We develop methods to extract key dark energy information from cosmic distance measurements including the BAO scales and supernova(SN) luminosity distances.Demonstrated using simulated data sets of the complete DESI,L...We develop methods to extract key dark energy information from cosmic distance measurements including the BAO scales and supernova(SN) luminosity distances.Demonstrated using simulated data sets of the complete DESI,LSST and Roman surveys designed for BAO and SN distance measurements,we show that using our method,the dynamical behavior of the energy,pressure,equation of state(with its time derivative) of dark energy and the cosmic deceleration function can all be accurately recovered from high-quality data,which allows for robust diagnostic tests for dark energy models.展开更多
The space environment background of various particle fluxes of the Hard X-ray Imager(HXI), one of the payloads of the Advanced Space-based Solar Observatory(ASO-S) spacecraft, is investigated and presented. Different ...The space environment background of various particle fluxes of the Hard X-ray Imager(HXI), one of the payloads of the Advanced Space-based Solar Observatory(ASO-S) spacecraft, is investigated and presented. Different approaches are used to obtain the input information on various space environment particles(protons, alpha particles, electrons, positrons, neutrons, and photons). Some special regions(SAA and radiation belt) are also taken into account. The findings indicate that electrons are the primary background source in the radiation belt. Due to the large background flux generated by electrons, HXI cannot effectively observe solar flares in the radiation belt.Outside the radiation belt, primary protons and albedo photons are the main sources of background at low and high magnetic latitudes respectively. The statistical analysis of the flare and background spectra shows that the errors of the flare energy spectrum observation are mainly concentrated in the high energy band, and the detector still has a certain spectrum observation capability for flares of C-class and below in the low energy band of the non-radiation belt. The imaging observation of flares of C-class and below is significantly affected by the accuracy of background subtraction. The energy band with the best signal-to-noise ratio is from 10 to 50 ke V, which can be used to monitor the formation and class of flares.展开更多
The observed microwave background radiation （MBR） is commonly in- terpreted as the relic of an early hot universe, and its observed features （spectrum and anisotropy） are explained in terms of properties of the ea...The observed microwave background radiation （MBR） is commonly in- terpreted as the relic of an early hot universe, and its observed features （spectrum and anisotropy） are explained in terms of properties of the early universe. Here we describe a complementary, even possibly alternative, interpretation of MBR, first proposed in the early 20th century, and adapt it to modern observations. For example, the stellar Hipparcos data show that the energy density of starlight from the Milky Way, if suit- ably thermalized, yields a temperature of ~2.81 K. This and other arguments given here strongly suggest that the origin of MBR may lie, at least in a very large part, in re-radiation of thermalized galactic starlight. The strengths and weaknesses of this alternative radical explanation are discussed.展开更多
There continues to be good reason to believe that dark matter particles,which only"feel"the gravitational force,influence the local and distant Universe,despite drawing a complete blank in the search for suc...There continues to be good reason to believe that dark matter particles,which only"feel"the gravitational force,influence the local and distant Universe,despite drawing a complete blank in the search for such a particle.The expansion rate of the Universe is defined by the Hubble constant h.Measurements of the Hubble constant at different wavelengths produce different results,differing well beyond their errors.Here it is shown that the two precise but different values for the Hubble constant can be used to derive the mass of a weakly interacting massive particle(WIMP).An approximate mass of 1022 eV is determined with indications of why,so far,it has not been found and what is required to get positive confirmation of its presence.This result also indicates that the Hubble constant is the sum of more than one contribution with suggestions for experimental tests to determine,more precisely,the level of these contributions.展开更多
One of the main goals of modern cosmic microwave background （CMB） missions is to measure the tensor-to-scalar ratio r accurately to constrain inflation models. Due to ignorance about the reionization history Xe （z...One of the main goals of modern cosmic microwave background （CMB） missions is to measure the tensor-to-scalar ratio r accurately to constrain inflation models. Due to ignorance about the reionization history Xe （z）, this analysis is usu- ally done by assuming an instantaneous reionization Xe （z） which, however, can bias the best-fit value of r. Moreover, due to the strong mixing of B-mode and E-mode polarizations in cut-sky measurements, multiplying the sky coverage fraction fsky by the full-sky likelihood would not give satisfactory results. In this work, we forecast constraints on r for the Planck mission taking into account the general reionization scenario and cut-sky effects. Our results show that by applying an N-point interpo- lation analysis to the reionization history, the bias induced by the assumption of in- stantaneous reionization is removed and the value of r is constrained within 5% error level, if the true value of r is greater than about 0.1.展开更多
We investigate large-angle scale temperature anisotropy in the Cosmic Microwave Background （CMB） with the Wilkinson Microwave Anisotropy Probe （WMAP） data and model the large-angle anomalies as the effect of the C...We investigate large-angle scale temperature anisotropy in the Cosmic Microwave Background （CMB） with the Wilkinson Microwave Anisotropy Probe （WMAP） data and model the large-angle anomalies as the effect of the CMB quadrupole anisotropies caused by the local density inhomogeneities. The quadrupole caused by the local density inhomogeneities is different from the special relativity kinematic quadrupole. If the observer inhabits a strong inhomogeneous region, the lo- cal quadrupole should not be neglected. We calculate such local quadrupole under the assumption that there is a huge density fluctuation field in the direction （284°, 74°）, where the density fluctuation is 10-3, and its center is - 112 h-1 Mpc away from us. After removing such mock signals from WMAP data, the power in the quadrupole, C2, increases from the range （200 - 260 μK2） to - 1000 μK2. The quantity S, which is used to estimate the alignment between the quadrupole and the octopole, decreases from （0.7 - 0.74） to （0.31 - 0.37）, while the model predicts that C2 = 1071.5 μK2, and S = 0.412. So our local density inhomogeneity model can, in part, explain the WMAP low-l anomalies.展开更多
Both the Wilkinson Microwave Anisotropy Probe （WMAP） and Planck missions have reported an extremely cold spot （CS） centered at Galactic coordinate （1 = 209°, b = -57°） in the cosmic microwave backgroun...Both the Wilkinson Microwave Anisotropy Probe （WMAP） and Planck missions have reported an extremely cold spot （CS） centered at Galactic coordinate （1 = 209°, b = -57°） in the cosmic microwave background map. We study the lo- cal non-Gaussianity of the CS by defining local Minkowski functionals. We find that the third Minkowski functional v2 is quite sensitive to the non-Gaussianity caused by the CS. Compared with random Gaussian simulations, the WMAP CS deviates from Gaussianity at more than a 99% confidence level with a scale of R - 10°. Meanwhile, we find that cosmic texture provides an excellent explanation for these anomalies re- lated to the WMAP CS, which could be further tested by future polarization data.展开更多
Abstract We use the recently released data of lookback time （LT）-redshift relation, the cosmic microwave background shift parameter and the baryon acoustic oscillation measurements to constrain cosmological paramete...Abstract We use the recently released data of lookback time （LT）-redshift relation, the cosmic microwave background shift parameter and the baryon acoustic oscillation measurements to constrain cosmological parameters of f（R） gravity in the Palatini formalism by considering the f（R） form of type（a）f（R） = R -β/Rn and （b）f（R） = R ＋ αIn R - β. Under the assumption of a Friedmann-Robertson-Walker universe, we achieved the best fitting results of the free parameters （Ωm0, n） for （a） and （Ωm0, α） for （b）. We find that current LT data can provide interesting and effective constraints on gravity models. Compared with other data, the LT constraints favor a smaller value of the non-relativistic matter energy density.展开更多
基金supported by the National Key R&D Program of China(2023YFA1607800,2023YFA1607803)the National Natural Science Foundation of China (NSFC,Grant Nos.11925303 and11890691)+3 种基金supported by the National Natural Science Foundation of China (NSFC,Grant No.12203062)by a CAS Project for Young Scientists in Basic Research (No.YSBR-092)supported by science research grants from the China Manned Space Project with No.CMS-CSST-2021-B01supported by the New Cornerstone Science Foundation through the XPLORER prize。
文摘We develop methods to extract key dark energy information from cosmic distance measurements including the BAO scales and supernova(SN) luminosity distances.Demonstrated using simulated data sets of the complete DESI,LSST and Roman surveys designed for BAO and SN distance measurements,we show that using our method,the dynamical behavior of the energy,pressure,equation of state(with its time derivative) of dark energy and the cosmic deceleration function can all be accurately recovered from high-quality data,which allows for robust diagnostic tests for dark energy models.
基金supported by the Strategic Priority Research Program on Space Science,Chinese Academy of Sciences (No.XDA 15 320 104)National Natural Science Foundation of China (NSFC, Grant Nos. 11973097, 12173100 and 12022302)the Youth Innovation Promotion Association CAS (Nos.2021317 and Y2021087)。
文摘The space environment background of various particle fluxes of the Hard X-ray Imager(HXI), one of the payloads of the Advanced Space-based Solar Observatory(ASO-S) spacecraft, is investigated and presented. Different approaches are used to obtain the input information on various space environment particles(protons, alpha particles, electrons, positrons, neutrons, and photons). Some special regions(SAA and radiation belt) are also taken into account. The findings indicate that electrons are the primary background source in the radiation belt. Due to the large background flux generated by electrons, HXI cannot effectively observe solar flares in the radiation belt.Outside the radiation belt, primary protons and albedo photons are the main sources of background at low and high magnetic latitudes respectively. The statistical analysis of the flare and background spectra shows that the errors of the flare energy spectrum observation are mainly concentrated in the high energy band, and the detector still has a certain spectrum observation capability for flares of C-class and below in the low energy band of the non-radiation belt. The imaging observation of flares of C-class and below is significantly affected by the accuracy of background subtraction. The energy band with the best signal-to-noise ratio is from 10 to 50 ke V, which can be used to monitor the formation and class of flares.
基金supported in part by the Perimeter Institute for Theoretical PhysicsResearch at the Perimeter Institute is supported by the Government of Canada through Industry Canadaby the Province of Ontario through the Ministry of Research and Innovation
文摘The observed microwave background radiation （MBR） is commonly in- terpreted as the relic of an early hot universe, and its observed features （spectrum and anisotropy） are explained in terms of properties of the early universe. Here we describe a complementary, even possibly alternative, interpretation of MBR, first proposed in the early 20th century, and adapt it to modern observations. For example, the stellar Hipparcos data show that the energy density of starlight from the Milky Way, if suit- ably thermalized, yields a temperature of ~2.81 K. This and other arguments given here strongly suggest that the origin of MBR may lie, at least in a very large part, in re-radiation of thermalized galactic starlight. The strengths and weaknesses of this alternative radical explanation are discussed.
基金the support given by the Fred Hoyle Cosmology Club。
文摘There continues to be good reason to believe that dark matter particles,which only"feel"the gravitational force,influence the local and distant Universe,despite drawing a complete blank in the search for such a particle.The expansion rate of the Universe is defined by the Hubble constant h.Measurements of the Hubble constant at different wavelengths produce different results,differing well beyond their errors.Here it is shown that the two precise but different values for the Hubble constant can be used to derive the mass of a weakly interacting massive particle(WIMP).An approximate mass of 1022 eV is determined with indications of why,so far,it has not been found and what is required to get positive confirmation of its presence.This result also indicates that the Hubble constant is the sum of more than one contribution with suggestions for experimental tests to determine,more precisely,the level of these contributions.
基金partially supported by a grant from the Research Grant Councilof the Hong Kong Special Administrative Region,China(Project No.400910)the support of a postdoctoral fellowship by The Chinese University of Hong Kong
文摘One of the main goals of modern cosmic microwave background （CMB） missions is to measure the tensor-to-scalar ratio r accurately to constrain inflation models. Due to ignorance about the reionization history Xe （z）, this analysis is usu- ally done by assuming an instantaneous reionization Xe （z） which, however, can bias the best-fit value of r. Moreover, due to the strong mixing of B-mode and E-mode polarizations in cut-sky measurements, multiplying the sky coverage fraction fsky by the full-sky likelihood would not give satisfactory results. In this work, we forecast constraints on r for the Planck mission taking into account the general reionization scenario and cut-sky effects. Our results show that by applying an N-point interpo- lation analysis to the reionization history, the bias induced by the assumption of in- stantaneous reionization is removed and the value of r is constrained within 5% error level, if the true value of r is greater than about 0.1.
文摘We investigate large-angle scale temperature anisotropy in the Cosmic Microwave Background （CMB） with the Wilkinson Microwave Anisotropy Probe （WMAP） data and model the large-angle anomalies as the effect of the CMB quadrupole anisotropies caused by the local density inhomogeneities. The quadrupole caused by the local density inhomogeneities is different from the special relativity kinematic quadrupole. If the observer inhabits a strong inhomogeneous region, the lo- cal quadrupole should not be neglected. We calculate such local quadrupole under the assumption that there is a huge density fluctuation field in the direction （284°, 74°）, where the density fluctuation is 10-3, and its center is - 112 h-1 Mpc away from us. After removing such mock signals from WMAP data, the power in the quadrupole, C2, increases from the range （200 - 260 μK2） to - 1000 μK2. The quantity S, which is used to estimate the alignment between the quadrupole and the octopole, decreases from （0.7 - 0.74） to （0.31 - 0.37）, while the model predicts that C2 = 1071.5 μK2, and S = 0.412. So our local density inhomogeneity model can, in part, explain the WMAP low-l anomalies.
基金Supported by the National Natural Science Foundation of China
文摘Both the Wilkinson Microwave Anisotropy Probe （WMAP） and Planck missions have reported an extremely cold spot （CS） centered at Galactic coordinate （1 = 209°, b = -57°） in the cosmic microwave background map. We study the lo- cal non-Gaussianity of the CS by defining local Minkowski functionals. We find that the third Minkowski functional v2 is quite sensitive to the non-Gaussianity caused by the CS. Compared with random Gaussian simulations, the WMAP CS deviates from Gaussianity at more than a 99% confidence level with a scale of R - 10°. Meanwhile, we find that cosmic texture provides an excellent explanation for these anomalies re- lated to the WMAP CS, which could be further tested by future polarization data.
基金supported by the National Natural Science Foundation of China(Grant Nos.10773002 and 10875012)supported by the Fundamental Research Funds for the Central Universities(Grant No.105116)
文摘Abstract We use the recently released data of lookback time （LT）-redshift relation, the cosmic microwave background shift parameter and the baryon acoustic oscillation measurements to constrain cosmological parameters of f（R） gravity in the Palatini formalism by considering the f（R） form of type（a）f（R） = R -β/Rn and （b）f（R） = R ＋ αIn R - β. Under the assumption of a Friedmann-Robertson-Walker universe, we achieved the best fitting results of the free parameters （Ωm0, n） for （a） and （Ωm0, α） for （b）. We find that current LT data can provide interesting and effective constraints on gravity models. Compared with other data, the LT constraints favor a smaller value of the non-relativistic matter energy density.
