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朱宗宏, Zong-Hong Zhu
The Astrophysical Journal, 620: 7-11, 2005 February 10,-0001,():
-1年11月30日
There is mounting observational evidence that the expansion of our universe is undergoing anacceleration. A dark energy component has usually been invoked as the most feasible mechanism for the acceleration. However, it is desirable to explore alternative possibilitiesmotivated by particle physics before adopting such an untested entity. In this work, we focus our attention on an acceleration mechanism arising from gravitational leakage into extra dimensions. We test this scenario with high-z Type Ia supernovae compiled by Tonry and coworkers and recent measurements of the X-ray gas mass fractions in clusters of galaxies published by Allen and coworkers. A combination of the two databases gives, at a 99% confidence level, m
parameters-cosmology, theory-distance scale- supernovae, general-X-rays, galaxies, clusters
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【期刊论文】OBSERVATIONAL CONSTRAINTS ON COSMOLOGY FROM THE MODIFIED FRIEDMANN EQUATION
朱宗宏, Zong-Hong Zhu, Masa-Katsu Fujimoto, and Xiang-Tao He
The Astrophysical Journal, 603: 365-370, 2004 march 10,-0001,():
-1年11月30日
Recent measurements of Type Ia supernovae, as well as other concordant observations, suggest that the expansion of our universe is accelerating. A dark energy component has usually been invoked as the most feasible mechanism for the acceleration. However, effects arising from possible extra dimensions can mimic dark energy through a modified Friedmann equation. In this work, we investigate some observational constraints on ascenario in which this modification is given by H2
cosmological parameters-cosmology, theory-distance scale-supernovae, general-X-rays, galaxies, clusters
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朱宗宏, Zong-Hong Zhu
The Astrophysical Journal, 602: 12-17, 2004 february 10,-0001,():
-1年11月30日
Cosmic acceleration is one of the most remarkable cosmological findings of recent years. Although a dark energy component has usually been invoked as the mechanism for the acceleration, a modification of the Friedmann equation from various higher dimensional models provides a feasible alternative. Cardassian expansion is one of these scenarios, in which the universe is flat, matter (and radiation) dominated, and accelerating but contains no dark energy component. This scenario is fully characterized by n, the power index of the socalled Cardassian term in the modified Friedmann equation, and m, the matter density parameter of the universe. In this work, we first consider the constraints on the parameter space from the turnaround redshift, zq
cosmic microwave background-cosmology, theory-distance scale-galaxies, clusters, general
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朱宗宏, Z. H. Zhu
A&A 423, 421-426 (2004),-0001,():
-1年11月30日
Although various cosmological observations congruously suggest that our universe is dominated by two dark components, the cold dark matter without pressure and the dark energy with negative pressure, the nature and origin of these components is yet unknow. The generalized Chaplygin gas (gCg), parametrized by an equation of state, p=−A/ρα gCg, was recently proposed to be a candidate of the unified dark matter/energy (UDME) scenarios. In this work, we investigate some observational constraints on it. We mainly focus our attention on the constraints from recent measurements of the X-ray gas mass fractions in clusters of galaxies published by Allen et al. (2002,MNRAS, 334, L11; 2003, 342, 257) and the dimensionless coordinate distances to type Ia supernovae and Fanaro Riley type IIb radio galaxies compiled by Daly & Djorgovski (2003, ApJ, 597, 9). We obtain the confidence region on the two parameters fully characterizing gCg, As ≡ A/ρ(1+α) gCg0 and α, from a combined analysis of these databases, where ρgCg0 is the energy density of gCg at present. It is found that As=0.70+0.16−0.17 and −0.33, at a 95% confidence level, which is consistent within the errors with the standard dark matter+ dark energy model, i.e., the case of α=0. Particularly, the standard Chaplygin gas (α=1) is ruled out as a feasible UDME by the data at a 99% confidence level.
cosmology, cosmological parameters-cosmology, theory-stars: supernovae, general-galaxies, distances and redshifts-X-rays, galaxies, clusters
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朱宗宏, Zong-Hong Zhu, Masa-Katsu Fujimoto, and Xiang-Tao He
A&A 417, 833-837 (2004),-0001,():
-1年11月30日
Using recent measurements of angular size of high-z milliarcsecond compact radio sources compiled by Gurvitset al. (1999) and X-ray gas mass fraction of galaxy clusters published by Allen et al. (2002, 2003), we explore their bounds on the equation of state, ωx=px/ρx, of the dark energy, whose existence has been congruously suggested by various cosmological observations. We relax the usual constraint ωx ≥ −1, and find that combining the two databases yields a nontrivial lower bound on ωx. Under the assumption of a flat universe, we obtain a bound −2.22<ωx<−0.62 at 95.4% confidence level. The 95.4% confidence bound goes to −1 ≤ωx<−0.60 when the constraint ωx ≥ −1 is imposed.
cosmology, cosmological parameters-cosmology, theory-cosmology, distance scale-galaxies, active-radio continuum, galaxies-X-ray, galaxies, clusters
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