We use the latest baryon acoustic oscillation and Union 2.1 type Ia supernova data to test the cosmic opacity between different redshift regions without assuming any cosmological models. It is found that the universe ...We use the latest baryon acoustic oscillation and Union 2.1 type Ia supernova data to test the cosmic opacity between different redshift regions without assuming any cosmological models. It is found that the universe may be opaque between the redshift regions 0.35 0.44, 0.44 0.57 and 0.6-0.73 since the best fit values of cosmic opacity in these regions are positive, while a transparent universe is favored in the redshift region 0.57-0.63. However, in general, a transparent universe is still consistent with observations at the lo confidence level.展开更多
Gravitational field equations in Randers-Finsler space of approximate Berwald type are investigated. A modified Friedmann equation and a new luminosity distance-redshift relation is proposed. A best-fit to the Type Ia...Gravitational field equations in Randers-Finsler space of approximate Berwald type are investigated. A modified Friedmann equation and a new luminosity distance-redshift relation is proposed. A best-fit to the Type Ia supernovae （SNe） observations yields that the Λ in the Λ-CDM model is suppressed to almost zero. This fact indicates that the astronomical observations on the Type Ia SNe can be described well without invoking any form of dark energy. The best-fit age of the universe is given. It is in agreement with the age of our galaxy.展开更多
The equation of state(EoS) of dark energy plays an important role in the evolution of the universe and has attracted considerable interest in the recent years. With the progress in observational technique, a precise c...The equation of state(EoS) of dark energy plays an important role in the evolution of the universe and has attracted considerable interest in the recent years. With the progress in observational technique, a precise constraint on the EoS of dark energy can be obtained. In this study, we reconstruct the EoS of dark energy and cosmic expansion using Gaussian processes(GP) from the most up-to-date Pantheon compilation of type Ia supernovae(SNe Ia),which consists of 1048 finely calibrated SNe Ia. The reconstructed EoS of dark energy has a large uncertainty owing to its dependence on the second-order derivative of the construction. Adding the direct measurements of Hubble parameters H(z) as an additional constraint on the first-order derivative can partially reduce the uncertainty;however, it is still not sufficiently precise to distinguish between the evolving and the constant dark energy. Moreover, the results heavily rely on the prior of the Hubble constant H0. The H0 value inferred from SNe+ H(z) without prior is H0= 70.5 ± 0.5 km s^-1 Mpc^-1. Moreover, the matter density ΩM has a non-negligible effect on the reconstruction of dark energy. Therefore, more accurate determinations on H0 and ΩM are required to tightly constrain the EoS of dark energy.展开更多
Based on the idea of hypothetical 4-dimensial substance with an inverse population of energy levels, a model of accelerated expansion of the Universe has been developed, which describes Hubble diagrams with great accu...Based on the idea of hypothetical 4-dimensial substance with an inverse population of energy levels, a model of accelerated expansion of the Universe has been developed, which describes Hubble diagrams with great accuracy for type Ia supernovae, quasars and gamma-ray burst sources at the Hubble parameter value of 67.7 km/s/Mpc, coinciding with the value obtained from analysis of inhomogeneities of relic radiation. Calculations at the Hubble parameter value of 73.5 km/s/Mpc, obtained using the ΛCDM model based on the analysis of data on type Ia supernovae and cepheids, differ markedly from the observed data. An explanation of the two values of the Hubble constant is proposed. It is shown that in this model, the magnitude of 13.8 billion years characterizes not the age of the Universe, but the time of propagation of light from those galaxes whose acceleration of removal has a minimal value. Based on the recently discovered curvature of the Universe, estimates are given of the lower limits of its size and lifetime, which turned out to be at least 270 billon years. The probability of transition from the excited state to the underlying energy levels of a hypothetical 4-dimensial substance, as well as the low of increasing energy density as a result of transitions to the underlying levels of this substance, is determined.展开更多
We investigate the possible anisotropy of the universe using data on the most up-to-date type Ia supernovae,i.e.,the Pantheon+compilation.We fit the full Pantheon+data with the dipole-modulated ΛCDM model and find th...We investigate the possible anisotropy of the universe using data on the most up-to-date type Ia supernovae,i.e.,the Pantheon+compilation.We fit the full Pantheon+data with the dipole-modulated ΛCDM model and find that the data are well consistent with a null dipole.We further divide the full sample into several subsamples with different high-redshift cutoffs zc.It is shown that the dipole appears at the 2σ confidence level only if z_(c)≤0.1,and in this redshift region,the dipole is very stable,almost independent of the specific value of zc.For z_(c)=0.1,the dipole amplitude is D=1.0_(-0.4^(+0.4))×10^(-3),pointing toward(l,b)=(334.5°_(-21.6°)^(+25.7°),16.0°_(-16.8°)^(+27.1°)),which is approximately 65°away from the CMB dipole.This implies that the full Pantheon+sample is consistent with a large-scale isotropic universe,but the low-redshift anisotropy could not be purely explained by the peculiar motion of the local universe.展开更多
Realistic FLRW cosmic coasting models which contain matter now appear to be a reasonable alternative in explaining the accumulated Supernova Cosmology Project data since 1998. In sharp contrast to the unrealistic orig...Realistic FLRW cosmic coasting models which contain matter now appear to be a reasonable alternative in explaining the accumulated Supernova Cosmology Project data since 1998. In sharp contrast to the unrealistic original classic Milne universe, which was entirely devoid of matter, these modified Milne-type models containing matter, often referred to as realistic linear Rh = ct models, have rapidly become the primary competition with standard cosmology. This paper compares the expected relative luminosity distances and relative angular diameter distances for given magnitudes of redshift within these two competing models. A simple ratio formula is derived, which explains how expected luminosity distances and angular diameter distances for given magnitudes of redshift within a realistic Milne-type cosmic expansion could create the illusion (for standard model proponents) of cosmic acceleration where none exists.展开更多
In this work,we explore the cosmological consequences of the latest Type Ia supernova(SN Ia)dataset,Pantheon,by adopting the wCDM model.The Pantheon dataset currently contains the largest number of SN Ia samples,which...In this work,we explore the cosmological consequences of the latest Type Ia supernova(SN Ia)dataset,Pantheon,by adopting the wCDM model.The Pantheon dataset currently contains the largest number of SN Ia samples,which contains 1048 supernovae on the redshift range 0<z<2.3.Here we take into account three kinds of SN Ia statistics techniques,including:(1)magnitude statistics(MS),which is the traditional SN Ia statistics technique;(2)flux statistics(FS),which is based on the flux-averaging(FA)method;and(3)improved flux statistics(IFS),which combines the advantages of MS and FS.It should be mentioned that the IFS technique needs to scan the(zcut,Δz)parameters plane,where zcut andΔz are redshift cut-off and redshift interval of FA,respectively.The results are as follows.(1)Using the SN dataset only,the best FA recipe for IFS is(zcut,Δz)=(0.1,0.08);(2)comparing to the old SN dataset,JLA,adopting the Pantheon dataset can reduce the 2σerror bars of equation of state w by 38%,47%and 53%for MS,FS and IFS,respectively;(3)FS gives closer results to other observations,such as Baryon acoustic oscillations and cosmic microwave background;(4)compared with FS and IFS,MS more favors a Universe that will end in a‘big rip’.展开更多
Previous studies have shown that for the Supernova Legacy Survey three-year(SNLS3)data there is strong evidence for the redshiftevolution of color-luminosity parameterβof type Ia supernovae(SN Ia).In this paper,we ex...Previous studies have shown that for the Supernova Legacy Survey three-year(SNLS3)data there is strong evidence for the redshiftevolution of color-luminosity parameterβof type Ia supernovae(SN Ia).In this paper,we explore the effects of varyingβon the cosmological constraints of holographic dark energy(HDE)model.In addition to the SNLS3 data,we also use Planck distance prior data of cosmic microwave background(CMB),as well as galaxy clustering(GC)data extracted from Sloan Digital Sky Survey(SDSS)data release 7 and Baryon Oscillation Spectroscopic Survey(BOSS).We find that,for the both cases of using SN data alone and using SN+CMB+GC data,involving an additional parameter ofβcan reduceχ2by～36;this shows thatβdeviates from a constant at 6σconfidence levels.Adopting SN+CMB+GC data,we find that compared to the constantβcase,varyingβyields a larger fractional matter density-m0and a smaller reduced Hubble constant h;moreover,varyingβsignificantly increases the value of HDE model parameter c,leading to c≈0.8,consistent with the constraint results obtained before Planck.These results indicate that the evolution ofβshould be taken into account seriously in the cosmological fits.In addition,we find that relative to the differences between the constantβand varyingβ(z)cases,the effects of different light-curve fitters on parameter estimation are very small.展开更多
It has been found that, for the Supernova Legacy Survey three-year(SNLS3) data, there is strong evidence for the redshift-evolution of color-luminosity parameter β. In previous studies, only dark energy(DE) models ar...It has been found that, for the Supernova Legacy Survey three-year(SNLS3) data, there is strong evidence for the redshift-evolution of color-luminosity parameter β. In previous studies, only dark energy(DE) models are used to explore the effects of a time-varying β on parameter estimation. In this paper, we extend the discussions to the case of modified gravity(MG), by considering Dvali–Gabadadze–Porrati(DGP) model, power-law type f(T) model and exponential type f(T) model. In addition to the SNLS3 data, we also use the latest Planck distance priors data,the galaxy clustering(GC) data extracted from Sloan Digital Sky Survey(SDSS) data release 7(DR7) and Baryon Oscillation Spectroscopic Survey(BOSS), as well as the direct measurement of Hubble constant H0 from the Hubble Space Telescope(HST) observation. We find that, for both cases of using the supernova(SN) data alone and using the combination of all data, adding a parameter of β can reduce χ2by ～ 36 for all the MG models, showing that a constantβ is ruled out at 6σ confidence level(CL). Moreover, we find that a time-varying β always yields a larger fractional matter density Ωm0and a smaller reduced Hubble constant h; in addition, it significantly changes the shapes of 1σ and2σ confidence regions of various MG models, and thus corrects systematic bias for the parameter estimation. These conclusions are consistent with the results of DE models, showing that β's evolution is completely independent of the cosmological models in the background. Therefore, our work highlights the importance of considering the evolution of βin the cosmology-fits.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11175093,11222545,11435006 and 11375092the K.C.Wong Magna Fund of Ningbo University
文摘We use the latest baryon acoustic oscillation and Union 2.1 type Ia supernova data to test the cosmic opacity between different redshift regions without assuming any cosmological models. It is found that the universe may be opaque between the redshift regions 0.35 0.44, 0.44 0.57 and 0.6-0.73 since the best fit values of cosmic opacity in these regions are positive, while a transparent universe is favored in the redshift region 0.57-0.63. However, in general, a transparent universe is still consistent with observations at the lo confidence level.
基金Supported by National Natural Science Foundation of China(10875129,11075166)
文摘Gravitational field equations in Randers-Finsler space of approximate Berwald type are investigated. A modified Friedmann equation and a new luminosity distance-redshift relation is proposed. A best-fit to the Type Ia supernovae （SNe） observations yields that the Λ in the Λ-CDM model is suppressed to almost zero. This fact indicates that the astronomical observations on the Type Ia SNe can be described well without invoking any form of dark energy. The best-fit age of the universe is given. It is in agreement with the age of our galaxy.
基金Supported by the National Natural Science Fund of China(11603005 and 11775038)
文摘The equation of state(EoS) of dark energy plays an important role in the evolution of the universe and has attracted considerable interest in the recent years. With the progress in observational technique, a precise constraint on the EoS of dark energy can be obtained. In this study, we reconstruct the EoS of dark energy and cosmic expansion using Gaussian processes(GP) from the most up-to-date Pantheon compilation of type Ia supernovae(SNe Ia),which consists of 1048 finely calibrated SNe Ia. The reconstructed EoS of dark energy has a large uncertainty owing to its dependence on the second-order derivative of the construction. Adding the direct measurements of Hubble parameters H(z) as an additional constraint on the first-order derivative can partially reduce the uncertainty;however, it is still not sufficiently precise to distinguish between the evolving and the constant dark energy. Moreover, the results heavily rely on the prior of the Hubble constant H0. The H0 value inferred from SNe+ H(z) without prior is H0= 70.5 ± 0.5 km s^-1 Mpc^-1. Moreover, the matter density ΩM has a non-negligible effect on the reconstruction of dark energy. Therefore, more accurate determinations on H0 and ΩM are required to tightly constrain the EoS of dark energy.
文摘Based on the idea of hypothetical 4-dimensial substance with an inverse population of energy levels, a model of accelerated expansion of the Universe has been developed, which describes Hubble diagrams with great accuracy for type Ia supernovae, quasars and gamma-ray burst sources at the Hubble parameter value of 67.7 km/s/Mpc, coinciding with the value obtained from analysis of inhomogeneities of relic radiation. Calculations at the Hubble parameter value of 73.5 km/s/Mpc, obtained using the ΛCDM model based on the analysis of data on type Ia supernovae and cepheids, differ markedly from the observed data. An explanation of the two values of the Hubble constant is proposed. It is shown that in this model, the magnitude of 13.8 billion years characterizes not the age of the Universe, but the time of propagation of light from those galaxes whose acceleration of removal has a minimal value. Based on the recently discovered curvature of the Universe, estimates are given of the lower limits of its size and lifetime, which turned out to be at least 270 billon years. The probability of transition from the excited state to the underlying energy levels of a hypothetical 4-dimensial substance, as well as the low of increasing energy density as a result of transitions to the underlying levels of this substance, is determined.
基金the National Natural Science Fund of China(12147102,12275034)the Fundamental Research Funds for the Central Universities of China(2023CDJXY-048)。
文摘We investigate the possible anisotropy of the universe using data on the most up-to-date type Ia supernovae,i.e.,the Pantheon+compilation.We fit the full Pantheon+data with the dipole-modulated ΛCDM model and find that the data are well consistent with a null dipole.We further divide the full sample into several subsamples with different high-redshift cutoffs zc.It is shown that the dipole appears at the 2σ confidence level only if z_(c)≤0.1,and in this redshift region,the dipole is very stable,almost independent of the specific value of zc.For z_(c)=0.1,the dipole amplitude is D=1.0_(-0.4^(+0.4))×10^(-3),pointing toward(l,b)=(334.5°_(-21.6°)^(+25.7°),16.0°_(-16.8°)^(+27.1°)),which is approximately 65°away from the CMB dipole.This implies that the full Pantheon+sample is consistent with a large-scale isotropic universe,but the low-redshift anisotropy could not be purely explained by the peculiar motion of the local universe.
文摘Realistic FLRW cosmic coasting models which contain matter now appear to be a reasonable alternative in explaining the accumulated Supernova Cosmology Project data since 1998. In sharp contrast to the unrealistic original classic Milne universe, which was entirely devoid of matter, these modified Milne-type models containing matter, often referred to as realistic linear Rh = ct models, have rapidly become the primary competition with standard cosmology. This paper compares the expected relative luminosity distances and relative angular diameter distances for given magnitudes of redshift within these two competing models. A simple ratio formula is derived, which explains how expected luminosity distances and angular diameter distances for given magnitudes of redshift within a realistic Milne-type cosmic expansion could create the illusion (for standard model proponents) of cosmic acceleration where none exists.
基金supported by the National Natural Science Foundation of China under Grant No.11405024the Fundamental Research Funds for the Central Universities under Grant No.16lgpy50。
文摘In this work,we explore the cosmological consequences of the latest Type Ia supernova(SN Ia)dataset,Pantheon,by adopting the wCDM model.The Pantheon dataset currently contains the largest number of SN Ia samples,which contains 1048 supernovae on the redshift range 0<z<2.3.Here we take into account three kinds of SN Ia statistics techniques,including:(1)magnitude statistics(MS),which is the traditional SN Ia statistics technique;(2)flux statistics(FS),which is based on the flux-averaging(FA)method;and(3)improved flux statistics(IFS),which combines the advantages of MS and FS.It should be mentioned that the IFS technique needs to scan the(zcut,Δz)parameters plane,where zcut andΔz are redshift cut-off and redshift interval of FA,respectively.The results are as follows.(1)Using the SN dataset only,the best FA recipe for IFS is(zcut,Δz)=(0.1,0.08);(2)comparing to the old SN dataset,JLA,adopting the Pantheon dataset can reduce the 2σerror bars of equation of state w by 38%,47%and 53%for MS,FS and IFS,respectively;(3)FS gives closer results to other observations,such as Baryon acoustic oscillations and cosmic microwave background;(4)compared with FS and IFS,MS more favors a Universe that will end in a‘big rip’.
基金supported by the National Natural Science Foundation of China(Grant Nos.11405024 and 11175042)the Fundamental Research Fundsfor the Central Universities(Grant Nos.N130305007 and N120505003)
文摘Previous studies have shown that for the Supernova Legacy Survey three-year(SNLS3)data there is strong evidence for the redshiftevolution of color-luminosity parameterβof type Ia supernovae(SN Ia).In this paper,we explore the effects of varyingβon the cosmological constraints of holographic dark energy(HDE)model.In addition to the SNLS3 data,we also use Planck distance prior data of cosmic microwave background(CMB),as well as galaxy clustering(GC)data extracted from Sloan Digital Sky Survey(SDSS)data release 7 and Baryon Oscillation Spectroscopic Survey(BOSS).We find that,for the both cases of using SN data alone and using SN+CMB+GC data,involving an additional parameter ofβcan reduceχ2by～36;this shows thatβdeviates from a constant at 6σconfidence levels.Adopting SN+CMB+GC data,we find that compared to the constantβcase,varyingβyields a larger fractional matter density-m0and a smaller reduced Hubble constant h;moreover,varyingβsignificantly increases the value of HDE model parameter c,leading to c≈0.8,consistent with the constraint results obtained before Planck.These results indicate that the evolution ofβshould be taken into account seriously in the cosmological fits.In addition,we find that relative to the differences between the constantβand varyingβ(z)cases,the effects of different light-curve fitters on parameter estimation are very small.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11175042,11405024the Fundamental Research Funds for the Central Universities under Grant Nos.N120505003 and N130305007
文摘It has been found that, for the Supernova Legacy Survey three-year(SNLS3) data, there is strong evidence for the redshift-evolution of color-luminosity parameter β. In previous studies, only dark energy(DE) models are used to explore the effects of a time-varying β on parameter estimation. In this paper, we extend the discussions to the case of modified gravity(MG), by considering Dvali–Gabadadze–Porrati(DGP) model, power-law type f(T) model and exponential type f(T) model. In addition to the SNLS3 data, we also use the latest Planck distance priors data,the galaxy clustering(GC) data extracted from Sloan Digital Sky Survey(SDSS) data release 7(DR7) and Baryon Oscillation Spectroscopic Survey(BOSS), as well as the direct measurement of Hubble constant H0 from the Hubble Space Telescope(HST) observation. We find that, for both cases of using the supernova(SN) data alone and using the combination of all data, adding a parameter of β can reduce χ2by ～ 36 for all the MG models, showing that a constantβ is ruled out at 6σ confidence level(CL). Moreover, we find that a time-varying β always yields a larger fractional matter density Ωm0and a smaller reduced Hubble constant h; in addition, it significantly changes the shapes of 1σ and2σ confidence regions of various MG models, and thus corrects systematic bias for the parameter estimation. These conclusions are consistent with the results of DE models, showing that β's evolution is completely independent of the cosmological models in the background. Therefore, our work highlights the importance of considering the evolution of βin the cosmology-fits.
