New Vistas in Braneworld Cosmology

Traditionally, higher-dimensional cosmological models have sought to provide a description of the fundamental forces in terms of a unifying geometrical construction. In this essay we discuss how, in their present incarnation, higher-dimensional `braneworld' models might provide answers to a number of cosmological puzzles including the issue of dark energy and the nature of the big-bang singularity.Comment: Honorable mention in the 2002 Essay Competition of the Gravity Research Foundation. 10 pages, 2 figure

Quantum mechanical study of molecules transition probabilities, Einstein A coefficients and oscillator strengths of some band systems of diatomic molecules

Quantum mechanical study of transition probabilities, Einstein A coefficients, and oscillator strengths of band systems of diatomic molecule

Asymmetric embedding in brane cosmology

We derive a system of cosmological equations for a braneworld with induced curvature which is a junction between several bulk spaces. The permutation symmetry of the bulk spaces is not imposed, and the values of the fundamental constants, and even the signatures of the extra dimension, may be different on different sides of the brane. We then consider the usual partial case of two asymmetric bulk spaces and derive an exact closed system of scalar equations on the brane. We apply this result to the cosmological evolution on such a brane and describe its various partial cases.Comment: 10 page

Calculation System Computerized Royalty / Fee Author in CV. Ghalian Indonesia

Once the importance of the role of presenting the report royalties / fee author on the CV. Ghalia Indonesia, especially for the administration / administration because it can affect perpormance and improvement of the company. Activities of this author's presentation of the report i s still using the manual way, ie in terms of the counting process by the administrative fee, in addition, it needs a lot of places to store the lists of books and lists the security of transactions take a long time and other things. Seeing the lack of efficiency of the above activities, the problem also influences the effectiveness of future work, while the number of lists of books, branches and transactions continue to increase and require more rapid and precise information, it is worth noting and created a system computerize

APSIS - an Artificial Planetary System in Space to probe extra-dimensional gravity and MOND

A proposal is made to test Newton's inverse-square law using the perihelion shift of test masses (planets) in free fall within a spacecraft located at the Earth-Sun L2 point. Such an Artificial Planetary System In Space (APSIS) will operate in a drag-free environment with controlled experimental conditions and minimal interference from terrestrial sources of contamination. We demonstrate that such a space experiment can probe the presence of a "hidden" fifth dimension on the scale of a micron, if the perihelion shift of a "planet" can be measured to sub-arc-second accuracy. Some suggestions for spacecraft design are made.Comment: 17 pages, revtex, references added. To appear in Special issue of IJMP

Accelerating Universes with Scaling Dark Matter

Friedmann-Robertson-Walker universes with a presently large fraction of the energy density stored in an $X$-component with $w_X<-1/3$, are considered. We find all the critical points of the system for constant equations of state in that range. We consider further several background quantities that can distinguish the models with different $w_X$ values. Using a simple toy model with a varying equation of state, we show that even a large variation of $w_X$ at small redshifts is very difficult to observe with $d_L(z)$ measurements up to $z\sim 1$. Therefore, it will require accurate measurements in the range $1<z<2$ and independent accurate knowledge of $\Omega_{m,0}$ (and/or $\Omega_{X,0}$) in order to resolve a variable $w_X$ from a constant $w_X$.Comment: submitted to IJMPD (uses Latex, 12 pages, 6 Figures) Minor corrections, Figures 4, 6 revised. Conclusions unchange

Quantum effects, soft singularities and the fate of the universe in a braneworld cosmology

We examine a class of braneworld models in which the expanding universe encounters a "quiescent" future singularity. At a quiescent singularity, the energy density and pressure of the cosmic fluid as well as the Hubble parameter remain finite while all derivatives of the Hubble parameter diverge (i.e., ${\dot H}$, ${\ddot H}$, etc. $\to \infty$). Since the Kretschmann invariant diverges ($R_{iklm}R^{iklm} \to \infty$) at the singularity, one expects quantum effects to play an important role as the quiescent singularity is approached. We explore the effects of vacuum polarization due to massless conformally coupled fields near the singularity and show that these can either cause the universe to recollapse or, else, lead to a softer singularity at which $H$, ${\dot H}$, and ${\ddot H}$ remain finite while {\dddot H} and higher derivatives of the Hubble parameter diverge. An important aspect of the quiescent singularity is that it is encountered in regions of low density, which has obvious implications for a universe consisting of a cosmic web of high and low density regions -- superclusters and voids. In addition to vacuum polarization, the effects of quantum particle production of non-conformal fields are also likely to be important. A preliminary examination shows that intense particle production can lead to an accelerating universe whose Hubble parameter shows oscillations about a constant value.Comment: 19 pages, 3 figures, text slightly improved and references added. Accepted for publication in Classical and Quantum Gravit

Gravitational instability on the brane: the role of boundary conditions

An outstanding issue in braneworld theory concerns the setting up of proper boundary conditions for the brane-bulk system. Boundary conditions (BC's) employing regulatory branes or demanding that the bulk metric be nonsingular have yet to be implemented in full generality. In this paper, we take a different route and specify boundary conditions directly on the brane thereby arriving at a local and closed system of equations (on the brane). We consider a one-parameter family of boundary conditions involving the anisotropic stress of the projection of the bulk Weyl tensor on the brane and derive an exact system of equations describing scalar cosmological perturbations on a generic braneworld with induced gravity. Depending upon our choice of boundary conditions, perturbations on the brane either grow moderately (region of stability) or rapidly (instability). In the instability region, the evolution of perturbations usually depends upon the scale: small scale perturbations grow much more rapidly than those on larger scales. This instability is caused by a peculiar gravitational interaction between dark radiation and matter on the brane. Generalizing the boundary conditions obtained by Koyama and Maartens, we find for the Dvali-Gabadadze-Porrati model an instability, which leads to a dramatic scale-dependence of the evolution of density perturbations in matter and dark radiation. A different set of BC's, however, leads to a more moderate and scale-independent growth of perturbations. For the mimicry braneworld, which expands like LCDM, this class of BC's can lead to an earlier epoch of structure formation.Comment: 35 pages, 9 figures, an appendix and references added, version to be published in Classical and Quantum Gravit

Cosmological scalar fields that mimic the ΛCDM\Lambda CDM cosmological model

We look for cosmologies with a scalar field (dark energy without cosmological constant), which mimic the standard $\Lambda CDM$ cosmological model yielding exactly the same large-scale geometry described by the evolution of the Hubble parameter (i.e. photometric distance and angular diameter distance as functions on $z$). Asymptotic behavior of the field solutions is studied in the case of spatially flat Universe with pressureless matter and separable scalar field Lagrangians (power-law kinetic term + power-law potential). Exact analytic solutions are found in some special cases. A number of models have the field solutions with infinite behavior in the past or even singular behavior at finite redshifts. We point out that introduction of the cosmological scalar field involves some degeneracy leading to lower precision in determination of $\Omega_m$. To remove this degeneracy additional information is needed beyond the data on large-scale geometry.Comment: VIII International Conference "Relativistic Astrophysics, Gravitation and Cosmology": May 21-23, 2008, Kyiv, Ukrain