Space-like Dp branes: accelerating cosmologies versus conformally de Sitter space-time

We consider the space-like D$p$ brane solutions of type II string theories having isometries ISO$(p+1)$ $\times$ SO$(8-p,1)$. These are asymptotically flat solutions or in other words, the metrics become flat at the time scale $\tau \gg \tau_0$. On the other hand, when $\tau \sim \tau_0$, we get $(p+1)+1$ dimensional flat FLRWmetrics upon compactification on a $(8-p)$ dimensional hyperbolic space with time dependent radii. We show that the resultant $(p+1)+1$ dimensional metrics describe transient accelerating cosmologies for all $p$ from 1 to 6, i.e., from $(2+1)$ to $(7+1)$ space-time dimensions. We show how the acceleration changes with the interplay of the various parameters characterizing the solutions in $(3+1)$ dimensions. Finally, for $\tau \ll \tau_0$, after compactification on $(8-p)$ dimensional hyperbolic space, the resultant metrics are shown to take the form of $(p+1)+1$ dimensional de Sitter spaces upto a conformal transformation. Cosmologies here are decelerating, but, only in a particular conformal frame we get eternal acceleration.Comment: 18 pages, 7 figures; v2: major revision, accelerating cosmologies obtained for all $p$, paper has been corrected accordingly, figures improved; v3: typos fixed, minor changes and more clarifications added, version to appear in JHE

Decoupling limit and throat geometry of non-susy D3 brane

In a previous work, we have shown that, like BPS Dp branes, bulk gravity gets decoupled from the brane even for the non-susy Dp branes of type II string theories indicating a possible extension of AdS/CFT correspondence for the non-supersymmetric case. In that work, the decoupling of gravity on the non-susy Dp branes has been shown numerically for the general case as well as analytically for some special case. Here we discuss the decoupling limit and the throat geometry of the non-susy D3 brane when the charge associated with the brane is very large. We show that in the decoupling limit the throat geometry of the non-susy D3 brane, under appropriate coordinate change, reduces to the Constable-Myers solution and thus confirming that this solution is indeed the holographic dual of a (non-gravitational) gauge theory discussed there. We also show that when one of the parameters of the solution takes a specific value, it reduces, under another coordinate change, to the five-dimensional solution obtained by Csaki and Reece, again confirming its gauge theory interpretation.Comment: 5 pages, no figures; v2: two-column ReVTeX format, shortened with more clarifications and references, version to appear in Phys Lett

Wilson loop calculation in QGP using non-supersymmetric AdS/CFT

Previously, two of the present authors obtained the decoupling limit and the corresponding throat geometry of non-supersymmetric D3 brane solution of type IIB string theory. In analogy with the supersymmetric case, it describes the gravity dual of a non-supersymmetric gauge theory with QCD-like properties such as running coupling and confinement (or mass gap) in certain range of its parameters. In this paper, we consider a `black' version of the non-supersymmetric D3 brane solution in the decoupling limit and use this gravity background to holographically compute the expectation value of a time-like Wilson loop which, in turn, is related to the potential of a heavy quark-antiquark pair. By boosting the gravity solution along one of the brane directions and placing the pair at an arbitrary orientation with this direction, we numerically obtain the variation of the screening length as well as the potential with velocity, its orientation with respect to the direction of motion and other parameters of the theory. Remarkably enough, our results are in qualitative agreement with those obtained holographically in supersymmetric gauge theories indicating that these features are quite robust and universal as they are insensitive to the presence of any supersymmetry in the theory. The physical interpretations of the variations with respect to the other parameters of the theory, not observed in supersymmetric theory, have also been given.Comment: 21 pages, 10 figures; v2:some corrections made and a footnote added; v3: more clarifications and some references added, version to appear in Nucl. Phys.

Evaluation of Open Data Government Sites: A Comparative Study

The problems of open data government sites are mainly in the way data is presented by various government data repositories. There are no metadata standards, specifications, or protocols to achieve better discoverability and interoperability. This paper aims to find a way to solve the problems with open data government sites and propose a framework to provide web based data services which will be semantically structured and also propose a common metadata standard or mechanism for interoperability. Six data government sites have been selected for the study, according to the more number of dataset available and also to cover all continents of the world (followed convenience sampling logic). A framework has been suggested in this paper and it is expected that some government sites may follow the framework in the near future

Investigations of the Reactivity of Bis(trichlorostannyl)organyl Compounds

In the preceding work, some topics of organotin chalcogenide chemistry were added to this field regarding the following four aspects: i) the synthesis of new bis[tris(arylchalcogenolato)stannyl]organyls; ii) the potential physical and chemical applications of the newly synthesized bis[tris(arylchalcogenolate)stannyl]organyl compounds; iii) the reactivity of bis(trichlorostannyl)organyls or triorganotin chloride towards coinage metal complexes in the presence of PhSeSiMe3; and iv) the reactivity of bis(trichlorostannyl)organyls towards chalcogenide or/and transition metal complexes under solvothermal condition. This way, the work intended to a) explore whether arylchlcogenolato complexes of bis(trichlorostannyl)organyls are possible precursors for thermolysis for the synthesis of tin chalcogenide materials or serve as donor ligands for linkage of transition metal ions or for the formation of metal chalcogenolate complexes b) explore whether the reactivity of bis(trichlorostannyl)organyls toward chalcogenide or chalcogenolate and transition metals lead to the formation of organo-clad or organo-bridged complexes or clusters. Bis(trichlorostannyl)organyl compounds (Cl3Sn–R–SnCl3) were reacted with sodium thiophenolate in methanol or with 2-thionaphthol in toluene in the presence of triethylamine as a base to end up with the formation of bis[tris(arylthiolato)stannyl]organyls of the general type [(R,S)3Sn–R–Sn(SR,)3] (1-5). The selenium analogue of compounds 1-5 were synthesized by reaction of bis(trichlorostannyl)organyl compounds with diaryl diselenide in presence of a reducing agent (NaBH4) in ethanol. These reactions gave rise for the synthesis of compounds 6-11. In ensuing studies, the bis[tris(arylchalcogenolato)stannyl]organyl compounds prepared as discussed above were used as synthons for the synthesis of tin chalogenide materials or metal-arylchalcogenolato clusters. Thermolysis of (PhS)3Sn–Bu–Sn(SPh)3 and (PhSe)3Sn–Bu–Sn(SePh)3 lead to the formation of binary SnS2 and SnSe2 at 375 and 335 ºC. (PhSe)3Sn–Bu–Sn(SePh)3 was reacted with palladium acetate in dichloromethane to end up with a tetrameric complex of palladium and selenophenolate, [Pd(SePh)(OAc)]4 (12). Compound 12 possesses rectangular Pd4 arrangement.In order to explore the reactivity, bis(trichlorostannyl)organyl compounds were reacted with PhSeSiM3 and triphenyl phosphine complexes of coinage metals (Cu, Ag). The reaction of bis(trichlorostannyl)organyl with (PPh3)3AgNO3 a neutral tetradecanuclear silver cluster, [(Ph3PAg)8(SePh)12(μ6-Se)Ag6]•6THF (14) was obtained. In both cases, bis(trichlorostannyl)organyl compounds were not incorporated into the products. The reaction of triphenyltin chloride or tricyclohexyltin chloride instead of bis(trichlorostannyl)organyls with PhSeSiM3 and (PPh3)3AgNO3 resulted in an ionic silver selenide cluster, [(Ph3PAg)8(SePh)12(μ6-Se)0.5Ag6][Ph3SnCl2]•6THF (15) or [(Ph3PAg)8(SePh)12(μ6-Se)0.5Ag6][Cy3SnCl2] (16). Here, cationic Ag14Se12.5 cluster cores covered by an organic blanket. The pecularty of these latter compounds is the s.o.f. = 0.5 at the central µ6–Se ligand. Thus, half of the clusters in 15, 16 contain a central Se ligand, whereas the other half exhibits an empty cluster center. The structures of the statistically distributed neutral and +2 charged clusters in 15, 16 are averaged over the crystal. The potentially free site within the 14 silver atoms rationalize the highgrade of disorder of the cluster atoms and correlate with the facts that some coinage metal chalcogenide clusters are able to capture E2– ions. An according reaction of bis(trichlorostannyl)butane with elemental sulfur in ethylenediamine under solvothermal condition resulted in the formation of a polymeric compound [SnS2•en] (17). In order to compare the reactivity of the bis(trichlorostannyl)butane precursor with metallic tin, metallic tin and elemental sulfur were reacted under the indentical reaction condition as for the synthesis of compound 17. The latter ended up with the formation of a thiostannate salt, [enH]4[Sn2S6]•en (18). Methanothermal (solvothermal) reaction of bis(trichlorostannyl)butane with Na2S•9H2O and (PPh3)3CuCl finally led to the formation of an organyl-clad Sn/Cu/S cluster, [(Ph3PCu)6{cyclo-(CH2)4SnS2}6Cu4Sn] (19), combining three peculiarities at once: being (a) mixed-metallic, (b) mixed-valent, and (c) walnut-type with a metalloid core, a metal sulfide shell and an organic surface. DFT calculations rationalized the electronic situation and showed that the observed intramolecular cyclization of n-butyl groups at the Sn atoms is thermodynamically not favored. Hence, the formation should be driven mainly by the reductive sulfidic conditions that led to the observed formation of elemental sulfur and reduction of SnIVCl4 to SnIICl2