18067084
Statistics of Weak Gravitational Lensing in Cold Dark Matter Models: Magnification Bias on Quasar Luminosity Functions
We compute statistical properties of weak gravitational lensing by large-scale structure in three cold dark matter (CDM) models: two —at models with 0) and (0.3, 0.7) and one open model () 0 , j 0 ) \ (1, with 0), where and are the density parameter and cosmological constant, respec- () 0 , j 0 ) \ (0.3, ) 0 j 0 tively. We use a particle-particle/particle-mesh (P3M) N-body code to simulate the formation and evolu- tion of large-scale structure in the universe. We perform 1.1 ) 107 ray-tracing experiments for each model, by computing the Jacobian matrix along random lines of sight, using the multiple lensplane algorithm. From the results of these experiments, we calculate the probability distribution functions of the convergences, shears, and magni—cations, and their rms values. We —nd that the rms values of the convergence and shear agree with the predictions of a nonlinear analytical model. We also —nd that the probability distribution functions of the magni—cations k have a peak at values slightly smaller than k \ 1 and are strongly skewed toward large magni—cations. In particular, for the high-density () 0 \ 1) model, a power-law tail appears in the distribution function at large magni—cations for sources at red- shifts The rms values of the magni—cations essentially agree with the nonlinear analytical predic- z s ( 2. tions for sources at low redshift but exceed these predictions for high redshift sources, once the power-law tail appears. We study the eUect of magni—cation bias on the luminosity functions of high- redshift quasars, using the calculated probability distribution functions of the magni—cations. We show that the magni—cation bias is moderate in the absence of the power-law tail in the magni—cation dis- tribution but depends strongly on the value of the density parameter In presence of the power-law ) 0 . tail, the bias becomes considerable, especially at the bright end of the luminosity functions where its logarithmic slope steepens. We present a speci—c example that demonstrates that the bias —attens the bright-side logarithmic slope of a double power-law luminosity function. Subject headings: cosmology: observationscosmology: theorydark matter ¨ gravitational lensinglarge-scale structure of universequasars: general
123302488
Behavior of Bianchi type I spacetime by path integral approach in LQC
119356150
Thermal hair of a quantum black hole
We investigate the possibility of statistical explanation of the black hole entropy by counting quasi-bounded modes of thermal fluctuation in two dimensional black hole spacetime. The black hole concerned is quantum in the sense that it is in thermal equilibrium with its Hawking radiation. It is shown that the fluctuation around such a black hole obeys a wave equation with a potential whose peaks are located near the black hole and which is caused by quantum effect. We can construct models in which the potential in the above sense has several positive peaks and there are quai-bounded modes confined between these peaks. This suggests that these modes contribute to the black hole entropy. However it is shown that the entropy associated with these modes dose not obey the ordinary area law. Therefore we can call these modes as an additional thermal hair of the quantum black hole.
18563380
Gravitational Lensing Effect on the Two-Point Correlation Function of Hot Spots in 21 cm fluctuations
We investigate the weak gravitational lensing effect on the two-point correlation function of local maxima (hot spots) in the cosmic 21 cm fluctuation map. The intrinsic two-point function has a pronounced depression feature around the angular scale of $\theta \sim 40$ arcmin, which depends on the observed frequency and corresponds to the scale of the acoustic oscillation of cosmic plasma before the recombination. It is found that the weak lensing induces a large w-dependent smoothing at that scale where w is the equation of state parameter of dark energy and thus provides a useful constraints on the dark energy property combined with the depression angular scales on the two-point correlation function.
8761976
The Post-Newtonian Approximation for Relativistic Compact Binaries
We discuss various aspects of the post-Newtonian approximation in general relativity. After presenting the foundation based on the Newtonian limit, we show a method to derive post-Newtonian equations of motion for relativistic compact binaries based on a surface integral approach and the strong field point particle limit. As an application we derive third post-Newtonian equations of motion for relativistic compact binaries which respect the Lorentz invariance in the post-Newtonian perturbative sense, admit a conserved energy, and are free from any ambiguity.
118896241
Numerical analysis of quasinormal modes in nearly extremal Schwarzschild–de Sitter spacetimes
We calculate high-order quasinormal modes with large imaginary frequencies for electromagnetic and gravitational perturbations in nearly extremal Schwarzschild-de Sitter spacetimes. Our results show that for low-order quasinormal modes, the analytical approximation formula in the extremal limit derived by Cardoso and Lemos is a quite good approximation for the quasinormal frequencies as long as the model parameter $r_1\kappa_1$ is small enough, where $r_1$ and $\kappa_1$ are the black hole horizon radius and the surface gravity, respectively. For high-order quasinormal modes, to which corresponds quasinormal frequencies with large imaginary parts, on the other hand, this formula becomes inaccurate even for small values of $r_1\kappa_1$. We also find that the real parts of the quasinormal frequencies have oscillating behaviors in the limit of highly damped modes, which are similar to those observed in the case of a Reissner-Nordstr{\" o}m black hole. The amplitude of oscillating ${\rm Re(\omega)}$ as a function of ${\rm Im}(\omega)$ approaches a non-zero constant value for gravitational perturbations and zero for electromagnetic perturbations in the limit of highly damped modes, where $\omega$ denotes the quasinormal frequency. This means that for gravitational perturbations, the real part of quasinormal modes of the nearly extremal Schwarzschild-de Sitter spacetime appears not to approach any constant value in the limit of highly damped modes. On the other hand, for electromagnetic perturbations, the real part of frequency seems to go to zero in the limit.
2149800
X-Ray Flashes from Off-Axis Gamma-Ray Bursts
K. Ioka and T. Nakamura proposed a simple jet model that is compatible with the peak luminosity-spectral lag relation, the peak luminosity-variability relation, and various other relations in the gamma-ray bursts. If the viewing angle is much larger than the collimation angle of the jet in the model by Ioka and Nakamura, for appropriate model parameters we obtain the observational characteristics of the X-ray flashes, such as the peak flux ratio and the fluence ratio between the ?-ray (50-300 keV) and the X-ray (2-10 keV) band, the X-ray photon index, the typical duration, and the event rate, ~100 yr-1. In our model, if the distance to the X-ray flashes is much larger than ~1 Gpc (or z 0.2) they are too dim to be observed, so the spatial distribution of the X-ray flashes should be homogeneous and isotropic.
14074558
General Relativistic Numerical Simulation on Coalescing Binary Neutron Stars and Gauge-Invariant Gravitational Wave Extraction
We are developing 3 dimensional simulation codes for coalescing binary neutron stars. A code using the maximal slicing condition is obtained. To evaluate the gravitational radiation, we implemented a gauge-invariant wave extraction and compared the wave forms with the metric tensors at the wave zone. The energy spectrum of the waves was also evaluated to investigate the possibility that the excitation of the quasi-normal modes of the black hole, which may be formed after the merger of two stars, can be observed.
17494376
Hydrodynamic time scales and temporal structure of GRBs
We calculate the hydrodynamic time scales for a spherical ultra-relativistic shell that is decelerated by the ISM and discuss the possible relations between these time scales and the observed temporal structure in γ-ray bursts. We suggest that the bursts’ durations are related to the deceleration time, the variations are related to the ISM inhomogeneities and precursors are related to internal shocks within the shell. Good agreement can be achieved for these quantities with reasonable, not fined tuned, astrophysical parameters. The difference between Newtonian and relativistic reverse shocks may lead to the observed bimodal distribution of bursts’ durations.
15565151
Gamma-ray bursts in 1.8 < z < 5.6 suggest that the time variation of the dark energy is small
We calibrated the peak energy–peak luminosity relation of gamma-ray bursts (GRBs; the so-called Yonetoku relation) using 33 events with redshift z < 1.62 without assuming any cosmological models. The luminosity distances to GRBs are estimated from those of large numbers of Type Ia supernovae with z < 1.755. This calibrated Yonetoku relation can be used as a new cosmic distance ladder towards higher redshifts. We determined the luminosity distances of 30 GRBs in 1.8 < z < 5.6 using the calibrated relation, and plotted the likelihood contour in the (Ωm, ΩΛ) plane. We obtained (Ωm, ΩΛ) = (0.37+0.14−0.11, 0.63+0.11−0.14) for a flat universe. Because our method is free from the circularity problem, we can say that our universe in 1.8 < z < 5.6 is compatible with the so-called concordance cosmological model derived for z < 1.8. This suggests that the time variation of the dark energy is small or zero up to z∼ 6.
27096862
Which Constituent Quark Model is Better
A comparative study has heen done by calculating the effective baryon-baryon interactions of the 64 lowest channels consisting of octet and decuplet baryons with three constituent quark models: the extended quark gluon exchange model, the Goldstone boson exchange model and the quark gluon meson exchange hybrid model. We find that these three models give similar results for 44 channels. Further tests of these models are discussed.