arXiv subjects

Wen Zhao

Publications and source records attributed to Wen Zhao.

219 records · Page 13Linked to original sources

arXiv2005

Relic Gravitational Waves and the Evolution of the Universe

In the inflation models, the relic gravitational waves (RGW) generated in the inflation stage, and evolved in the Universe until now. In the different cosmological evolution models, one can get different gravitational waves power spectrum. In this paper, we give a simple formula to estimate this spectrum in a general cosmological model. From this formula, one can easily find the relation between this power spectrum and the cosmological evolution models. The spectrum includes all the information about the evolution of the scale factor $a$ from inflation to now. So RGW is a more clear fossil, which records the cosmological evolution information, and be a useful complementarity for another fossil$-$Cosmic Microwave Background Radiation (CMB).

astro-ph↗

arXiv2005

The Largest Scale We Can Detect in the Universe and the Inflation

From the damping of the Cosmic Microwave Background Radiation (CMB) anisotropy power spectrum at large scale and the recent accelerating expansion of the Universe, we find that, there may be a largest scale which we can detect in the Universe. From this, we can get the inflation parameters as spectrum index $n_s$, e-fold $N$, Hubble parameter $H$, the ratio of tensor and scalar $r$, the lasting time of reheating time $α$ for special inflation models. We do them in three inflation models, and find that all the results fit very well with the observations and the inflation theory.

astro-ph↗

arXiv2005

Relic Gravitational Waves in the Accelerating Universe

Observations have recently indicated that the Universe at the present stage is in an accelerating expansion, a process that has great implications. We evaluate the spectrum of relic gravitational waves in the current accelerating Universe and find that there are new features appearing in the resulting spectrum as compared to the decelerating models. In the low frequency range the peak of spectrum is now located at a frequency $ν_E \simeq (\frac{Ω_m}{Ω_Λ})^{1/3} ν_H$, where $ν_H$ is the Hubble frequency, and there appears a new segment of spectrum between $ν_E$ and $ν_H$. In all other intervals of frequencies $\geq ν_H$, the spectral amplitude acquires an extra factor $\frac{Ω_m}{Ω_Λ}$, due to the current acceleration, otherwise the shape of spectrum is similar to that in the decelerating models. The recent WMAP result of CMB anisotropies is used to normalize the amplitude for gravitational waves. The slope of the power spectrum depends sensitively on the scale factor $a(τ) \propto |τ|^{1+β}$ during the inflationary stage with $β=-2$ for the exact de Sitter space. With the increasing of $β$, the resulting spectrum is tilted to be flatter with more power on high frequencies, and the sensitivity of the second science run of the LIGO detectors puts a restriction on the parameter $β\leq -1.8$. We also give a numerical solution which confirms these features.

astro-ph↗