Inflation in Gauged 6D Supergravity

In this note we demonstrate that chaotic inflation can naturally be realized in the context of an anomaly free minimal gauged supergravity in D=6 which has recently been the focus of some attention. This particular model has a unique maximally symmetric ground state solution, $R^{3,1} \times S^2$ which leaves half of the six-dimensional supersymmetries unbroken. In this model, the inflaton field $\phi$ originates from the complex scalar fields in the D=6 scalar hypermultiplet. The mass and the self couplings of the scalar field are dictated by the D=6 Lagrangian. The scalar potential has an absolute munimum at $\phi = 0$ with no undetermined moduli fields. Imposing a mild bound on the radius of $S^2$ enables us to obtain chaotic inflation. The low eenrgy equations of motion are shown to be consistent for the range of scalar field values relevant for inflation.Comment: one reference adde

Rapid Tunneling and Percolation in the Landscape

Motivated by the possibility of a string landscape, we reexamine tunneling of a scalar field across single/multiple barriers. Recent investigations have suggested modifications to the usual picture of false vacuum decay that lead to efficient and rapid tunneling in the landscape when certain conditions are met. This can be due to stringy effects (e.g. tunneling via the DBI action), or by effects arising due to the presence of multiple vacua (e.g. resonance tunneling). In this paper we discuss both DBI tunneling and resonance tunneling. We provide a QFT treatment of resonance tunneling using the Schr\"odinger functional approach. We also show how DBI tunneling for supercritical barriers can naturally lead to conditions suitable for resonance tunneling. We argue using basic ideas from percolation theory that tunneling can be rapid in a landscape where a typical vacuum has multiple decay channels and discuss various cosmological implications. This rapidity vacuum decay can happen even if there are no resonance/DBI tunneling enhancements, solely due to the presence of a large number of decay channels. Finally, we consider various ways of circumventing a recent no-go theorem for resonance tunneling in quantum field theory.Comment: 47 pages, 16 figures. Acknowledgements adde

A transformational treatment of Hindi verbal syntax.

After acknowledgments and a general index, the thesis opens with an introductory chapter which gives a brief outline of the theory and model of grammatical description upon which this study is based, and reviews the previous work on Hindi verbal syntax. This is followed by the two main chapters of the work. In chapter 2 Hindi sentence structure and the sub-classes of verb which are relevant for the for the fornulatioa of the Constituent Structure rules are discussed, before the rules thenselves are set out. Chapter 5 first gives some of the singuiary transformations, the nominalization, adjectivalization and adverbialization rules follow, and the chapter ends with the singulary transformational rules. The Appendix following these three chapters comprises a lexicon which lives a list of Hindi verbs with their appropriate syntactic, selectional and semantic features, and lists of the other lexical categories with only their selectional features. The thesis ends with a bibliography of works on general linguistic theory and the model of Transformational - Generative Crammar on the one hand, and on Hindi language on the other

Dynamical Dark Energy and Spontaneously Generated Gravity

We study the cosmological evolution of an induced gravity model with a scale symmetry breaking potential for the scalar field. The radiation to matter transition, following inflation and reheating, influences the dynamics of such a field through its non minimal coupling. We illustrate how, under certain conditions on the potential, such a dynamics can lead to a suitable amount of dark energy explaining the present accelerated expansion.Comment: 14 pages, 3 figure

Moduli Stabilization with Long Winding Strings

Stabilizing all of the modulus fields coming from compactifications of string theory on internal manifolds is one of the outstanding challenges for string cosmology. Here, in a simple example of toroidal compactification, we study the dynamics of the moduli fields corresponding to the size and shape of the torus along with the ambient flux and long strings winding both internal directions. It is known that a string gas containing states with non-vanishing winding and momentum number in one internal direction can stabilize the radius of this internal circle to be at self-dual radius. We show that a gas of long strings winding all internal directions can stabilize all moduli, except the dilaton which is stabilized by hand, in this simple example.Comment: title changed, improved presentation; reference added. 18 pages, JHEP styl

Orientifolds and Mirror Symmetry

We study parity symmetries and crosscap states in classes of N=2 supersymmetric quantum field theories in 1+1 dimensions, including non-linear sigma models, gauged WZW models, Landau-Ginzburg models, and linear sigma models. The parity anomaly and its cancellation play important roles in many of them. The case of the N=2 minimal model are studied in complete detail, from all three realizations -- gauged WZW model, abstract RCFT, and LG models. We also identify mirror pairs of orientifolds, extending the correspondence between symplectic geometry and algebraic geometry by including unorientable worldsheets. Through the analysis in various models and comparison in the overlapping regimes, we obtain a global picture of orientifolds and D-branes.Comment: 137 page

Flavor brane on the baryonic branch of moduli space

We study an extra flavor in the cascading SU((k+1)M)xSU(k M) gauge theory by adding probe D7-brane to the geometry. By finding a solution to the kappa-symmetry equation we establish that the D7-brane is mutually supersymmetric with the background everywhere on the baryonic branch of moduli space. We also discuss possible applications of this result.Comment: 15 pages; v2 typo corrected, references adde

Assessing a candidate IIA dual to metastable supersymmetry-breaking

We analyze the space of linearized non-supersymmetric deformations around a IIA solution found by Cvetic, Gibbons, Lu and Pope (CGLP) in hep-th/0101096. We impose boundary conditions aimed at singling out among those perturbations those describing the backreaction of anti-D2 branes on the CGLP background. The corresponding supergravity solution is a would-be dual to a metastable supersymmetry-breaking state. However, it turns out that this candidate bulk solution is inevitably riddled with IR divergences of its flux densities and action, whose physical meaning and implications for models of string cosmology call for further investigation.Comment: 33 pages. v2: reference added, clarifications in the introductio

Vacuum Energy Density and Cosmological Constant in dS Brane World

We discuss the vacuum energy density and the cosmological constant of dS$_5$ brane world with a dilaton field. It is shown that a stable AdS$_4$ brane can be constructed and gravity localization can be realized. An explicit relation between the dS bulk cosmological constant and the brane cosmological constant is obtained. The discrete mass spectrum of the massive scalar field in the AdS$_4$ brane is used to acquire the relationship between the brane cosmological constant and the vacuum energy density. The vacuum energy density in the brane gotten by this method is in agreement with astronomical observations.Comment: 16 pages,4 figure

T-duality, Fiber Bundles and Matrices

We extend the T-duality for gauge theory to that on curved space described as a nontrivial fiber bundle. We also present a new viewpoint concerning the consistent truncation and the T-duality for gauge theory and discuss the relation between the vacua on the total space and on the base space. As examples, we consider S^3(/Z_k), S^5(/Z_k) and the Heisenberg nilmanifold.Comment: 24 pages, typos correcte