In this study,we investigate the potential of mark-weighted angular correlation functions,which integrateβ-cosmic-web classification with angular correlation function analysis to improve cosmological constraints.Usin...In this study,we investigate the potential of mark-weighted angular correlation functions,which integrateβ-cosmic-web classification with angular correlation function analysis to improve cosmological constraints.Using SDSS DR12 CMASS-NGC galaxies and mock catalogs withΩ_(m)varying from 0.25 to 0.40,we assess the discriminative power of different statistics via the average improvement in chi-squared,ΔX^(2),across six redshift bins.This metric quantifies how effectively each statistic distinguishes between different cosmological models.Incorporating cosmic-web weights leads to substantial improvements.Using statistics weighted by the mean neighbor distance(Dnei)increasesΔX^(2)by approximately 40%–130%,while applying inverse mean neighbor distance weighting(1/Dnei)yields even larger gains,boostingΔX^(2)by a factor of 2–3 compared to traditional unweighted angular statistics.These enhancements are consistent with previous 3D clustering results,demonstrating the superior sensitivity of theβ-weighted approaches.Our method,based on thin redshift slices,is particularly suitable for slitless surveys(e.g.,Euclid,CSST)where redshift uncertainties limit 3D analyses.This study also offers a framework for applying marked statistics to 2D angular clustering.展开更多
In this work,we investigate a joint fitting approach based on theoretical models of power spectra associated with density-field reconstruction.Specifically,we consider the matter auto-power spectra before and after ba...In this work,we investigate a joint fitting approach based on theoretical models of power spectra associated with density-field reconstruction.Specifically,we consider the matter auto-power spectra before and after baryon acoustic oscillations(BAO)reconstruction,as well as the cross-power spectrum between the pre-and post-reconstructed density fields.We present redshift-space models for these three power spectra at the one-loop level within the framework of standard perturbation theory,and perform a joint analysis using three types of power spectra,and quantify their impact on parameter constraints.When restricting the analysis to wavenumbers k≤0.2 h Mpc^(−1)and adopting a smoothing scale of R_(s)=15 h^(−1)Mpc,we find that incorporating all three power spectra improves parameter constraints by approximately 11%–16%compared to using only the post-reconstruction power spectrum,with the Figure of Merit increasing by 10.5%.These results highlight the advantages of leveraging multiple power spectra in BAO reconstruction,ultimately enabling more precise cosmological parameter estimation.展开更多
A theory of（4＋1）-dimensional gravity has been developed on the basis of which equivalent to the theory of general relativity by teleparallel.The fundamental gravitational field variables are the 5-dimensional（5D）...A theory of（4＋1）-dimensional gravity has been developed on the basis of which equivalent to the theory of general relativity by teleparallel.The fundamental gravitational field variables are the 5-dimensional（5D） vector fields（pentad）,defined globally on a manifold M,and gravity is attributed to the torsion.The Lagrangian density is quadratic in the torsion tensor.We then apply the field equations to two different homogenous and isotropic geometric structures which give the same line element,i.e.,FRW in five dimensions.The cosmological parameters are calculated and some cosmological problems are discussed.展开更多
<p align="justify"> <span style="font-family:Verdana;"></span><span style="font-family:Verdana;"></span>It is well known that Einstein published in June 1905...<p align="justify"> <span style="font-family:Verdana;"></span><span style="font-family:Verdana;"></span>It is well known that Einstein published in June 1905 his theory of Special Relativity (SR) without entirely based on space-time Lorentz Transformation (LT) with invariance of Light Velocity. It is much less known that Poincaré published, practically at the same time, a SR also based entirely on LT with also an invariant velocity. However, according to Poincaré, the invariant is not only that of light wave but also that of Gravific Wave in Ether. Poincaré’s Gravific ether exerts also a Gravific pressure, in the same paper, on <i>charged </i>(e) Electron (a “Hole in Ether” according to Poincaré). There are thus two SR: That of Einstein (ESR), without ether and without gravitation, and that of Poincaré (PSR), with Electro-Gravific-Ether. The crucial question arises then: Does “SPECIAL” Poincaré’s (e)-G field fall in the framework of Einstein’s GENERAL Relativity? Our answer is positive. On the basis of Einstein’s equation of gravitation (1917) with Minkowskian Metric (MM) and Zero Constant Cosmological (CC) we rediscover usual Static Vacuum (without <i>charge e </i>of electron). On the other hand with MM and <i>Non-Zero </i>CC, we discover the gravific field of a Cosmological Black Hole (CBH) with density of dark energy compatible with expanding vacuum. Hawking’s Stellar Black Hole (SBH) emits outgoing Black Radiation, whilst Poincaré’s CBH emits (at time zero) incoming Black Radiation. We show that Poincaré’s G-electron involves a (quantum) GRAVITON (on the model of Einstein’s quantum photon) underlying a de Broglie’s G-Wave. There is therefore a Gackground Cosmological model in Poincaré’s basic paper which predicts a density and a temperature of CBR very close to the observed (COBE) values. </p>展开更多
By means of the dimensional analysis a spherically simmetric universe with a mass M = c<sup>3</sup>/(2HG) and radius equal to c/H is considered, where H is the Hubble constant, c the speed of light and G t...By means of the dimensional analysis a spherically simmetric universe with a mass M = c<sup>3</sup>/(2HG) and radius equal to c/H is considered, where H is the Hubble constant, c the speed of light and G the Newton gravitational constant. The density corresponding to this mass is equal to the critical density ρ<sub>cr </sub>= 3H<sup>2</sup>/(8πG). This universe evolves according to a Bondi-Gold-Hoyle scenario, with continuous creation of matter at a rate such to maintain, during the expansion, the density always critical density. Using the Margolus-Levitin theorem and the Landauer’s principle, an entropy is associated with this universe, obtaining a formula having the same structure as the Bekenstein-Hawking formula of the entropy of a black hole. Furthermore, a time-dependent cosmological constant Λ, function of the Hubble constant and the speed of light, is proposed.展开更多
The dependence of chaos on two parameters of the cosmological constant and the self-interacting coefficient in the imaginary phase space for a closed Friedman- Robertson-Walker （FRW） universe with a conformally coup...The dependence of chaos on two parameters of the cosmological constant and the self-interacting coefficient in the imaginary phase space for a closed Friedman- Robertson-Walker （FRW） universe with a conformally coupled scalar field, as the full understanding of the dependence in real phase space, is investigated numerically. It is found that Poincar6 plots for the two parameters less than 1 are almost the same as those in the absence of the cosmological constant and self-interacting terms. For energies below the energy threshold of 0.5 for the imaginary problem in which there are no cosmological constant and self-interacting terms, an abrupt transition to chaos occurs when at least one of the two parameters is 1. However, the strength of the chaos does not increase for energies larger than the threshold. For other situations of the two parameters larger than 1, chaos is weaker, and even disappears as the two parameters increase.展开更多
The importance of cosmological constant for the cosmological models is given. The variations of the cosmological model for parameters and were discussed respectively. Near , the cosmological model is unstable with t...The importance of cosmological constant for the cosmological models is given. The variations of the cosmological model for parameters and were discussed respectively. Near , the cosmological model is unstable with the change of , and near , the cosmological model is unstable with the change of . So when we consider the stable cosmological model, we must consider the nonzero cosmological constant.展开更多
We are looking at comparison of two action integrals and we identify the Lagrangian multiplier as setting up a constraint equation (on cosmological expansion). This is a direct result of the fourth equation of our man...We are looking at comparison of two action integrals and we identify the Lagrangian multiplier as setting up a constraint equation (on cosmological expansion). This is a direct result of the fourth equation of our manuscript which unconventionally compares the action integral of General relativity with the second derived action integral, which then permits Equation (5), which is a bound on the Cosmological constant. What we have done is to replace the Hamber Quantum gravity reference-based action integral with a result from John Klauder’s “Enhanced Quantization”. In doing so, with Padamabhan’s treatment of the inflaton, we then initiate an explicit bound upon the cosmological constant. The other approximation is to use the inflaton results and conflate them with John Klauder’s Action principle for a way, if we have the idea of a potential well, generalized by Klauder, with a wall of space time in the Pre Planckian-regime to ask what bounds the Cosmological constant prior to inflation, and to get an upper bound on the mass of a graviton. We conclude with a redo of a multiverse version of the Penrose cyclic conformal cosmology. Our objective is to show how a value of the rest mass of the heavy graviton is invariant from cycle to cycle. All this is possible due to Equation (4). And we compare all these with results of Reference [1] in the conclusion, while showing its relevance to early universe production of black holes, and the volume of space producing 100 black holes of value about 10^2 times Planck Mass. Initially evaluated in a space-time of about 10^3 Planck length, in spherical length, we assume a starting entropy of about 1000 initially.展开更多
Gravitational wave(GW) signals from compact binary coalescences can be used as standard sirens to constrain cosmological parameters if their redshift can be measured independently by electromagnetic signals.However,me...Gravitational wave(GW) signals from compact binary coalescences can be used as standard sirens to constrain cosmological parameters if their redshift can be measured independently by electromagnetic signals.However,mergers of stellar binary black holes(BBHs) may not have electromagnetic counterparts and thus have no direct redshift measurements.These dark sirens may be still used to statistically constrain cosmological parameters by combining their GW measured luminosity distances and localization with deep redshift surveys of galaxies around it.We investigate this dark siren method to constrain cosmological parameters in detail by using mock BBH and galaxy samples.We find that the Hubble constant can be constrained well with an accuracy■ 1% with a few tens or more of BBH mergers at redshift up to 1 if GW observations can provide accurate estimates of their luminosity distance(with relative error of■ 0.01) and localization(■ 0.1 deg^(2)),though the constraint may be significantly biased if the luminosity distance and localization errors are larger.We also introduce a simple method to correct this bias and find it is valid when the luminosity distance and localization errors are modestly large.We further generate mock BBH samples,according to current constraints on BBH merger rate and the distributions of BBH properties,and find that the Deci-hertz Observatory(DO) in a half year observation period may detect about one hundred BBHs with signal-to-noise ratio■■30,relative luminosity distance error■ 0.02 and localization error ■0.01 deg^(2).By applying the dark standard siren method,we find that the Hubble constant can be constrained to the~0.1%-1% level using these DO BBHs,an accuracy comparable to the constraints obtained by using electromagnetic observations in the near future,thus it may provide insight into the Hubble tension.We also demonstrate that the constraint on the Hubble constant applying this dark siren method is robust and does not depend on the choice of the prior for the properties of BBH host galaxies.展开更多
Some cylindrically symmetric inhomogeneous viscous fluid string cosmological models with magnetic field and cosmological term A varying with time are investigated. To get the deterministic solution, it has been assume...Some cylindrically symmetric inhomogeneous viscous fluid string cosmological models with magnetic field and cosmological term A varying with time are investigated. To get the deterministic solution, it has been assumed that the expansion （θ） in the model is proportional to the eigen value σ^11 of the shear tensor σ^ij. The value of cosmological constant for the model is found to be small and positive, which is supported by the results from recent supernovae Ia observations. The effect of bulk viscosity is to produce a change in perfect fluid and hence exhibits essential influence on the character of the solution. The physical and geometric properties of the models are also discussed in presence and absence of magnetic field.展开更多
Recently, Cai and Su [Phys. Rev. D 81 （2010） 103514] found that the sign of interaction Q in＇the dark sector changed in the approximate redshift range of 0.45 ≤ z ≤0.9, by using a modeMndependent method to deal w...Recently, Cai and Su [Phys. Rev. D 81 （2010） 103514] found that the sign of interaction Q in＇the dark sector changed in the approximate redshift range of 0.45 ≤ z ≤0.9, by using a modeMndependent method to deal with the observational data. In fact, this result raises a remarkable problem, since most of the familiar interactions cannot change their signs in the whole cosmic history. Motivated by the work of Cai and Su, we have proposed a new type of interaction in a previous work [H. Wei, Nucl. Phys. B 845 （2011） 381]. The key ingredient is the deceleration parameter q in the interaction Q, and hence the interaction Q can change its sign when our universe changes from deceleration （q 〉0） to acceleration （q 〈 0）. In the present work, we consider the cosmologicai constraints on this new type of sign-changeable interactions, by using the latest observational data. We find that the cosmological constraints on the model parameters are fairly tight. In particular, the key parameter β can be constrained to a narrow range.展开更多
The locally rotationally symmetric Bianchi-type II string cosmological models with bulk viscosity are obtained, where an equation of state, , and a relation between metric potentials, , are adopted. The physical featu...The locally rotationally symmetric Bianchi-type II string cosmological models with bulk viscosity are obtained, where an equation of state, , and a relation between metric potentials, , are adopted. The physical features of the models are also discussed. In special cases the model reduces to the string models without viscosity that was previously given in the literatures.展开更多
We constrain cosmological parameters using only Hubble parameter data and quantify the impact of future Hubble parameter measurements on parameter estimation for the most typical dark energy models. We first constrain...We constrain cosmological parameters using only Hubble parameter data and quantify the impact of future Hubble parameter measurements on parameter estimation for the most typical dark energy models. We first constrain cosmological parameters using 52 current Hubble parameter data including the Hubble constant measurement from the Hubble Space Telescope. Then we simulate the baryon acoustic oscillation signals from WFIRST(Wide-Field Infrared Survey Telescope) covering the redshift range of z ∈ [0.5, 2] and the redshift drift data from E-ELT(European Extremely Large Telescope) in the redshift range of z ∈ [2, 5]. It is shown that solely using the current Hubble parameter data could give fairly good constraints on cosmological parameters. Compared to the current Hubble parameter data, with the WFIRST observation the H(z) constraints on dark energy would be improved slightly, while with the E-ELT observation the H(z) constraints on dark energy is enormously improved.展开更多
Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clu...Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clusters lie between 0.1 and 0.6,and the redshift range of their arcs is from 0.4 to 4.9.These clusters are selected carefully from strong gravitational lensing systems which have both X-ray satellite observations and optical giant luminous arcs with known redshifts.Giant arcs usually appear in the central region of clusters,where mass can be traced with luminosity quite well.Based on gravitational lensing theory and a cluster mass distribution model,we can derive a ratio using two angular diameter distances.One is the distance between lensing sources and the other is that between the deflector and the source. Since angular diameter distance relies heavily on cosmological geometry,we can use these ratios to constrain cosmological models.Moreover,X-ray gas fractions of galaxy clusters can also be a cosmological probe.Because there are a dozen parameters to be fitted,we introduce a new analytic algorithm,Powell＇s UOBYQA（Unconstrained Optimization By Quadratic Approximation） ,to accelerate our calculation.Our result demonstrates that this algorithm is an effective fitting method for such a continuous multi-parameter constraint.We find an interesting fact that these two approaches are separately sensitive toΩΛandΩM.By combining them,we can get reasonable fitting values of basic cosmological parameters：ΩM=0.26 ＋0.04 -0.04,andΩΛ=0.82 ＋0.14 -0.16.展开更多
Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for a Robertson-Walker universe by assuming the cosmological term to be proportional t...Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for a Robertson-Walker universe by assuming the cosmological term to be proportional to R-m（R is a scale factor and m is a constant）.A variety of solutions is presented.The physical significance of the cosmological models has also been discussed.展开更多
Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for the Bianchi type-I universe by assuming that the cosmological term is proportional...Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for the Bianchi type-I universe by assuming that the cosmological term is proportional to R-m （R is a scale factor and m is a constant）.A variety of solutions are presented.The physical significance of the respective cosmological models are also discussed.展开更多
We explore the problems of degeneracy and discreteness in the standard cosmological model（ΛCDM）. We use the Observational Hubble Data（OHD） and the type Ia supernovae（SNe Ia） data to study this issue. In order t...We explore the problems of degeneracy and discreteness in the standard cosmological model（ΛCDM）. We use the Observational Hubble Data（OHD） and the type Ia supernovae（SNe Ia） data to study this issue. In order to describe the discreteness in fitting of data, we define a factor G to test the influence from each single data point and analyze the goodness of G. Our results indicate that a higher absolute value of G shows a better capability of distinguishing models, which means the parameters are restricted into smaller confidence intervals with a larger figure of merit evaluation. Consequently, we claim that the factor G is an effective way of model differentiation when using different models to fit the observational data.展开更多
Using the Klauder enhanced quantization as a way to specify the cosmological constant as a baseline for the mass of a graviton, we eventually come up and then we will go to the Starobinsky potential as a replacement f...Using the Klauder enhanced quantization as a way to specify the cosmological constant as a baseline for the mass of a graviton, we eventually come up and then we will go to the Starobinsky potential as a replacement for the term N used in Equation (3) and Equation (4). From there we will read in a way to describe conditions allowing for where the cosmological constant may be set. The idea also is to describe a regime of space-time where the initial perturbation/start to inflation actually occurred, as is alluded to in the final part of the document.展开更多
This article poses the question of a minimum cosmological constant, i.e. vacuum energy at the start of the cosmological evolution from a near singularity. We pose this comparing formalism as given by Berry (1976) as t...This article poses the question of a minimum cosmological constant, i.e. vacuum energy at the start of the cosmological evolution from a near singularity. We pose this comparing formalism as given by Berry (1976) as to a small time length, and compare that in its entirety to compare this value given by Berry (1976) with a minimum time length at the start of cosmological space-time evolution. Using the methodology of Zeldovich (1972) as to a problem with electron-positron pair production we also propose another upper bound to the problem of minimum time length which may be accessible to experimental inquiry. This then makes the problem of minimum time length a way of specifying a magnetic field dependence of the cosmological constant, which has major implications to answering if quintessence, i.e. a changing cosmological vacuum energy, or a constant for the “cosmological constant” problem. Our answer is an initial value for the cosmological vacuum energy 10<sup>10</sup> - 10<sup>20</sup> times greater than today which suggests either Quintessence, or if still a constant, a much better value for this parameter than what is suggested by traditional field theory methods. In closing we review how our construct supports work done by Corda, as to early universe models and what the implications are, as to the choices we have made.展开更多
We reduplicate the Book “Dark Energy” by M. Li, X-D. Li, and Y. Wang, given zero-point energy calculation with an unexpected “length” added to the “width” of a graviton wave just prior to specifying the creation...We reduplicate the Book “Dark Energy” by M. Li, X-D. Li, and Y. Wang, given zero-point energy calculation with an unexpected “length” added to the “width” of a graviton wave just prior to specifying the creation of “gravitons”, while using Karen Freeze’s criteria as to the breakup of primordial black holes to give radiation era contributions to GW generation. The GW generation will be when there is sufficient early universe density so as to break apart Relic Black holes of the order of Planck mass (10<sup>15</sup> grams) which is about when the mass of relic black holes is created, 10<sup>-27</sup> or so seconds after expansion starts. Needles to state a key result will be in the initial potential V calculated, in terms of other input variables.展开更多
基金supported by the Ministry of Science and Technology of China(2020SKA0110401,2020SKA0110402 and 2020SKA0110100)the National Key Research and Development Program of China(2018YFA0404504,2018YFA0404601 and 2020YFC2201600)+2 种基金the National Natural Science Foundation of China(12373005,11890691,12205388,12220101003 and 12473097)the China Manned Space Project with numbers CMS-CSST-2021(A02,A03,B01)Guangdong Basic and Applied Basic Research Foundation(2024A1515012309)。
文摘In this study,we investigate the potential of mark-weighted angular correlation functions,which integrateβ-cosmic-web classification with angular correlation function analysis to improve cosmological constraints.Using SDSS DR12 CMASS-NGC galaxies and mock catalogs withΩ_(m)varying from 0.25 to 0.40,we assess the discriminative power of different statistics via the average improvement in chi-squared,ΔX^(2),across six redshift bins.This metric quantifies how effectively each statistic distinguishes between different cosmological models.Incorporating cosmic-web weights leads to substantial improvements.Using statistics weighted by the mean neighbor distance(Dnei)increasesΔX^(2)by approximately 40%–130%,while applying inverse mean neighbor distance weighting(1/Dnei)yields even larger gains,boostingΔX^(2)by a factor of 2–3 compared to traditional unweighted angular statistics.These enhancements are consistent with previous 3D clustering results,demonstrating the superior sensitivity of theβ-weighted approaches.Our method,based on thin redshift slices,is particularly suitable for slitless surveys(e.g.,Euclid,CSST)where redshift uncertainties limit 3D analyses.This study also offers a framework for applying marked statistics to 2D angular clustering.
基金supported by the National Natural Science Foundation of China(NSFC,Grant No.12525301)supported by the Science and Technology Facilities Council(STFC)under Grant ST/W001225/1+6 种基金supported by JSPS KAKENHI grant Nos.JP22H00130 and JP20H05855further acknowledges support form the National Key R&D Program of China No.(2022YFF0503404,2023YFA1607800,2023YFA1607803)the National Natural Science Foundation of China(NSFC,Grant Nos.12273048 and 12422301)the CAS Project for Young Scientists in Basic Research(No.YSBR-092)support from the CAS Project for Young Scientists in Basic Research(No.YSBR092)the China Manned Space Projectthe New Cornerstone Science Foundation through the XPLORER Prize.
文摘In this work,we investigate a joint fitting approach based on theoretical models of power spectra associated with density-field reconstruction.Specifically,we consider the matter auto-power spectra before and after baryon acoustic oscillations(BAO)reconstruction,as well as the cross-power spectrum between the pre-and post-reconstructed density fields.We present redshift-space models for these three power spectra at the one-loop level within the framework of standard perturbation theory,and perform a joint analysis using three types of power spectra,and quantify their impact on parameter constraints.When restricting the analysis to wavenumbers k≤0.2 h Mpc^(−1)and adopting a smoothing scale of R_(s)=15 h^(−1)Mpc,we find that incorporating all three power spectra improves parameter constraints by approximately 11%–16%compared to using only the post-reconstruction power spectrum,with the Figure of Merit increasing by 10.5%.These results highlight the advantages of leveraging multiple power spectra in BAO reconstruction,ultimately enabling more precise cosmological parameter estimation.
文摘A theory of（4＋1）-dimensional gravity has been developed on the basis of which equivalent to the theory of general relativity by teleparallel.The fundamental gravitational field variables are the 5-dimensional（5D） vector fields（pentad）,defined globally on a manifold M,and gravity is attributed to the torsion.The Lagrangian density is quadratic in the torsion tensor.We then apply the field equations to two different homogenous and isotropic geometric structures which give the same line element,i.e.,FRW in five dimensions.The cosmological parameters are calculated and some cosmological problems are discussed.
文摘<p align="justify"> <span style="font-family:Verdana;"></span><span style="font-family:Verdana;"></span>It is well known that Einstein published in June 1905 his theory of Special Relativity (SR) without entirely based on space-time Lorentz Transformation (LT) with invariance of Light Velocity. It is much less known that Poincaré published, practically at the same time, a SR also based entirely on LT with also an invariant velocity. However, according to Poincaré, the invariant is not only that of light wave but also that of Gravific Wave in Ether. Poincaré’s Gravific ether exerts also a Gravific pressure, in the same paper, on <i>charged </i>(e) Electron (a “Hole in Ether” according to Poincaré). There are thus two SR: That of Einstein (ESR), without ether and without gravitation, and that of Poincaré (PSR), with Electro-Gravific-Ether. The crucial question arises then: Does “SPECIAL” Poincaré’s (e)-G field fall in the framework of Einstein’s GENERAL Relativity? Our answer is positive. On the basis of Einstein’s equation of gravitation (1917) with Minkowskian Metric (MM) and Zero Constant Cosmological (CC) we rediscover usual Static Vacuum (without <i>charge e </i>of electron). On the other hand with MM and <i>Non-Zero </i>CC, we discover the gravific field of a Cosmological Black Hole (CBH) with density of dark energy compatible with expanding vacuum. Hawking’s Stellar Black Hole (SBH) emits outgoing Black Radiation, whilst Poincaré’s CBH emits (at time zero) incoming Black Radiation. We show that Poincaré’s G-electron involves a (quantum) GRAVITON (on the model of Einstein’s quantum photon) underlying a de Broglie’s G-Wave. There is therefore a Gackground Cosmological model in Poincaré’s basic paper which predicts a density and a temperature of CBR very close to the observed (COBE) values. </p>
文摘By means of the dimensional analysis a spherically simmetric universe with a mass M = c<sup>3</sup>/(2HG) and radius equal to c/H is considered, where H is the Hubble constant, c the speed of light and G the Newton gravitational constant. The density corresponding to this mass is equal to the critical density ρ<sub>cr </sub>= 3H<sup>2</sup>/(8πG). This universe evolves according to a Bondi-Gold-Hoyle scenario, with continuous creation of matter at a rate such to maintain, during the expansion, the density always critical density. Using the Margolus-Levitin theorem and the Landauer’s principle, an entropy is associated with this universe, obtaining a formula having the same structure as the Bekenstein-Hawking formula of the entropy of a black hole. Furthermore, a time-dependent cosmological constant Λ, function of the Hubble constant and the speed of light, is proposed.
基金supported by the Natural Science Foundation of China (Grant No. 10873007)supported by the Science Foundation of Jiangxi Education Bureau (GJJ09072)the Program for Innovative Research Teams of Nanchang University
文摘The dependence of chaos on two parameters of the cosmological constant and the self-interacting coefficient in the imaginary phase space for a closed Friedman- Robertson-Walker （FRW） universe with a conformally coupled scalar field, as the full understanding of the dependence in real phase space, is investigated numerically. It is found that Poincar6 plots for the two parameters less than 1 are almost the same as those in the absence of the cosmological constant and self-interacting terms. For energies below the energy threshold of 0.5 for the imaginary problem in which there are no cosmological constant and self-interacting terms, an abrupt transition to chaos occurs when at least one of the two parameters is 1. However, the strength of the chaos does not increase for energies larger than the threshold. For other situations of the two parameters larger than 1, chaos is weaker, and even disappears as the two parameters increase.
文摘The importance of cosmological constant for the cosmological models is given. The variations of the cosmological model for parameters and were discussed respectively. Near , the cosmological model is unstable with the change of , and near , the cosmological model is unstable with the change of . So when we consider the stable cosmological model, we must consider the nonzero cosmological constant.
文摘We are looking at comparison of two action integrals and we identify the Lagrangian multiplier as setting up a constraint equation (on cosmological expansion). This is a direct result of the fourth equation of our manuscript which unconventionally compares the action integral of General relativity with the second derived action integral, which then permits Equation (5), which is a bound on the Cosmological constant. What we have done is to replace the Hamber Quantum gravity reference-based action integral with a result from John Klauder’s “Enhanced Quantization”. In doing so, with Padamabhan’s treatment of the inflaton, we then initiate an explicit bound upon the cosmological constant. The other approximation is to use the inflaton results and conflate them with John Klauder’s Action principle for a way, if we have the idea of a potential well, generalized by Klauder, with a wall of space time in the Pre Planckian-regime to ask what bounds the Cosmological constant prior to inflation, and to get an upper bound on the mass of a graviton. We conclude with a redo of a multiverse version of the Penrose cyclic conformal cosmology. Our objective is to show how a value of the rest mass of the heavy graviton is invariant from cycle to cycle. All this is possible due to Equation (4). And we compare all these with results of Reference [1] in the conclusion, while showing its relevance to early universe production of black holes, and the volume of space producing 100 black holes of value about 10^2 times Planck Mass. Initially evaluated in a space-time of about 10^3 Planck length, in spherical length, we assume a starting entropy of about 1000 initially.
基金partly supported by the National Key Program for Science and Technology Research and Development(Grant Nos. 2020YFC2201400, 2020SKA0120102 and 2016YFA0400704)the National Natural Science Foundation of China (Grant No. 11690024)the Strategic Priority Program of the Chinese Academy of Sciences (Grant XDB23040100)。
文摘Gravitational wave(GW) signals from compact binary coalescences can be used as standard sirens to constrain cosmological parameters if their redshift can be measured independently by electromagnetic signals.However,mergers of stellar binary black holes(BBHs) may not have electromagnetic counterparts and thus have no direct redshift measurements.These dark sirens may be still used to statistically constrain cosmological parameters by combining their GW measured luminosity distances and localization with deep redshift surveys of galaxies around it.We investigate this dark siren method to constrain cosmological parameters in detail by using mock BBH and galaxy samples.We find that the Hubble constant can be constrained well with an accuracy■ 1% with a few tens or more of BBH mergers at redshift up to 1 if GW observations can provide accurate estimates of their luminosity distance(with relative error of■ 0.01) and localization(■ 0.1 deg^(2)),though the constraint may be significantly biased if the luminosity distance and localization errors are larger.We also introduce a simple method to correct this bias and find it is valid when the luminosity distance and localization errors are modestly large.We further generate mock BBH samples,according to current constraints on BBH merger rate and the distributions of BBH properties,and find that the Deci-hertz Observatory(DO) in a half year observation period may detect about one hundred BBHs with signal-to-noise ratio■■30,relative luminosity distance error■ 0.02 and localization error ■0.01 deg^(2).By applying the dark standard siren method,we find that the Hubble constant can be constrained to the~0.1%-1% level using these DO BBHs,an accuracy comparable to the constraints obtained by using electromagnetic observations in the near future,thus it may provide insight into the Hubble tension.We also demonstrate that the constraint on the Hubble constant applying this dark siren method is robust and does not depend on the choice of the prior for the properties of BBH host galaxies.
文摘Some cylindrically symmetric inhomogeneous viscous fluid string cosmological models with magnetic field and cosmological term A varying with time are investigated. To get the deterministic solution, it has been assumed that the expansion （θ） in the model is proportional to the eigen value σ^11 of the shear tensor σ^ij. The value of cosmological constant for the model is found to be small and positive, which is supported by the results from recent supernovae Ia observations. The effect of bulk viscosity is to produce a change in perfect fluid and hence exhibits essential influence on the character of the solution. The physical and geometric properties of the models are also discussed in presence and absence of magnetic field.
基金Supported in part by National Natural Science Foundation of China under Grant No. 10905005the Excellent Young Scholars Research Fund of Beijing Institute of Technologythe Fundamental Research Fund of Beijing Institute of Technology
文摘Recently, Cai and Su [Phys. Rev. D 81 （2010） 103514] found that the sign of interaction Q in＇the dark sector changed in the approximate redshift range of 0.45 ≤ z ≤0.9, by using a modeMndependent method to deal with the observational data. In fact, this result raises a remarkable problem, since most of the familiar interactions cannot change their signs in the whole cosmic history. Motivated by the work of Cai and Su, we have proposed a new type of interaction in a previous work [H. Wei, Nucl. Phys. B 845 （2011） 381]. The key ingredient is the deceleration parameter q in the interaction Q, and hence the interaction Q can change its sign when our universe changes from deceleration （q 〉0） to acceleration （q 〈 0）. In the present work, we consider the cosmologicai constraints on this new type of sign-changeable interactions, by using the latest observational data. We find that the cosmological constraints on the model parameters are fairly tight. In particular, the key parameter β can be constrained to a narrow range.
文摘The locally rotationally symmetric Bianchi-type II string cosmological models with bulk viscosity are obtained, where an equation of state, , and a relation between metric potentials, , are adopted. The physical features of the models are also discussed. In special cases the model reduces to the string models without viscosity that was previously given in the literatures.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11522540,11690021,11375153,11675145the National Program for Support of Top-Notch Young Professionalsthe 2016 Program for Postdoctoral Fellowship of Zhejiang Province
文摘We constrain cosmological parameters using only Hubble parameter data and quantify the impact of future Hubble parameter measurements on parameter estimation for the most typical dark energy models. We first constrain cosmological parameters using 52 current Hubble parameter data including the Hubble constant measurement from the Hubble Space Telescope. Then we simulate the baryon acoustic oscillation signals from WFIRST(Wide-Field Infrared Survey Telescope) covering the redshift range of z ∈ [0.5, 2] and the redshift drift data from E-ELT(European Extremely Large Telescope) in the redshift range of z ∈ [2, 5]. It is shown that solely using the current Hubble parameter data could give fairly good constraints on cosmological parameters. Compared to the current Hubble parameter data, with the WFIRST observation the H(z) constraints on dark energy would be improved slightly, while with the E-ELT observation the H(z) constraints on dark energy is enormously improved.
基金Supported by the National Natural Science Foundation of Chinasupported by the National Science Foundation of China under the Distinguished Young Scholar Grant 10825313by the Ministry of Science and Technology's National Basic Science Program(Project 973)under grant No.2007CB815401
文摘Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clusters lie between 0.1 and 0.6,and the redshift range of their arcs is from 0.4 to 4.9.These clusters are selected carefully from strong gravitational lensing systems which have both X-ray satellite observations and optical giant luminous arcs with known redshifts.Giant arcs usually appear in the central region of clusters,where mass can be traced with luminosity quite well.Based on gravitational lensing theory and a cluster mass distribution model,we can derive a ratio using two angular diameter distances.One is the distance between lensing sources and the other is that between the deflector and the source. Since angular diameter distance relies heavily on cosmological geometry,we can use these ratios to constrain cosmological models.Moreover,X-ray gas fractions of galaxy clusters can also be a cosmological probe.Because there are a dozen parameters to be fitted,we introduce a new analytic algorithm,Powell＇s UOBYQA（Unconstrained Optimization By Quadratic Approximation） ,to accelerate our calculation.Our result demonstrates that this algorithm is an effective fitting method for such a continuous multi-parameter constraint.We find an interesting fact that these two approaches are separately sensitive toΩΛandΩM.By combining them,we can get reasonable fitting values of basic cosmological parameters：ΩM=0.26 ＋0.04 -0.04,andΩΛ=0.82 ＋0.14 -0.16.
文摘Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for a Robertson-Walker universe by assuming the cosmological term to be proportional to R-m（R is a scale factor and m is a constant）.A variety of solutions is presented.The physical significance of the cosmological models has also been discussed.
文摘Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for the Bianchi type-I universe by assuming that the cosmological term is proportional to R-m （R is a scale factor and m is a constant）.A variety of solutions are presented.The physical significance of the respective cosmological models are also discussed.
基金supported by the National Natural Science Foundation of China(Grant No.11173006)the National Basic Research Program of China(project 973,No.2012CB821804)
文摘We explore the problems of degeneracy and discreteness in the standard cosmological model（ΛCDM）. We use the Observational Hubble Data（OHD） and the type Ia supernovae（SNe Ia） data to study this issue. In order to describe the discreteness in fitting of data, we define a factor G to test the influence from each single data point and analyze the goodness of G. Our results indicate that a higher absolute value of G shows a better capability of distinguishing models, which means the parameters are restricted into smaller confidence intervals with a larger figure of merit evaluation. Consequently, we claim that the factor G is an effective way of model differentiation when using different models to fit the observational data.
文摘Using the Klauder enhanced quantization as a way to specify the cosmological constant as a baseline for the mass of a graviton, we eventually come up and then we will go to the Starobinsky potential as a replacement for the term N used in Equation (3) and Equation (4). From there we will read in a way to describe conditions allowing for where the cosmological constant may be set. The idea also is to describe a regime of space-time where the initial perturbation/start to inflation actually occurred, as is alluded to in the final part of the document.
文摘This article poses the question of a minimum cosmological constant, i.e. vacuum energy at the start of the cosmological evolution from a near singularity. We pose this comparing formalism as given by Berry (1976) as to a small time length, and compare that in its entirety to compare this value given by Berry (1976) with a minimum time length at the start of cosmological space-time evolution. Using the methodology of Zeldovich (1972) as to a problem with electron-positron pair production we also propose another upper bound to the problem of minimum time length which may be accessible to experimental inquiry. This then makes the problem of minimum time length a way of specifying a magnetic field dependence of the cosmological constant, which has major implications to answering if quintessence, i.e. a changing cosmological vacuum energy, or a constant for the “cosmological constant” problem. Our answer is an initial value for the cosmological vacuum energy 10<sup>10</sup> - 10<sup>20</sup> times greater than today which suggests either Quintessence, or if still a constant, a much better value for this parameter than what is suggested by traditional field theory methods. In closing we review how our construct supports work done by Corda, as to early universe models and what the implications are, as to the choices we have made.
文摘We reduplicate the Book “Dark Energy” by M. Li, X-D. Li, and Y. Wang, given zero-point energy calculation with an unexpected “length” added to the “width” of a graviton wave just prior to specifying the creation of “gravitons”, while using Karen Freeze’s criteria as to the breakup of primordial black holes to give radiation era contributions to GW generation. The GW generation will be when there is sufficient early universe density so as to break apart Relic Black holes of the order of Planck mass (10<sup>15</sup> grams) which is about when the mass of relic black holes is created, 10<sup>-27</sup> or so seconds after expansion starts. Needles to state a key result will be in the initial potential V calculated, in terms of other input variables.
