Effect of annealing temperatures on TiO2 thin films prepared by spray pyrolysis deposition method

Titanium dioxide (TiO2) nanoparticles thin film has been successfully synthesized by a spray pyrolysis deposition method by using an air compressor on a fluorine-doped tin oxide (FTO) substrate and was annealed at different temperature. TiO2 is the most common oxide as an electrode in dye sensitized solar cell (DSSC) which still has chances of improvements to increase its efficiency as an electrode. The efficiency of a DSSC was relatively low but modifications on every part of a DSSC were currently in research progress and an increase in adsorbed dye molecules was considered a potential. Thus, the influences of annealing temperature on structural and morphological properties of TiO2 have been studied using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively, while the efficiency of the films in a solar cell was studied by a solar simulator. The FESEM result showed several degrees of porosity obtained by varying the annealing temperature. The crystallinity of TiO2 investigated by XRD showed that the crystallinity of the TiO2 thin films was generally unaffected by the annealing temperature. The relationship between the properties and the efficiency of the films as an electrode was also studied

The Volume of the Universe after Inflation and de Sitter Entropy

We calculate the probability distribution for the volume of the Universe after slow-roll inflation both in the eternal and in the non-eternal regime. Far from the eternal regime the probability distribution for the number of e-foldings, defined as one third of the logarithm of the volume, is sharply peaked around the number of e-foldings of the classical inflaton trajectory. At the transition to the eternal regime this probability is still peaked (with the width of order one e-folding) around the average, which gets twice larger at the transition point. As one enters the eternal regime the probability for the volume to be finite rapidly becomes exponentially small. In addition to developing techniques to study eternal inflation, our results allow us to establish the quantum generalization of a recently proposed bound on the number of e-foldings in the non-eternal regime: the probability for slow-roll inflation to produce a finite volume larger than e^(S_dS/2), where S_dS is the de Sitter entropy at the end of the inflationary stage, is smaller than the uncertainty due to non-perturbative quantum gravity effects. The existence of such a bound provides a consistency check for the idea of de Sitter complementarity.Comment: 47 pages, 11 figure

Effective theory for wall-antiwall system

We propose a useful method for deriving the effective theory for a system where BPS and anti-BPS domain walls coexist. Our method respects an approximately preserved SUSY near each wall. Due to the finite width of the walls, SUSY breaking terms arise at tree-level, which are exponentially suppressed. A practical approximation using the BPS wall solutions is also discussed. We show that a tachyonic mode appears in the matter sector if the corresponding mode function has a broader profile than the wall width.Comment: LaTeX file, 30 page, 5 eps figures, references adde

Passing through the bounce in the ekpyrotic models

By considering a simplified but exact model for realizing the ekpyrotic scenario, we clarify various assumptions that have been used in the literature. In particular, we discuss the new ekpyrotic prescription for passing the perturbations through the singularity which we show to provide a spectrum depending on a non physical normalization function. We also show that this prescription does not reproduce the exact result for a sharp transition. Then, more generally, we demonstrate that, in the only case where a bounce can be obtained in Einstein General Relativity without facing singularities and/or violation of the standard energy conditions, the bounce cannot be made arbitrarily short. This contrasts with the standard (inflationary) situation where the transition between two eras with different values of the equation of state can be considered as instantaneous. We then argue that the usually conserved quantities are not constant on a typical bounce time scale. Finally, we also examine the case of a test scalar field (or gravitational waves) where similar results are obtained. We conclude that the full dynamical equations of the underlying theory should be solved in a non singular case before any conclusion can be drawn.Comment: 17 pages, ReVTeX 4, 13 figures, minor corrections, conclusions unchange

The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang

We propose a cosmological scenario in which the hot big bang universe is produced by the collision of a brane in the bulk space with a bounding orbifold plane, beginning from an otherwise cold, vacuous, static universe. The model addresses the cosmological horizon, flatness and monopole problems and generates a nearly scale-invariant spectrum of density perturbations without invoking superluminal expansion (inflation). The scenario relies, instead, on physical phenomena that arise naturally in theories based on extra dimensions and branes. As an example, we present our scenario predominantly within the context of heterotic M-theory. A prediction that distinguishes this scenario from standard inflationary cosmology is a strongly blue gravitational wave spectrum, which has consequences for microwave background polarization experiments and gravitational wave detectors.Comment: 67 pages, 4 figures. v2,v3: minor corrections, references adde

Particle physics models of inflation

Inflation models are compared with observation on the assumption that the curvature perturbation is generated from the vacuum fluctuation of the inflaton field. The focus is on single-field models with canonical kinetic terms, classified as small- medium- and large-field according to the variation of the inflaton field while cosmological scales leave the horizon. Small-field models are constructed according to the usual paradigm for beyond Standard Model physicsComment: Based on a talk given at the 22nd IAP Colloquium, ``Inflation +25'', Paris, June 2006 Curve omitted from final Figur

Variable-Speed-of-Light Cosmology from Brane World Scenario

We argue that the four-dimensional universe on the TeV brane of the Randall-Sundrum scenario takes the bimetric structure of Clayton and Moffat, with gravitons traveling faster than photons instead, while the radion varies with time. We show that such brane world bimetric model can thereby solve the flatness and the cosmological constant problems, provided the speed of a graviton decreases to the present day value rapidly enough. The resolution of other cosmological problems such as the horizon problem and the monopole problem requires supplementation by inflation, which may be achieved by the radion field provided the radion potential satisfies the slow-roll approximation.Comment: 18 pages, LaTeX, revised version to appear in Phys. Rev.

Supersymmetry and Superstring Phenomenology

We briefly cover the early history of supersymmetry, describe the relation of SUSY quantum field theories to superstring theories and explain why they are considered a likely tool to describe the phenomenology of high energy particle theory beyond the Standard Model.Comment: 18 pages. To be published in ``Supersymmetry on the Eve of the LHC'', a special volume of the European Physical Journal C (EPJC) dedicated to the memory of Julius Wes

Solvable Models of Domain Walls in N=1 Supergravity

A class of exactly solvable models of domain walls are worked out in D=4 ${\cal N}=1$ supergravity. We develop a method to embed globally supersymmetric theories with exact BPS domain wall solutions into supergravity, by introducing a gravitationally deformed superpotential. The gravitational deformation is natural in the spirit of maintaining the K\"ahler invariance. The solutions of the warp factor and the Killing spinor are also obtained. We find that three distinct behaviors of warp factors arise depending on the value of a constant term in the superpotential : exponentially decreasing in both sides of the wall, flat in one side and decreasing in the other, and increasing in one side and decreasing in the other. Only the first possibility gives the localized massless graviton zero mode. Models with multi-walls and models with runaway vacua are also discussed.Comment: 10 pages, 3 figures; Misprints in three formulas are correcte

A Pure-Glue Hidden Valley I. States and Decays

It is possible that the standard model is coupled, through new massive charged or colored particles, to a hidden sector whose low energy dynamics is controlled by a pure Yang-Mills theory, with no light matter. Such a sector would have numerous metastable "hidden glueballs" built from the hidden gluons. These states would decay to particles of the standard model. We consider the phenomenology of this scenario, and find formulas for the lifetimes and branching ratios of the most important of these states. The dominant decays are to two standard model gauge bosons, or by radiative decays with photon emission, leading to jet- and photon-rich signals.Comment: 34 pages, 4 figure