Electronic Structure of Ordered Double Perovskite Ba2CoWO6

Ba2CoWO6 (BCoW) has been synthesized in polycrystalline form by solid state reaction at 1200C. Structural characterization of the compound was done through X-ray diffraction (XRD) followed by Rietveld analysis of the XRD pattern. The crystal structure is cubic, space group Fm-3m (No 225) with the lattice parameter, a=8.210A. Optical band-gap of the present system has been calculated using the UV-Vis Spectroscopy and Kubelka-Munk function, its value being 2.45 eV. A detailed study of the electronic properties has also been carried out using the density functional theory (DFT) techniques implemented on WIEN2k. Importance of electron-electron interaction between the Co ions leading to half-metallic behavior, crystal and exchange splitting together with the hybridization between O and Co, W has been investigated using the total and partial density of states.

Feebly Self-Interacting Cold Dark Matter: New theory for the Core-Halo structure in GLSB Galaxies

We explore the low energy cosmological dynamics of feebly self-interacting cold dark matter and propose a new simple explanation for the rotation curves of the core-halo model in massive LSB (Low Surface brightness)galaxies. We argue in favor of the truly collisionless nature of cold dark matter,which is feebly,self-interacting at small scales between epochs of equality and recombination.For this, we assume a model, wherein strongly coupled baryon-radiation plasma ejects out of small regions of concentrated cold dark matter without losing its equilibrium. We use the Merscerskii equation i.e. the variable mass formalism of classical dynamics.We obtain new results relating the oscillations in the CMB anisotropy to the ejection velocity of the baryon-radiation plasma,which can be useful tool for numerical work for exploring the second peak of CMB. Based on this model, we discuss the growth of perturbations in such a feebly self-interacting,cold dark matter both in the Jeans theory and in the expanding universe using Newtons theory.We obtain an expression for the growth of fractional perturbations in cold dark matter,which reduce to the standard result of perturbation theory for late recombination epochs. We see the effect of the average of the perturbations in the cold dark matter potential on the cosmic microwave background temperature anisotropy that originated at redshifts between equality and recombination i.e. 1100 < z < z_{eq}. Also we obtain an expression for the Sachs-Wolfe effect,i.e. the CMB temperature anisotropy at decoupling in terms of the average of the perturbations in cold dark matter potential.

Surface tension with Normal Curvature in Curved Space-Time

With an aim to include the contribution of surface tension in the action of the boundary, we define the tangential pressure in terms of surface tension and Normal curvature in a more naturally geometric way. First, we show that the negative tangential pressure is independent of the four-velocity of a very thin hyper-surface. Second, we relate the 3-pressure of a surface layer to the normal curvature and the surface tension. Third, we relate the surface tension to the energy of the surface layer. Four, we show that the delta like energy flows across the hyper-surface will be zero for such a representation of intrinsic 3-pressure. Five, for the weak field approximation and for static spherically symmetric configuration, we deduce the classical Kelvins relation. Six, we write a modified action for the boundary having contributions both from surface tension and normal curvature of the surface layer. Also we propose a method to find the physical action assuming a reference background, where the background is not flat.