The Holographic Model of Dark Energy and Thermodynamics of Non-Flat Accelerated Expanding Universe

Motivated by recent results on non-vanishing spatial curvature \cite{curve} we employ the holographic model of dark energy to investigate the validity of first and second laws of thermodynamics in non-flat (closed) universe enclosed by apparent horizon $R_A$ and the event horizon measured from the sphere of horizon named $L$. We show that for the apparent horizon the first law is roughly respected for different epochs while the second laws of thermodynamics is respected while for $L$ as the system's IR cut-off first law is broken down and second law is respected for special range of deceleration parameter. It is also shown that at late-time universe $L$ is equal to $R_A$ and the thermodynamic laws are hold, when the universe has non-vanishing curvature. Defining the fluid temperature to be proportional to horizon temperature the range for coefficient of proportionality is obtained provided that the generalized second law of thermodynamics is hold.Comment: 12 pages, no figure, abstract and text extended, references added, accepted for publication in JCA

Interacting holographic dark energy model and generalized second law of thermodynamics in non-flat universe

In the present paper we consider the interacting holographic model of dark energy to investigate the validity of the generalized second laws of thermodynamics in non-flat (closed) universe enclosed by the event horizon measured from the sphere of the horizon named $L$. We show that for $L$ as the system's IR cut-off the generalized second law is respected for the special range of the deceleration parameter.Comment: 11 pages, no figure

Super-acceleration on the Brane by Energy Flow from the Bulk

We consider a brane cosmological model with energy exchange between brane and bulk. Parameterizing the energy exchange term by the scale factor and Hubble parameter, we are able to exactly solve the modified Friedmann equation on the brane. In this model, the equation of state for the effective dark energy has a transition behavior changing from $w_{de}^{eff}>-1$ to $w_{de}^{eff}<-1$, while the equation of state for the dark energy on the brane has $w>-1$. Fitting data from type Ia supernova, Sloan Digital Sky Survey and Wilkinson Microwave Anisotropy Probe, our universe is predicted now in the state of super-acceleration with $w_{de0}^{eff}=-1.21$.Comment: Revtex, 11 pages including 2 figures,v2: tpos fixed, references added, to appear in JCA

The Holographic Dark Energy in a Non-flat Universe

We study the model for holographic dark energy in a spatially closed universe, generalizing the proposal in hep-th/0403127 for a flat universe. We provide independent arguments for the choice of the parameter $c=1$ in the holographic dark energy model. On the one hand, $c$ can not be less than 1, to avoid violating the second law of thermodynamics. On the other hand, observation suggests $c$ be very close to 1, it is hard to justify a small deviation of $c$ from 1, if $c>1$.Comment: 12 pages, harvmac, v2: order of authors is corrected in webpage, v3: refs. adde

Reconstructing the properties of dark energy from recent observations

We explore the properties of dark energy from recent observational data, including the Gold Sne Ia, the baryonic acoustic oscillation peak from SDSS, the CMB shift parameter from WMAP3, the X-ray gas mass fraction in cluster and the Hubble parameter versus redshift. The $\Lambda CDM$ model with curvature and two parameterized dark energy models are studied. For the $\Lambda CDM$ model, we find that the flat universe is consistent with observations at the $1\sigma$ confidence level and a closed universe is slightly favored by these data. For two parameterized dark energy models, with the prior given on the present matter density, $\Omega_{m0}$, with $\Omega_{m0}=0.24$, $\Omega_{m0}=0.28$ and $\Omega_{m0}=0.32$, our result seems to suggest that the trend of $\Omega_{m0}$ dependence for an evolving dark energy from a combination of the observational data sets is model-dependent.Comment: 16 pages, 15 figures, To appear in JCA

Fisher Matrix Preloaded -- Fisher4Cast

The Fisher Matrix is the backbone of modern cosmological forecasting. We describe the Fisher4Cast software: a general-purpose, easy-to-use, Fisher Matrix framework. It is open source, rigorously designed and tested and includes a Graphical User Interface (GUI) with automated LATEX file creation capability and point-and-click Fisher ellipse generation. Fisher4Cast was designed for ease of extension and, although written in Matlab, is easily portable to open-source alternatives such as Octave and Scilab. Here we use Fisher4Cast to present new 3-D and 4-D visualisations of the forecasting landscape and to investigate the effects of growth and curvature on future cosmological surveys. Early releases have been available at http://www.cosmology.org.za since May 2008 with 750 downloads in the first year. Version 2.2 is made public with this paper and includes a Quick Start guide and the code used to produce the figures in this paper, in the hope that it will be useful to the cosmology and wider scientific communities.Comment: 30 Pages, 15 figures. Minor revisions to match published version, with some additional functionality described to match the current version (2.2) of the code. Software available at http://www.cosmology.org.za. Usage, structure and flow of the software, as well as tests performed are described in the accompanying Users' Manua

Effects of the interaction between dark energy and dark matter on cosmological parameters

We examine the effects of possible phenomenological interactions between dark energy and dark matter on cosmological parameters and their efficiency in solving the coincidence problem. We work with two simple parameterizations of the dynamical dark energy equation of state and the constant dark energy equation of state. Using observational data coming from the new 182 Gold type Ia supernova samples, the shift parameter of the Cosmic Microwave Background given by the three-year Wilkinson Microwave Anisotropy Probe observations, and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, we perform a statistical joint analysis of different forms of phenomenological interactions between dark energy and dark matter.Comment: revised version, accepted for publication in JCA

Notes on interacting holographic dark energy model in a closed universe

We consider interacting holographic dark energy model in Friedmann Robertson Walker space time with positive spatial curvature and investigate the behavior of curvature parameter and dark energy density in accelerated expanding epoch. We also derive some conditions needed to cross the phantom divide line in this model.Comment: 10 pages, typos corrected, some explanations and references added and updated, accepted for publication in JCA

Gauss-Bonnet Cosmology with Induced Gravity and Non-Minimally Coupled Scalar Field on the Brane

We construct a cosmological model with non-minimally coupled scalar field on the brane, where Gauss-Bonnet and Induced Gravity effects are taken into account. This model has 5D character at both high and low energy limits but reduces to 4D gravity in intermediate scales. While induced gravity is a manifestation of the IR limit of the model, Gauss-Bonnet term and non-minimal coupling of scalar field and induced gravity are essentially related to UV limit of the scenario. We study cosmological implications of this scenario focusing on the late-time behavior of the solutions. In this setup, non-minimal coupling plays the role of an additional fine-tuning parameter that controls the initial density of predicted finite density big bang. Also, non-minimal coupling has important implication on the bouncing nature of the solutions.Comment: 33 pages, 12 figures, one table, revised and final version accepted for publication in JCA

Persistent Expression of Hepatitis C Virus Non-Structural Proteins Leads to Increased Autophagy and Mitochondrial Injury in Human Hepatoma Cells

HCV infection is a major cause of chronic liver disease and liver cancer in the United States. To address the pathogenesis caused by HCV infection, recent studies have focused on the direct cytopathic effects of individual HCV proteins, with the objective of identifying their specific roles in the overall pathogenesis. However, this approach precludes examination of the possible interactions between different HCV proteins and organelles. To obtain a better understanding of the various cytopathic effects of and cellular responses to HCV proteins, we used human hepatoma cells constitutively replicating HCV RNA encoding either the full-length polyprotein or the non-structural proteins, or cells constitutively expressing the structural protein core, to model the state of persistent HCV infection and examined the combination of various HCV proteins in cellular pathogenesis. Increased reactive oxygen species (ROS) generation in the mitochondria, mitochondrial injury and degeneration, and increased lipid accumulation were common among all HCV protein-expressing cells regardless of whether they expressed the structural or non-structural proteins. Expression of the non-structural proteins also led to increased oxidative stress in the cytosol, membrane blebbing in the endoplasmic reticulum, and accumulation of autophagocytic vacuoles. Alterations of cellular redox state, on the other hand, significantly changed the level of autophagy, suggesting a direct link between oxidative stress and HCV-mediated activation of autophagy. With the wide-spread cytopathic effects, cells with the full-length HCV polyprotein showed a modest antioxidant response and exhibited a significant increase in population doubling time and a concomitant decrease in cyclin D1. In contrast, cells expressing the non-structural proteins were able to launch a vigorous antioxidant response with up-regulation of antioxidant enzymes. The population doubling time and cyclin D1 level were also comparable to that of control cells. Finally, the cytopathic effects of core protein appeared to focus on the mitochondria without remarkable disturbances in the cytosol