We discuss certain aspects of string field theory and its applications in exploring the land- scape of classical string theory vacua. We start by giving a brief overview of various tree-level string field theories, as well as of some relevant mathematical background. As a byproduct of our general discussion of observables, we present a new gauge-invariant quantity for the A∞ formulation of open superstring field theory. Putting particular emphasis on perturba- tive methods, we proceed to review in detail the construction of tree-level effective actions governing the dynamics of a certain subset of degrees of freedom. In light of recent devel- opments, we also discuss efficient methods for evaluating certain vertices of zero-momentum effective actions for open superstring and heterotic string field theories in the presence of a global N = 2 worldsheet superconformal symmetry. We show how to apply this perturbative approach to study dynamics of the D(−1)/D3 system (both with and without a B-field), while also discussing a number of more complicated Dp-brane configurations. At generic points in their moduli spaces, such bound states of Dp-branes clearly cannot be described in terms of simple Dirichlet or Neumann boundary conditions. The rest of this thesis is therefore devoted to developing analytic...

Studiens syfte är att undersöka vad stråkpedagoger har för attityd och syn på begreppet genrebredd samt hur detta kan relateras till undervisning på musik- och kulturskola. Studiens teoretiska ramverk utgörs av diskurspsykologi. För att undersöka detta har fokusgrupper använts som metod där stråkpedagoger inom musik- och kulturskolor har fått diskutera sina synsätt på genrebredd. Gruppsamtalen spelades in med både ljud och bild för att sedan transkriberas. Transkriptionerna analyserades med diskursanalys för att urskilja vilka tolkningsrepertoarer som framträder i samtalen. I resultatdelen beskrivs de olika tolkningsrepertoarerna som framträtt. Stråkpedagogerna ger utlopp för en variation av tolkningsrepertoarer som presenteras genom två huvudteman: Genrebredd som beroende av flera faktorer samt Genrebredd i undervisningen. Vissa av tolkningsrepertoarerna är kontrasterande mot varandra och vissa innefattar variationer inom dem själva. De mest förekommande synsätten hos lärarna är enligt resultatet, att genrebredd beror mycket på deras egen bakgrund, samt att genrebredd ses som ett verktyg för att möta eleven. Samtliga lärare ger dock uttryck för en tolkningsrepertoar där genrebredd ses som ett viktigt arbete. I diskussionen lyfts resultatets mest framträdande tolkningsrepertoarer för att diskuteras i relation med tidigare presenterad litteratur och forskning samt till det teoretiska perspektivet. / The purpose of this study is to examine string teachers’ attitudes and views towards the term genre width and how this could be related to string education in Swedish community school of music. The theoretical framework of the study is discourse psychology. To examine this, focus groups were used as method where string teachers within Swedish Community Schools of music has discussed their point of views on genre width. The conversations were recorded by video and audio to later be transcribed. The transcriptions were analyzed with discourse analysis to distinguish the various interpretative repertoires. The string teachers provide an outlet for a variety of interpretative repertoires, which is presented in two main themes: Genre as dependent of several factors and genre in teaching context. Some of the interpretative repertoires are contrasting to one another and some includes variations within themselves. The most occurring of the teachers’ views seems to be that to broadening the genre, are dependent on their own background, and that it is looked upon as a tool for meeting the student. All teachers express an interpretative repertoire where genre width, is looked upon as an important work. In the discussion, the most highlighted interpretative repertoires of the results are being related to previous research and presented literature and to the theoretical perspective.

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<p>In this work, we consider the addition of a single neutral massive vector boson to the Standard Model (SM). This boson, which we refer to as N⁰, induces dipolar transitions between electrons and muons. We obtain bounds on the strength of its coupling and its mass: from the scattering process e+e- to mu+mu-; from its contribution to muonium-antimuonium oscillations; and from its possible contribution to the rare muon decay mu- to e+e-e-. In particular, we examine the two cases where the mediator is both heavy and light compared with the scattering energies for, and place constraints on the relevant parameters based on their contributions to the cross section and the forward-backward asymmetry. For muonium-antimuonium oscillations, we consider only the case where the mediator is heavy compared to all other scales, reducing its effect to an effective contact interaction. Finally, we consider an SU(2) invariant theory from which the N⁰ interaction emerges, and find that flavour diagonal interactions also emerge, giving a tree-level path for the decay mu- to e+e-e-. We find that the heavy N⁰ is not strongly constrained by this contribution, while the light N⁰ is very strongly constrained by it. Very generally, we find that the heavy N⁰ is much less constrained than other lepton flavour violating processes, while the constraints on the light N0 vary in strength between processes.</p> / Master of Science (MSc)

<p>This thesis addresses two separate naturalness issues which generically come to bear on physical theories with large extra dimensions, and so a gravity scale much lower than the Planck scale. The first is related to the observed stability of the proton, wherein we determine the relevant constraints on an additional gauge boson which conserves baryon number. Although several such proposals have been previously considered, our analysis is distinctive in its interest in lighter gauge boson masses (which naturally arise in such models), and in its focus on the dependence of constraints due to kinetic mixing effects. The second is related to the main purpose of large extra dimensions---namely, to address the smallness of the observed vacuum energy---wherein we compute the leading-order quantum corrections to the four-dimensional (4D) vacuum energy resulting from loops of extra-dimensional fields. We compute the contributions from bulk scalars (spin 0), fermions (spin 1/2), and gauge fields (spin 1) in a flux-stabilized, spheroidal extra-dimensional geometry whose rugby-ball shape is due to two codimension-2 branes---one at each pole. (We also obtain the corresponding beta functions for both bulk and brane operators.) These results are then combined to obtain the net contribution from various multiplets in the context of a particular supersymmetric extra-dimensional model that has been shown to give a vanishing result for the 4D vacuum energy at the classical level. Surprisingly, we find that supersymmetry can be preserved dynamically at one loop in the case of identical branes, without arranging any particular relationship between the brane parameters. Perturbing away from the case of identical branes is shown to give a positive 1-loop contribution to the 4D vacuum energy whose size is set by the radius of the extra dimensions.</p> / Doctor of Philosophy (PhD)

Constraint programming (CP) is a technology in which a combinatorial problem is modeled declaratively as a conjunction of constraints, each of which captures some of the combinatorial substructure of the problem. Constraints are more than a modeling convenience: every constraint is partially implemented by an inference algorithm, called a propagator, that rules out some but not necessarily all infeasible candidate values of one or more unknowns in the scope of the constraint. Interleaving propagation with systematic search leads to a powerful and complete solution method, combining a high degree of re-usability with natural, high-level modeling. A propagator can be characterized as a sound approximation of a constraint on an abstraction of sets of candidate values; propagators that share an abstraction are similar in the strength of the inference they perform when identifying infeasible candidate values. In this thesis, we consider abstractions of sets of candidate values that may be described by an elegant mathematical formalism, the Galois connection. We develop a theoretical framework from the correspondence between Galois connections and propagators, unifying two disparate views of the abstraction-propagation connection, namely the oft-overlooked distinction between representational and computational over-approximations. Our framework yields compact definitions of propagator strength, even in complicated cases (i.e., involving several types, or unknowns with internal structure); it also yields a method for the principled derivation of propagators from constraint definitions. We apply this framework to the extension of an existing CP solver to constraints over strings, that is, words of finite length. We define, via a Galois connection, an over-approximation for bounded-length strings, and demonstrate two different methods for implementing this overapproximation in a CP solver. First we use the Galois connection to derive a bounded-length string representation as an aggregation of existing scalar types; propagators for this representation are obtained by manual derivation, or automated synthesis, or a combination. Then we implement a string variable type, motivating design choices with knowledge gained from the construction of the over-approximation. The resulting CP solver extension not only substantially eases modeling for combinatorial string problems, but also leads to substantial efficiency improvements over prior CP methods.

During the last decade text mining has become a widely used discipline utilizing statistical and machine learning methods. We present the tm package which provides a framework for text mining applications within R. We give a survey on text mining facilities in R and explain how typical application tasks can be carried out using our framework. We present techniques for count-based analysis methods, text clustering, text classiffication and string kernels. (authors' abstract)

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.

This thesis contributes with a number of topics to the subject of string compactifications, especially in the instance of the E₈ × E₈ heterotic string theory compactified on smooth Calabi-Yau threefolds. In the first half of the work, I discuss the Hodge plot associated with Calabi-Yau threefolds that are hypersurfaces in toric varieties. The intricate structure of this plot is explained by the existence of certain webs of elliptic-K3 fibrations, whose mirror images are also elliptic-K3 fibrations. Such manifolds arise from reflexive polytopes that can be cut into two parts along slices corresponding to the K3 fiber. Any two half-polytopes over a given slice can be combined into a reflexive polytope. This fact, together with a remarkable relation on the additivity of Hodge numbers, give to the Hodge plot the appearance of a fractal. Moving on, I discuss a different type of web of manifolds, by looking at smooth Z₃-quotients of Calabi-Yau three-folds realised as complete intersections in products of projective spaces. Non-simply connected Calabi-Yau three-folds provide an essential ingredient in heterotic string compactifications. Such manifolds are rare in the classical constructions, but they can be obtained as quotients of homotopically trivial Calabi-Yau three-folds by free actions of finite groups. Many of these quotients are connected by conifold transitions. In the second half of the work, I explore an algorithmic approach to constructing E₈ × E₈ heterotic compactifications using holomorphic and poly-stable sums of line bundles over complete intersection Calabi-Yau three-folds that admit freely acting discrete symmetries. Such Abelian bundles lead to N = 1 supersymmetric GUT theories with gauge group SU(5) × U(4) and matter fields in the 10, ⁻10, ⁻5, 5 and 1 representations of SU(5). The extra U(1) symmetries are generically Green-Schwarz anomalous and, as such, they survive in the low energy theory only as global symmetries. These, in turn, constrain the low energy theory and in many cases forbid the existence of undesired operators, such as dimension four or five proton decay operators. The line bundle construction allows for a systematic computer search resulting in a plethora of models with the exact matter spectrum of the Minimally Supersymmetric Standard Model, one or more pairs of Higgs doublets and no exotic fields charged under the Standard Model group. In the last part of the thesis I focus on the case study of a Calabi-Yau hypersurface embedded in a product of four CP1 spaces, referred to as the tetraquadric manifold. I address the question of the finiteness of the class of consistent and physically viable line bundle models constructed on this manifold. Line bundle sums are part of a moduli space of non-Abelian bundles and they provide an accessible window into this moduli space. I explore the moduli space of heterotic compactifications on the tetraquadric hypersurface around a locus where the vector bundle splits as a direct sum of line bundles, using the monad construction. The monad construction provides a description of poly-stable S(U(4) × U(1))–bundles leading to GUT models with the correct field content in order to induce standard-like models. These deformations represent a class of consistent non-Abelian models that has co-dimension one in Kähler moduli space.

This thesis reviews the method of Mafra, Schlotterer, and Stieberger (2011) for computing the full colour ordered N-point open superstring amplitude using the Pure Spinor formalism. We introduce relevant elements of super Yang-Mills theory and examine the basics of the Pure Spinor formalism, with a focus on tools for amplitude computation. We then define a series of objects with increasingly useful BRST transformation properties, which greatly simplify the calculations, and show how these properties can be determined using a diagrammatic method. Finally, we use the explicit four- and five-point amplitude computations as stepping stones to compute the general N-point amplitude, which factors into a set of kinematic integrals multiplying SYM subamplitudes.