830 research outputs found
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, which leaves
half of the six-dimensional supersymmetries unbroken. In this model, the
inflaton field 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
with no undetermined moduli fields. Imposing a mild bound on the
radius of 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
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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
brane world with a dilaton field. It is shown that a stable AdS 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 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
Nanosecond image processing using stimulated photon echoes
Processing of two-dimensional images on a nanosecond time scale is demonstrated using the stimulated photon echoes in a rare-earth-doped crystal (0.1 at. \% Pr3:LaF3). Two spatially encoded laser pulses (pictures) resonant with the 3P0-3H4 transition of Pr3 were stored by focusing the image pulses sequentially into the Pr3:LaF3 crystal. The stored information is retrieved and processed by a third read pulse, generating the echo that is the spatial convolution or correlation of the input images. Application of this scheme to high-speed pattern recognition is discussed
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