Using the standard Wentzel-Kramers-Brillouin method,the Wheeler-DeWitt equation for the Brans-Dicke theory is solved under three kinds of boundary conditions(proposed by Hartle-Hawking,Vilenkin and Linde,respectively)...Using the standard Wentzel-Kramers-Brillouin method,the Wheeler-DeWitt equation for the Brans-Dicke theory is solved under three kinds of boundary conditions(proposed by Hartle-Hawking,Vilenkin and Linde,respectively).It is found that,although the gravitational and cosmological“constants”are dynamical and time-dependent in the classical models,they will acquire constant values when the universe comes from the quantum creation,and that in particular,the amplitude of the resulting wave function under Linde or Vilenkin boundary conditions reaches its maximum if the cosmological constant is the minimum.展开更多
An independent method is proposed to determine the equation of state, ωx ≡ px/ρx, for the dark energy component in the universe. This method is based on gravitational lensing statistics. An analytically simple expr...An independent method is proposed to determine the equation of state, ωx ≡ px/ρx, for the dark energy component in the universe. This method is based on gravitational lensing statistics. An analytically simple expression for the optical depth of gravitational lensing in general Friedmann-Robertson- Walker cosmologies with dark energy component is derived. It is shown that for a flat universe the optical depth depends sensitively on the redshift to the source zs and the equation of state ωx which makes the method proposed here efficient and robust.展开更多
An independent method is proposed to estimate the dispersion velocity of galactic dark matter particles.This method is based on the observed quasar-galaxy association samples that are caused by gravitational lensing.A...An independent method is proposed to estimate the dispersion velocity of galactic dark matter particles.This method is based on the observed quasar-galaxy association samples that are caused by gravitational lensing.All resulting dispersion velocities are much higher than-220km·s^(-1),a value expected from the virial theorem,which shows that the conventional assumption of virialization may be invalid in the halo regions of galaxies.展开更多
The past decades have witnessed a lot of progress in gravitational lensing with two main targets:stars and galaxies(with active galactic nuclei).The success is partially attributed to the continuous luminescence of th...The past decades have witnessed a lot of progress in gravitational lensing with two main targets:stars and galaxies(with active galactic nuclei).The success is partially attributed to the continuous luminescence of these sources making the detection and monitoring relatively easy.With the running of ongoing and upcoming large facilities/surveys in various electromagnetic and gravitational-wave bands,the era of time-domain surveys would guarantee constant detection of strongly lensed explosive transient events,for example,supernovae in all types,gamma ray bursts with afterglows in all bands,fast radio bursts,and even gravitational waves.Lensed transients have many advantages over the traditional targets in studying the Universe,and magnification effect helps to understand the transients themselves at high redshifts.In this review article,on base of the recent achievements in literature,we summarize the methods of searching for different kinds of lensed transient signals,the latest results on detection and their applications in fundamental physics,astrophysics,and cosmology.At the same time,we give supplementary comments as well as prospects of this emerging research direction that may help readers who are interested in entering this field.展开更多
The weak gravity conjecture is proposed as a criterion to distinguish the landscape from the swampland in string theory. As an application in cosmology of this conjecture, we use it to impose theoretical constraint on...The weak gravity conjecture is proposed as a criterion to distinguish the landscape from the swampland in string theory. As an application in cosmology of this conjecture, we use it to impose theoretical constraint on parameters of the Chaplygin-gas-type models. Our analysis indicates that the Chaplygin-gas-type models realized in quintessence field are in the swampland.展开更多
After inversing the x-ray surface brightness of the cooling flow cluster Abell 1689 through the isothermal β model,the isothermal double β model and the x-ray surface brightness distribution model derived from the u...After inversing the x-ray surface brightness of the cooling flow cluster Abell 1689 through the isothermal β model,the isothermal double β model and the x-ray surface brightness distribution model derived from the universal dark matter density profile,we calculate the electron distribution and the Sunyaev-Zel'dovich(SZ)effect of the cluster.The resulting temperature decrements,which are inversely proportional to the square root of H0,are very different for the three models,with uncertainty of 15%.Thus,the SZ/x-ray route can not be taken as a precise measurement of H0 until further observations(e.g.from the satellite AXAF)constrain well the amount and distribution of cluster gas.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.19903002。
文摘Using the standard Wentzel-Kramers-Brillouin method,the Wheeler-DeWitt equation for the Brans-Dicke theory is solved under three kinds of boundary conditions(proposed by Hartle-Hawking,Vilenkin and Linde,respectively).It is found that,although the gravitational and cosmological“constants”are dynamical and time-dependent in the classical models,they will acquire constant values when the universe comes from the quantum creation,and that in particular,the amplitude of the resulting wave function under Linde or Vilenkin boundary conditions reaches its maximum if the cosmological constant is the minimum.
基金the National Natural Science Foundation of China under Grant No.19903002.
文摘An independent method is proposed to determine the equation of state, ωx ≡ px/ρx, for the dark energy component in the universe. This method is based on gravitational lensing statistics. An analytically simple expression for the optical depth of gravitational lensing in general Friedmann-Robertson- Walker cosmologies with dark energy component is derived. It is shown that for a flat universe the optical depth depends sensitively on the redshift to the source zs and the equation of state ωx which makes the method proposed here efficient and robust.
基金Supported by the National Natural Science Foundation of China under Grant No.19745008the China Postdoctorial Science FcMindation.
文摘An independent method is proposed to estimate the dispersion velocity of galactic dark matter particles.This method is based on the observed quasar-galaxy association samples that are caused by gravitational lensing.All resulting dispersion velocities are much higher than-220km·s^(-1),a value expected from the virial theorem,which shows that the conventional assumption of virialization may be invalid in the halo regions of galaxies.
基金supported by the National Natural Science Foundation of China(Grant Nos.12222302,11603015,12021003,11920101003,and 11633001)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB23000000)。
文摘The past decades have witnessed a lot of progress in gravitational lensing with two main targets:stars and galaxies(with active galactic nuclei).The success is partially attributed to the continuous luminescence of these sources making the detection and monitoring relatively easy.With the running of ongoing and upcoming large facilities/surveys in various electromagnetic and gravitational-wave bands,the era of time-domain surveys would guarantee constant detection of strongly lensed explosive transient events,for example,supernovae in all types,gamma ray bursts with afterglows in all bands,fast radio bursts,and even gravitational waves.Lensed transients have many advantages over the traditional targets in studying the Universe,and magnification effect helps to understand the transients themselves at high redshifts.In this review article,on base of the recent achievements in literature,we summarize the methods of searching for different kinds of lensed transient signals,the latest results on detection and their applications in fundamental physics,astrophysics,and cosmology.At the same time,we give supplementary comments as well as prospects of this emerging research direction that may help readers who are interested in entering this field.
基金Supported by the National Natural Science Foundation of China under Grant No 10533010, the National Basic Research Programme of China under Grant No 2007CB815401, and the Programme for New Century Excellent Talents in University of China. We thank Yi-Fu Cai and Yin-Zhe Ma for helpful discussions. We are also grateful to Neven Bilid, Gary Tupper and Raoul Viollier for pointing out some misunderstandings.
文摘The weak gravity conjecture is proposed as a criterion to distinguish the landscape from the swampland in string theory. As an application in cosmology of this conjecture, we use it to impose theoretical constraint on parameters of the Chaplygin-gas-type models. Our analysis indicates that the Chaplygin-gas-type models realized in quintessence field are in the swampland.
基金Supported by the National Natural Science Foundation of China under Grant No.19903002.
文摘After inversing the x-ray surface brightness of the cooling flow cluster Abell 1689 through the isothermal β model,the isothermal double β model and the x-ray surface brightness distribution model derived from the universal dark matter density profile,we calculate the electron distribution and the Sunyaev-Zel'dovich(SZ)effect of the cluster.The resulting temperature decrements,which are inversely proportional to the square root of H0,are very different for the three models,with uncertainty of 15%.Thus,the SZ/x-ray route can not be taken as a precise measurement of H0 until further observations(e.g.from the satellite AXAF)constrain well the amount and distribution of cluster gas.
