arXiv subjects

Wen-Fei Liu

Publications and source records attributed to Wen-Fei Liu.

6 recordsLinked to original sources

arXiv2025

Constraints on Baryon Density from the Effective Optical Depth of High-Redshift Quasars

We present constraints on the baryonic matter density parameter, $Ω_b$, within the framework of the $Λ$CDM model. Our analysis utilizes observational data on the effective optical depth from high-redshift quasars. To parameterize the photoionization rate $Γ_{-12}$, we employ a Bézier polynomial. Additionally, we approximate the Hubble parameter at high redshifts as $H(z)\approx 100hΩ_m^{1/2} (1+z)^{3/2}$ km s$^{-1}$ Mpc$^{-1}$. Confidence regions are obtained with $h=0.701\pm0.013$ and $Ω_m = 0.315$, optimized by the Planck mission. The best-fit values are $Ω_b =0.043^{+0.005}_{-0.006}$ and $Ω_b = 0.045^{+0.004}_{-0.006}$, corresponding to an old data set and a new data set, respectively. And we test the non-parametric form of $Γ_{-12}$, obtaining $Ω_b = 0.048^{+0.001}_{-0.003}$. These results are consistent with the findings of Planck at the 1 $σ$ confidence level. Our findings underscore the effectiveness of quasar datasets in constraining $Ω_b$, eliminating the need for independent photoionization rate data. This approach provides detailed cosmic information about baryon density and the photoionization history of the intergalactic medium.

astro-ph.CO↗

arXiv2023

Multibeam Blind Search of Targeted SETI Observations toward 33 Exoplanet Systems with FAST

The search for extraterrestrial intelligence (SETI) is to search for technosignatures associated with extraterrestrial life, such as engineered radio signals. In this paper, we apply the multibeam coincidence matching (MBCM) strategy, and propose a new search mode based on the MBCM which we call MBCM blind search mode. In our recent targeted SETI research, 33 exoplanet systems are observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). With this blind search mode, we search for narrowband drifting signals across $1.05-1.45$ GHz in two orthogonal linear polarization directions separately. There are two special signals, one of which can only be detected by the blind search mode while the other can be found by both blind and targeted search modes. This result reveals huge advantages of the new blind search mode. However, we eliminate the possibility of the special signals being ETI signals based on much evidence, such as the polarization, drift, frequency and beam coverage characteristics. Our observations achieve an unprecedented sensitivity and our work provides a deeper understanding to the polarization analysis of extraterrestrial signals.

astro-ph.EP↗

arXiv2022

Sensitive Multi-beam Targeted SETI Observations towards 33 Exoplanet Systems with FAST

As a major approach to looking for life beyond the Earth, the search for extraterrestrial intelligence (SETI) is committed to detecting technosignatures such as engineered radio signals that are indicative of technologically capable life. In this paper, we report a targeted SETI campaign employing an observation strategy named multi-beam coincidence matching (MBCM) at the Five-hundred-meter Aperture Spherical radio Telescope (FAST) towards 33 known exoplanet systems, searching for ETI narrow-band drifting signals across 1.05-1.45 GHz in two orthogonal linear polarization directions separately. A signal at 1140.604 MHz detected from the observation towards Kepler-438 originally peaked our interest because its features are roughly consistent with assumed ETI technosignatures. However, evidences such as its polarization characteristics are almost able to eliminate the possibility of an extraterrestrial origin. Our observations achieve an unprecedented sensitivity since the minimum equivalent isotropic radiated power (EIRP) we are able to detect reaches 1.48 x10^9 W.

astro-ph.EP↗

arXiv2021

Probing the time variation of fine structure constant using galaxy clusters and quintessence model

We explore a possible time variation of the fine structure constant ($α\equiv e^2/\hbar c$) using the Sunyaev-Zel'dovich effect measurements of galaxy clusters along with their X-ray observations. Specifically, the ratio of the integrated Compto-ionization parameter $Y_{SZ}D_A^2$ and its X-ray counterpart $Y_X$ is used as an observable to constrain the bounds on the variation of $α$. Considering the violation of cosmic distance duality relation, this ratio depends on the fine structure constant as $\sim α^3$. We use the quintessence model to provide the origin of $α$ time variation. In order to give a robust test on $α$ variation, two galaxy cluster samples, the 61 clusters provided by the Planck collaboration and the 58 clusters detected by the South Pole Telescope, are collected for analysis. Their X-ray observations are given by the XMM-Newton survey. Our results give $ζ=-0.203^{+0.101}_{-0.099}$ for the Planck sample and $ζ=-0.043^{+0.165}_{-0.148}$ for the SPT sample, indicating that $α$ is constant with redshift within $3σ$ and $1σ$ for the two samples, respectively.

astro-ph.CO↗

arXiv2021

SETI strategy with FAST fractality

We applied the Koch snowflake fractal antenna in planning calibration of the Five-hundred-meter Aperture Spherical radio Telescope (FAST), hypothesizing second-order fractal primary reflectors can optimize the orientated sensitivity of the telescope. Meanwhile, on the grounds of NASA Science Working Group Report in 1984, we reexamine the strategy of Search for Extraterrestrial Intelligence (SETI). A mathematical analysis of the radar equation will be performed in the first section, aiming to make it convenient to design a receiver system that can detect activities of an extraterrestrial civilization, according to the observable region of the narrowband. Taking advantage of the inherent potential of FAST, we simulate the theoretical detection of a Kardashev Type I civilization by a snowflake-selected reflecting area.

astro-ph.IM↗

arXiv2021

Energy conditions and entropy density of the universe

In the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological model, the energy conditions provides model-independent bounds on the behavior of the distance modulus. However, this method can not provide us the detailed information about the violation between the energy conditions and the observation. In this paper, we present an extended analysis of the energy conditions based upon the entropy density of the universe. On the one hand, we find that these conditions imply that entropy density s depends on Hubble parameter H(z). On the other hand, we compare the theoretical entropy density from the conservation law of energy-momentum tensor with that from the energy conditions using the observational Hubble parameter. When we consider a FLRW universe, according to the theoretical prediction, OHD, thermodynamics and several independent cosmological probes, show that the dominant energy condition is fitter than other energy conditions.

astro-ph.CO↗