Plane symmetric viscous fluid cosmological models of the universe with a variable cosmological term are investigated. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density, whereas the coefficient of shear viscosity is taken as a constant. To get the deterministic solutions of the Einstein’s field equations, the free gravitational field is assumed to be of type D which is of the next order in the hierarchy of Petrov classification. The cosmological constant � is found to be a decreasing function of time and positive which is corroborated by the results from recent supernovae Ia observations. The physical and geometric aspects of the models are discussed.
I give a brief overview of the exploration of baryon properties in meson photo- and electroproduction. These processes provide ample information for the study of electromagnetic couplings of baryon resonances and to search for states, yet to be discovered. The CLAS detector, combined with the use of energy-tagged polarized photons and polarized electrons, as well as polarized targets and the measurement of recoil polarization, provide the tools for a comprehensive nucleon resonance program. I briefly present the status of this program, prospects for the next few years, and plans for the Jefferson Lab 12 GeV upgrade.
We present our results for the exclusive electroproduction of pions off nucleons and nuclei at high values of $Q^2$. In electroproduction of nuclei $A(e,e'\pi)$ we consider the Color Transparency (CT) effect recently observed at JLAB. It is shown that the description of $\pi$ production off nucleons is mandatory for the proof of the CT signal at JLAB. We further develop the models for exclusive production of $\pi$ off nucleons at JLAB and HERMES. At first we describe a model based on exclusive-inclusive connection. In the second approach we combine a Regge pole approach with the residual effect of nucleon resonances. The nucleon resonances are described using a dual connection between the exclusive form factors and inclusive deep inelastic structure functions. We present the results for the beam spin azimuthal asymmetries measured at JLAB in exclusive electroproduction of charged and neutral pions.
COMPASS is a fixed-target experiment at the CERN SPS for the investigation of the structure and the dynamics of hadrons. The experimental setup features a large acceptance and high momentum resolution spectrometer including particle identification and calorimetry and is therefore ideal to access a broad range of different final states. Following the promising observation of a spin-exotic resonance during an earlier pilot run, COMPASS focused on light-quark hadron spectroscopy during the years 2008 and 2009. A data set, world leading in terms of statistics and resolution, has been collected with a 190GeV/c hadron beam impinging on either liquid hydrogen or nuclear targets. Spin-exotic meson and glueball candidates formed in both diffractive dissociation and central production are presently studied. Since the beam composition includes protons, the excited baryon spectrum is also accessible. Furthermore, Primakoff reactions have the potential to determine radiative widths of the resonances and to probe chiral perturbation theory. An overview of the ongoing analyses will be presented. In particular, the employed partial wave analysis techniques will be illustrated and recent results will be shown for a selection of final states.
