal orbifolds. We present the moduli space for N=1 four-dimensional reductions and its topological properties. To fix the value of all moduli, we will construct the most general holomorphic superpotential W using a set of T-dual iterations for the fluxes. Using a 3-torus toy-model, we will give an introductory description to the background of these generalised fluxes.
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Witkowski, Lukas Thomas. "Sequestering of Kähler moduli in type IIB string theory". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:6f5c8a99-26ca-401b-ad42-7bd3bf873f80.
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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.
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Pajer, Enrico. "Phenomenological aspects of type IIB flux compactifications". Diss., kostenfrei, 2008. http://edoc.ub.uni-muenchen.de/8956/.
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Koers, Simon. "Type IIA Flux Compactifications". Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-104745.
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Bollan, Nicole Edmea. "General analysis of moduli stabilization in type IIB string compactifications". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13498/.
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In the context of type IIB superstring flux-compactifications on Calabi Yau orientifolds, stabilizing the Kähler moduli is crucially challenging due to the tree-level protection arising from the so-called "No-scale structure". The breaking of this no-scale effective symmetry is paramount within the process of moduli stabilization; this work is aimed at studying the ways of a controlled breaking of this effective symmetry using some sub-leading effects such as perturbative α′-corrections to the Kähler potential and non-perturbative effects to the superpotential. The same have led to three attractive and well-established schemes for moduli stabilization, namely the KKLT scheme, the racetrack scheme and the Large Volume Scenarios (LVS) scheme. The main goal for the present work is twofold; first to study the scalar potential for closed-string moduli in a quite model-independent way which will subsequently enable to understand some interesting features of the no-scale structure breaking, second, to provide a unified framework for the above mentioned three well-known schemes for moduli stabilization. Our generic approach not only helps in directly reading-off the scalar potentials of these schemes via merely knowing some topo- logical data (such as intersection numbers) of the compactifying Calabi Yau, but being generic it also provides the hope both for some useful extensions of these schemes and for the possibility of finding a new moduli stabilization scheme, e.g. using odd moduli. Moreover, this approach might ultimately lead to performing a model independent analysis for moduli stabilization, for example via creating the possibility of finding some general conditions for the existence of stable de-Sitter vacua for arbitrary compactifcations, as would be highly desirable.
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Cicoli, Michele. "String loop moduli stabilisation and cosmology in IIB flux compactifications". Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611500.
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Gil, Pedro Francisco M. S. V. "On moduli stabilisation and cosmology in type IIB flux compactifications". Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:6c3ef85d-df3b-42c6-846d-a4bfdeec85de.
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This Thesis studies some aspects of string compactifications with particular em- phasis on moduli stabilisation and cosmology. In Chapter 1 I motivate the study of string compactifications as a way to build on the successes of the Standard Model of Particle Physics and of the theory of General Relativity. Chapter 2 constitutes an overview of the technical background necessary for the study of flux compactifications. I sketch how the desire to obtain a supersymmet- ric theory in four dimensions constrains us to consider compactifications of the ten dimensional theory in six dimensional Calabi-Yau orientifolds. I argue that it is strictly necessary to stabilise the geometry of this compact space in order to have a phenomenologically viable four dimensional theory. I introduce the large volume scenario of type IIB compactifications that successfully incorporates fluxes and sub- leading corrections to yield a four dimensional theory with broken supersymmetry and all geometrical moduli stabilised. The next four Chapters are devoted to the study of some phenomenological aspects of moduli stabilisation and constitute the original work developed for this Thesis. In Chapter 3 I investigate the consequences of field redefinitions in the stabilisation of moduli and supersymmetry breaking, finding that redefinitions of the small blow- up moduli do not significantly alter the standard picture of moduli stabilisation in the large volume scenario and that the soft supersymmetry breaking terms are generated at the scale of the gravitino mass. Chapter 4 deals with the putative destabilisation of the volume modulus by very dense objects. The analysis of the moduli potential shows that even the densest astrophysical objects cannot destabilise the moduli, and that destabilisation is only achievable in the context of black hole formation and cosmological singularities. In Chapter 5 I present a model of inflation within the large volume scenario. The inflaton is identified with a geometric modulus, the fibre modulus, and its potential generated by poly-instanton effects. The model is shown to be robust and consistent with current observational constraints. In Chapter 6 I introduce a model of quintessence, where the quintessence field and its potential share the same origin with the inflationary model of the previous Chapter. This model constitutes a stringy realisation of supersymmetric large extra dimensions, where supersymmetry, the low gravity scale and the scale of dark energy are intrinsically connected. I conclude in Chapter 7 outlining the direction of future research.
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Moster, Sebastian. "Applications of the D-Instanton Calculus in Type IIB Orientifold Compactifications". Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-117592.
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Goi, Enrico. "Quelques aspects de la brisure de supersymétrie en théorie des cordes de types IIA : vides et déformations". Paris 7, 2011. http://www.theses.fr/2011PA077172.
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Cette thèse porte sur l'étude des compactifîcations non-supersymétriques avec flux en théorie des cordes de type IIA. Après une introduction aux théories de type II, nous introduisons le cadre mathématique de la Géométrie Complexe Généralisée, celle ci donne une interprétation géométrique des vides supersymétriques et un principe permettant de les organiser. Nous introduisons la classe des solvmanifolds, qui ont été largement utilisées comme variétés de compactification, et discutons leurs propriétés mathématiques, notament les critères de compacité. Nous présentons ensuite notre premier exemple de compactification non-supersymétrique, un vide qui a pour espace externe un espace de Sitter. Nous résolvons les équations du mouvement et dans le même temps nous discutons le comportement de D-branes dans les fonds non- supersymétriques. Une brève analyse de la physique à quatre dimensions est également fournie. Nous spéculons sur l'utilisation de la Géométrie Généralisée pour les vides non-supersymétriques et sur leur structure géométrique. Motivé par des considérations issues de la dualité AdS/CFT nous analysons un vide non-supersymétrique, censé être le correspondant gravitationnel d'un vide métastable non supersymétrique d'une théorie de jauge supersymétrique. La supersymétrie est ici brisée par l'ajout d' anti-branes, dont il est notoirement difficile de prendre en compte la contre réaction. Ainsi nous avons recours à l'utilisation d'une technique perturbative. Nous calculons les déformations du premier ordre d'un fond D2-brane, discutons l'espace des solutions et argumentons sur la nature des singularités inévitables que nous rencontrons dans le processusThis thesis is devoted to the study of non-supersymmetric flux compactifications in type IIA string theory. After a brief review of type II theories, we introduce the mathematical framework of Generalized Complex Geometry, which provides an encompassing geometric interpretation and organizing principle for supersymmetric vacua. We introduce the class of solvmanifolds, which have been extensively used as compactification manifolds, and discuss their mathematical properties, with particular attention to the compactness criteria. We then present our first example of non-supersymmetric compactification, a vacuum which has a de Sitter external space. We solve the equations of motion and in the process we argue about the behaviour of D-branes in non-supersymmetric backgrounds; a short analysis of the four dimensional physics is also provided. We speculate about the use of Generalized Geometry for non-supersymmetric vacua too and about the right variables to describe the supposed underlying geometric structure. Motivated by AdS/CFT considerations we investigate a supersymmetry breaking vacuum which is supposed to be the gravity dual to a metastable non-supersymmetric vacuum of a supersymmetric gauge theory. Supersymmetry is here broken by the addition of anti-branes; it is notoriously difficult to take into account their backreaction and we resort to use a perturbative technique. We compute the most general first order deformations of a D2-brane background, discuss the space of solutions of the deformed fields and argue about the nature of the unavoidable singularities which we encounter in the process
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De, Notariis Kevin. "Light hyperweak new gauge bosons from kinetic mixing in string models". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19491/.
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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.
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Kerstan, Max Bromo Buenaventura [Verfasser], i Arthur [Akademischer Betreuer] Hebecker. "Abelian gauge symmetries and fluxed instantons in compactifications of type IIB and F-theory / Max Bromo Buenaventura Kerstan ; Betreuer: Arthur Hebecker". Heidelberg : Universitätsbibliothek Heidelberg, 2013. http://d-nb.info/1177809389/34.
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Kerstan, Max [Verfasser], i Arthur [Akademischer Betreuer] Hebecker. "Abelian gauge symmetries and fluxed instantons in compactifications of type IIB and F-theory / Max Bromo Buenaventura Kerstan ; Betreuer: Arthur Hebecker". Heidelberg : Universitätsbibliothek Heidelberg, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:16-heidok-156687.
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Parsian, Mohammadhadi. "Supersymmetric Backgrounds in string theory". Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/97995.
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In the first part of this thesis, we investigate a way to find the complex structure moduli, for a given background of type IIB string theory in the presence of flux in special cases. We introduce a way to compute the complex structure and axion dilaton moduli explicitly. In the second part, we discuss $(0,2)$ supersymmetric versions of some recent exotic $mathcal{N}=(2,2)$ supersymmetric gauged linear sigma models, describing intersections of Grassmannians. In the next part, we consider mirror symmetry for certain gauge theories with gauge groups $F_4$, $E_6$, and $E_7$. In the last part of this thesis, we study whether certain branched-double-cover constructions in Landau-Ginzburg models can be extended to higher covers.Doctor of Philosophy
This thesis concerns string theory, a proposal for unification of general relativity and quantum field theory. In string theory, the building block of all the particles are strings, such that different vibrations of them generate particles. String theory predicts that spacetime is 10-dimensional. In string theorist's intuition, the extra six-dimensional internal space is so small that we haven't detected it yet. The physics that string theory predicts we should observe, is governed by the shape of this six-dimensional space called a `compactification manifold.' In particular, the possible ways in which this geometry can be deformed give rise to light degrees of freedom in the associated observable physical theory. In the first part of this thesis, we determine these degrees of freedom, called moduli, for a large class of solutions of the so-called type IIB string theory. In the second part, we focus on constructing such spaces explicitly. We also show that there can be different equivalent ways of constructing the same internal space. The third part of the thesis concerns mirror symmetry. Two compactification manifolds are called mirror to each other, when they both give the same four-dimensional effective theory. In this part, we describe the mirror of two-dimensional gauge theories with $F_4$, $E_6$, and $E_7$ gauge group, using the Gu-Sharpe proposal.
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Pajer, Enrico [Verfasser]. "Phenomenological aspects of type IIB flux compactifications / Enrico Pajer". 2008. http://d-nb.info/990295567/34.
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Cownden, Bradley. "Linear perturbations of type IIB SUGRA in flux compactifications". 2015. http://hdl.handle.net/1993/30168.
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We consider linear perturbations of the background type IIB SUGRA solutions and find the equations of motion for the moduli. In particular, we allow for spacetime fluctuations of the positions of D3-branes in the compact dimensions. We postulate an ansatz for the 5-form flux due to the motion of the D3-branes, and a corresponding first-order part of the metric. The movement of the D3-branes is then shown to affect the warp factor at linear order. Using the equations of motion for the D3-branes, the universal volume modulus, and the universal axion, we construct a second-order, effective action. Finally, based on the form of the effective action, we examine a Kahler potential for the moduli space.
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Ihl, Matthias 1977. "Topics in flux compactifications of type IIA superstring theory". 2008. http://hdl.handle.net/2152/7680.
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Realistic four-dimensional model building from string theory has been a focus of the string theory community ever since its inception. Toroidal orientifold constructions have emerged as a technically simple class of candidate models. Novel ingredients, such as background fluxes, have been discovered and intensely studied over the past few years. They allow for a (partial) solution of several long standing problems associated with model building in this framework. In this thesis, I summarize progress
that has been made in toroidal orientifold constructions in type IIA string theory.This includes a detailed discussion of moduli stabilization and (non-) supersymmetric AdS and Minkowski vacua. Furthermore I commence a systematic study of generalized NSNS, i.e., metric and non-geometric, fluxes. The emergence of novel D-terms is presented in detail. While most of the discussion applies to generic orientifolds of T⁶, most features are exemplified by and studied in terms of a certain orientifold of T⁶/ℤ₄ owing to its somewhat richer structure compared to simpler models studied before. It is also briefly reported on efforts of finding de Sitter vacua and inflation in this class of models.text
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Moster, Sebastian [Verfasser]. "Applications of the D-instanton calculus in type IIB orientifold compactifications / vorgelegt von Sebastian Moster". 2010. http://d-nb.info/1005059691/34.
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Körs, Simon [Verfasser]. "Type IIA flux compactifications : vacua, effective theories and cosmological challenges / vorgelegt von Simon Körs". 2009. http://d-nb.info/996530274/34.
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