115460279
Vestiges of the interaction between dark energy and dark matter
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 interaction between dark energy and dark matter.
118198563
Dark Energy: Relating the Evolutions of the Universe from the Past to the Future
Using the evolution history of the universe, one can make constraint on the parameter space of dynamic dark energy models. We discuss two different parameterized dark energy models. Our results further restrict the combined constraints obtained from supernova and the first-year Wilkinson-microwave-anisotropy-probe observations. From the allowed parameter space, it is found that our universe will experience an eternal acceleration. We also estimate the bound on the physically relevant regions both in the re-inflationary and inflationary phases.
124897627
Different Quantum Entropies for Two Kinds of Extreme Two-Dimensional Lowe–Strominger Black Holes*
It is shown that both the classical entropy of two-dimensional extremal Lowe–Strominger black hole and the quantum entropy of the scalar field in the background of this black hole are different by using Hawking's treatment as wel as Zaslavskii's treatment respectively. This result supports our previous suggestion that there are two kinds of extreme black holes in the nature. A new divergent term emerges in the quantum entropy in Zaslavskii's treatment and its physical meaning has been discussed.
30079794
Stability of the event horizon in (2+1)-dimensional black holes.
118997018
Probing the curvature of the Universe from supernova measurement
We study the possibility to probe the spatial geometry of the Universe by supernova measurement. We illustrate with an accelerating universe model with infinite-volume extra dimensions, for which the 1σ level supernova results indicate that the Universe is closed.
119186601
Various types of phase transitions in the AdS soliton background
We study the basic holographic insulator and superconductor phase transition in the AdS soliton background by generalizing the spontaneous breaking of a global U(1) symmetry to occur via Stuckelberg mechanism. We construct the soliton solutions with backreaction and examine the effects of the backreaction on the condensation of the scalar hair in the generalized Stuckelberg Lagrangian. We disclose rich physics in various phase transitions. In addition to the AdS soliton configuration, we also examine the property of the phase transition in the AdS black hole background.
119450767
Gas at Large Distances from Galaxies and QSO Absorption Lines
We present the calculations of steady, spherical gas outflows from galaxies in an effort to understand the effects of the galaxy mass on the flow properties such as the size of the outflow regions, the efficiency of radiative cooling, and the fate of the cooled gas. We show that there exist no transonic flows but either subsonic or supersonic flows are obtainable, in an analogy with the stellar wind or accretion problems. Solutions of the supersonic outflows are studied in detail as they are most likely to carry gas to large distances away from galaxies. In case the gas does cool radiatively, the cooled gas is most likely to form clouds via various instabilities. The clouds coast farther away from the galaxy because of the finite kinetic energy they inherit. Depending on the initial energies, the clouds can either leave the galaxy or fall back ballistically. Applications of the calculations to dwarf and normal galaxies are made, and we argue that normal galaxies like our own should have relatively small gaseous halos formed through this mechanism. We discuss the implications of cold clouds from dwarf galaxies on recent observations of the QSO absorption line systems. For massive galaxies, satellites provide alternative ways to form large gaseous halos. We show how dynamical friction can increase tidal stripping of the gas as the satellite spirals in toward the primary, and that the gas ejected from satellites may account for the QSO heavy element absorption lines.
121071019
OBSERVATIONAL H(z) DATA AS A COMPLEMENTARITY TO OTHER COSMOLOGICAL PROBES
In this paper, we use a set of observational H(z) data (OHD) to constrain the Lambda CDM cosmology. This dataset can be derived from the differential ages of the passively evolving galaxies. Meanwhile, the A-parameter, which describes the Baryonic Acoustic Oscillation (BAO) peak, and the newly measured value of the Cosmic Microwave Background (CMB) shift parameter Rare used to present combinational constraints on the same cosmology. The combinational constraints favor an accelerating flat universe while the flat Lambda CDM cosmology is also analyzed in the same way. We obtain result compatible with that by many other independent cosmological observations. We find that the observational H(z) data set is a complementarity to other cosmological probes.
119197867
Constraints on smoothness parameter and dark energy using observational H(z) data
With large-scale homogeneity, the universe is locally inhomogeneous, clustering into stars, galaxies and larger structures. Such property is described by the smoothness parameter α which is defined as the proportion of matter in the form of intergalactic medium. If we consider the inhomogeneities over a small scale, there should be modifications of the cosmological distances compared to a homogenous model. Dyer and Roeder developed a second-order ordinary differential equation (D-R equation) that describes the angular diameter distance-redshift relation for inhomogeneous cosmological models. Furthermore, we may obtain the D-R equation for observational H(z) data (OHD). The density-parameter ΩM, the state of dark energy ω, and the smoothness-parameter α are constrained by a set of OHD in a spatially flat ΛCDM universe as well as a spatially flat XCDM universe. By using a χ2 minimization method, we get α = 0.81+0.19−0.20 and ΩM = 0.32+0.12−0.06 at the 1σ confidence level. If we assume a Gaussian prior of ΩM = 0.26 ± 0.1, we get α = 0.93+0.07−0.19 and ΩM = 0.31+0.06−0.05. For the XCDM model, α is constrained to α ≥ 0.80 but ω is weakly constrained around −1, where ω describes the equation of state of the dark energy (pX = ωρX). We conclude that OHD constrains the smoothness parameter more effectively than the data of SNe Ia and compact radio sources.
121908282
QSO heavy-element absorption line systems and large galactic halos by satellite accretion
Recent observations indicate that the QSO heavy-element absorption line (HEAL) systems are associated with extremely large galactic halos. The origin of the absorbing gas, however, is not well understood. We demonstrate that an extremely large star formation rate is required if the HEAL gas originates from galactic disks. This is clearly incompatible with the observed moderate evolution and the normal colors of the galaxies associated with the Mg II absorption lines (MgALs). Studies of the H I high-velocity clouds, the Magellanic Stream, and recent observations of nearby QSOs suggest that the gas tidally torn out from the LMC/SMC system may be responsible for the MgALs observed in the Galactic halo
121864290
A compact positron annihilation lifetime spectrometer
Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size gamma-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the coincidence counting rate similar to 8 cps/mu Ci were achieved. A lifetime value of 219 +/- 1 ps of positron annihilation in well annealed Si was tested, which is in agreement with the typical values published in the previous lectures.