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
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
This paper integrates a quantum conception of the Planck epoch early universe with FSC model formulae and the holographic principle, to offer a reasonable explanation and solution of the cosmological constant problem....This paper integrates a quantum conception of the Planck epoch early universe with FSC model formulae and the holographic principle, to offer a reasonable explanation and solution of the cosmological constant problem. Such a solution does not appear to be achievable in cosmological models which do not integrate black hole formulae with quantum formulae such as the Stephan-Boltzmann law. As demonstrated herein, assuming a constant value of Lambda over the great span of cosmic time appears to have been a mistake. It appears that Einstein’s assumption of a constant, in terms of vacuum energy density, was not only a mistake for a statically-balanced universe, but also a mistake for a dynamically-expanding universe.展开更多
This brief note brings the reader up-to-date with the recent successes of the new Haug-Tatum cosmology model. In particular, the significance of recent proof that the Stefan-Boltzmann law applies to such a model is em...This brief note brings the reader up-to-date with the recent successes of the new Haug-Tatum cosmology model. In particular, the significance of recent proof that the Stefan-Boltzmann law applies to such a model is emphasized and a rationale for this is given. Remarkably, the proposed solutions of this model have incorporated all 580 supernova redshifts in the Union2 database. Therefore, one can usefully apply this thermodynamic law in the form of a continually expanding black-body universe model. To our knowledge, no other cosmological model has achieved such high-precision observational correlation.展开更多
We develop a cosmological model in a physical background scenario of four time and four space dimensions ((4+4)-dimensions or (4+4)-universe). We show that in this framework the (1+3)-universe is deeply connected with...We develop a cosmological model in a physical background scenario of four time and four space dimensions ((4+4)-dimensions or (4+4)-universe). We show that in this framework the (1+3)-universe is deeply connected with the (3+1)-universe. We argue that this means that in the (4+4)-universe there exists a duality relation between the (1+3)-universe and the (3+1)-universe.展开更多
Motivated by the increasing evidence for the need of a geometry that re- sembles Bianchi morphology to explain the observed anisotropy in the WMAP data, we have discussed some features of Bianchi type VI0 universes in...Motivated by the increasing evidence for the need of a geometry that re- sembles Bianchi morphology to explain the observed anisotropy in the WMAP data, we have discussed some features of Bianchi type VI0 universes in the presence of a fluid that has an anisotropic equation of state （EoS） parameter in general relativity. We present two accelerating dark energy （DE） models with an anisotropic fluid in Bianchi type VI0 space-time. To ensure a deterministic solution, we choose the scale factor a（t） = √tnet, which yields a time-dependent deceleration parameter, representing a class of models which generate a transition of the universe from the early decelerating phase to the recent accelerating phase. Under suitable conditions, the anisotropic mod- els approach an isotropic scenario. The EoS for DE co is found to be time-dependent and its existing range for derived models is in good agreement with data from recent observations of type Ia supernovae （SNe Ia） （Knop et al. 2003）, SNe Ia data com- bined with cosmic microwave background （CMB） anisotropy and galaxy clustering statistics （Tegmark et al. 2004a）, as well as the latest combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift SNe Ia and galaxy clustering. For different values of n, we can generate a class of physically viable DE models. The cosmological constant A is found to be a positive decreasing function of time and it approaches a small positive value at late time （i.e. the present epoch）, which is corroborated by results from recent SN Ia observations. We also ob- serve that our solutions are stable. The physical and geometric aspects of both models are also discussed in detail.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
We investigate a two-fluid anisotropic plane symmetric cosmological model with variable gravitational constant G（t） and cosmological term A（t）. In the two-fluid model, one fluid is chosen to be that of the radiati...We investigate a two-fluid anisotropic plane symmetric cosmological model with variable gravitational constant G（t） and cosmological term A（t）. In the two-fluid model, one fluid is chosen to be that of the radiation field modeling the cosmic microwave background and the other one a perfect fluid modeling the material content of the universe. Exact solutions of the field equations are obtained by using a special form for the average scale factor which corresponds to a specific time-varying deceleration parameter. The model obtained presents a cosmological scenario which describes an early acceleration and late-time deceleration. The gravitation constant increases with the cosmic time whereas the cosmological term decreases and asymptotically tends to zero. The physical and kinematical behaviors of the associated fluid parameters are discussed.展开更多
Spatially homogeneous and anisotropic Bianchi type-I cosmological model containing perfect fluid with quadratic equation of state has been diagnosed in general theory of relativity. To obtain a deterministic solution,...Spatially homogeneous and anisotropic Bianchi type-I cosmological model containing perfect fluid with quadratic equation of state has been diagnosed in general theory of relativity. To obtain a deterministic solution, we have used a relation between metric potentials. The exact solution of Einstein’s field equations thus obtained represents an expanding and decelerating universe. The physical and kinematical parameters of the model have also been analyzed with certain constrained between the parameters of the quadratic equation of state.展开更多
We study the evolution of the dark energy parameter within a Bianchi type-I cosmological model filled with barotropic fluid and dark energy. The solutions have been obtained for power law and exponential forms of the ...We study the evolution of the dark energy parameter within a Bianchi type-I cosmological model filled with barotropic fluid and dark energy. The solutions have been obtained for power law and exponential forms of the expansion parameter （they correspond to a constant deceleration parameter in general relativity）. After a long time, the models tend to be isotropic under certain conditions.展开更多
This article explores the dead universe theory as a novel interpretation for the origin and evolution of the universe, suggesting that our cosmos may have originated from the remnants of a preceding universe. This per...This article explores the dead universe theory as a novel interpretation for the origin and evolution of the universe, suggesting that our cosmos may have originated from the remnants of a preceding universe. This perspective challenges the conventional Big Bang theory, particularly concerning dark matter, the expansion of the universe, and the interpretation of phenomena such as gravitational waves.展开更多
Aims: The expansion of the Universe and gravitation are considered different fundamental properties of the cosmos. We explore whether they are connected and propose an equation that links and unifies them. This equati...Aims: The expansion of the Universe and gravitation are considered different fundamental properties of the cosmos. We explore whether they are connected and propose an equation that links and unifies them. This equation describes the expansion of space as related to the mass of matter in that space. An expanding frame of reference, defined as expanding at the same rate, is the natural frame for an observer since the observer is part of the Universe and expands with it. In this frame, the expansion of the Universe by itself accounts for phenomena previously ascribed to gravitation. Gravity is fictitious and unnecessary. Here, we show that universal expansion naturally manifests as “gravity”. Methods: A theory is presented that postulates a natural expansion of the observer’s frame of reference due to matter and a generalized universal principle of equivalence of acceleration and gravitation that extends to any frame. It is consistent with both the general theory of relativity and our knowledge about the expansion of the Universe. Results: We tested the theory positively by applying its equation to global and local scales of the Universe with available data. It is applied to a Universe of homogeneous mass and discrete two and three-body systems and other phenomena hitherto thought to be unrelated. The results show that the proposed equation is valid at any scale. The fundamental nature of the Universe, from which gravity and other properties are derived, is its expansion.展开更多
Using a rigorous mathematical approach, we demonstrate how the Cosmic Microwave Background (CMB) temperature could simply be a form of geometric mean temperature between the minimum time-dependent Hawking Hubble tempe...Using a rigorous mathematical approach, we demonstrate how the Cosmic Microwave Background (CMB) temperature could simply be a form of geometric mean temperature between the minimum time-dependent Hawking Hubble temperature and the maximum Planck temperature of the expanding universe over the course of cosmic time. This mathematical discovery suggests a re-consideration of Rh=ctcosmological models, including black hole cosmological models, even if it possibly could also be consistent with the Λ-CDM model. Most importantly, this paper contributes to the growing literature in the past year asserting a tightly constrained mathematical relationship between the CMB temperature, the Hubble constant, and other global parameters of the Hubble sphere. Our approach suggests a solid theoretical framework for predicting and understanding the CMB temperature rather than solely observing it.1.展开更多
A complementarity hypothesis concerning outsider and insider perspectives of a gargantuan black hole is proposed. The two thought experiments presented herein are followed by a brief discussion of a new interpretation...A complementarity hypothesis concerning outsider and insider perspectives of a gargantuan black hole is proposed. The two thought experiments presented herein are followed by a brief discussion of a new interpretation of black hole interior “space-and-time-reversal”. Specifically, it is proposed that the “singularity” space of the black hole interior is time-like and the expansion time of the black hole interior is space-like. The resemblance of this new insider interpretation to our own expanding and redshifting big bang universe is compelling.展开更多
We explore the variable generalized Chaplygin gas(VGCG)model in the theory of matter creation cosmology within the framework of a spatially homogeneous and isotropic flat Friedmann—Lemai tre—Robertson—Walker space-...We explore the variable generalized Chaplygin gas(VGCG)model in the theory of matter creation cosmology within the framework of a spatially homogeneous and isotropic flat Friedmann—Lemai tre—Robertson—Walker space-time.Matter creation cosmology is based on reinterpretation of the energy–momentum tensor in Einstein's field equations.This creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents.The variable Chaplygin gas(VCG)is also studied as a particular solution.We use the Markov chain Monte Carlo method to constrain the free parameters of three models,namely,Lambda-Cold-Dark matter(ΛCDM),VGCG and VCG models with and without matter creation from the latest observational data from baryon acoustic oscillations,cosmic chronometer,type Ia supernovae(Pantheon)including gamma-ray bursts,quasars and the local measurement of H_(0) from R21 data.Two different combinations of dataset provide a fairly tight constraint on the parameters of theΛCDM,VGCG and VCG models.The present values of various cosmological parameters are obtained,which are very close to theΛCDM model.Furthermore,we perform stability analysis,Bayesian evidence analysis and information criteria analysis for these models through studying the sound speed,Bayes factor,and Akaike information criteria(AIC)and Bayesian information criteria(BIC)selection criteria.The values of sound speed for VGCG and VCG models shows that both the models are stable.According to AIC,it is observed that VGCG and VCG models with matter creation are supported considerably less by current observations,while BIC shows that these models are not favoured by observational data.展开更多
Based our previous work [Mod. Phys. Lett. A 22 （2007） 783, Gen. Relat. Gray. 39 （2007） 653], some properties of modified Chaplygin gas （MCG） as a dark energy model continue to be studied mainly in two aspects： ...Based our previous work [Mod. Phys. Lett. A 22 （2007） 783, Gen. Relat. Gray. 39 （2007） 653], some properties of modified Chaplygin gas （MCG） as a dark energy model continue to be studied mainly in two aspects： one is the change rates of the energy density and energy transfer, and the other is the evolution of the growth index. It is pointed that the density of dark energy undergoes the change from decrease to increase no matter whether the interaction between dark energy and dark matter exists or not, but the corresponding transformation points are different from each other.Eurthermore, it is stressed that the MCG model even supports the existence of interaction between dark energy and dark matter, and the energy of transfer flows from dark energy to dark matter. The evolution of the interaction term with an ansatz 3Hc^2ρ is discussed with the MCG model. Moreover, the evolution of the growth index f in the MCG model without interaction is illustrated, from which we find that the evolutionary trajectory of f overlaps with that of the ACDM model when a 〉 0.7 and its theoretical value f ≈ 0.566 given by us at z = 0.15 is consistent with the observations.展开更多
General Relativity implies an expanding Universe from a singularity, the so-called Big Bang. The rate of expansion is the Hubble constant. There are two major ways of measuring the expansion of the Universe: through t...General Relativity implies an expanding Universe from a singularity, the so-called Big Bang. The rate of expansion is the Hubble constant. There are two major ways of measuring the expansion of the Universe: through the cosmic distance ladder and through looking at the signals originated from the beginning of the Universe. These two methods give quite different results for the Hubble constant. Hence, the Universe doesn’t expand. The solution to this problem is the theory of gravitation in flat space-time where space isn’t expanding. All the results of gravitation for weak fields of this theory agree with those of General Relativity to measurable accuracy whereas at the beginning of the Universe the results of both theories are quite different, i.e. no singularity by gravitation in flat space-time and non-expanding universe, and a Big Bang (singularity) by General Relativity.展开更多
The Brans-Dicke(BD)theory is the simplest Scalar-Tensor theory of gravity,which can be considered as a candidate of modified Einstein’s theory of general relativity.In this work,we forecast the constraints on BD theo...The Brans-Dicke(BD)theory is the simplest Scalar-Tensor theory of gravity,which can be considered as a candidate of modified Einstein’s theory of general relativity.In this work,we forecast the constraints on BD theory in the CSST galaxy clustering spectroscopic survey with a magnitude limit~23 AB mag for point-source 5σdetection.We generate mock data based on the zCOSMOS catalog and consider the observational and instrumental effects of the CSST spectroscopic survey.We predict galaxy power spectra in the BD theory from z=0 to 1.5,and the galaxy bias and other systematical parameters are also included.The Markov Chain Monte Carlo technique is employed to find the best-fits and probability distributions of the cosmological and systematical parameters.A BD parameterζis introduced,which satisfiesζ=In(1+(1/ω)).We find that the CSST spectroscopic galaxy clustering survey can give|ξ|<10^(-2),or equivalently|ω|>O(10^(2))and|■/G|<10^(-13),under the assumptionζ=0.These constraints are almost at the same order of magnitude compared to the joint constraints using the current cosmic microwave background,baryon acoustic oscillations and TypeⅠa supernova data,indicating that the CSST galaxy clustering spectroscopic survey would be powerful for constraining the BD theory and other modified gravity theories.展开更多
We test and explore a Modified Universe Dynamics (MOUND) formula recently proposed by the author. We show that, similarly to Milgrom’s Modified Newtonian Dynamics (MOND), it is successful in accounting for the mass d...We test and explore a Modified Universe Dynamics (MOUND) formula recently proposed by the author. We show that, similarly to Milgrom’s Modified Newtonian Dynamics (MOND), it is successful in accounting for the mass discrepancy in spiral galaxies, and it predicts the Baryonic Tully-Fisher Relation (BTFR) and the Radial Acceleration Relation (RAR). Contrary to Milgrom’s MOND, MOUND also explains the dynamics of galaxy clusters and does not rely on an empirical interpolating function or an ad hoc acceleration parameter.展开更多
We study the interaction between dark energy （DE） and dark matter in the scope of anisotropic Bianchi type-I space-time. First we derive the general form of the DE equation of state （EoS） parameter in both non-int...We study the interaction between dark energy （DE） and dark matter in the scope of anisotropic Bianchi type-I space-time. First we derive the general form of the DE equation of state （EoS） parameter in both non-interacting and interacting cases and then we examine its future by applying a hyperbolic scale factor. It is shown that in the non-interacting case, depending on the value of the anisotropy parameter K, the DE EoS parameter varies from phantom to quintessence whereas in the interacting case the EoS parameter varies in the quintessence region. However, in both cases, the DE EoS parameter ωde ultimately （i.e. at z ： -1） tends to the cosmological constant （ωde = -1）. Moreover, we fix the cosmological bound on the anisotropy parameter K by using recent observational data about the Hubble parameter.展开更多
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.
文摘This paper integrates a quantum conception of the Planck epoch early universe with FSC model formulae and the holographic principle, to offer a reasonable explanation and solution of the cosmological constant problem. Such a solution does not appear to be achievable in cosmological models which do not integrate black hole formulae with quantum formulae such as the Stephan-Boltzmann law. As demonstrated herein, assuming a constant value of Lambda over the great span of cosmic time appears to have been a mistake. It appears that Einstein’s assumption of a constant, in terms of vacuum energy density, was not only a mistake for a statically-balanced universe, but also a mistake for a dynamically-expanding universe.
文摘This brief note brings the reader up-to-date with the recent successes of the new Haug-Tatum cosmology model. In particular, the significance of recent proof that the Stefan-Boltzmann law applies to such a model is emphasized and a rationale for this is given. Remarkably, the proposed solutions of this model have incorporated all 580 supernova redshifts in the Union2 database. Therefore, one can usefully apply this thermodynamic law in the form of a continually expanding black-body universe model. To our knowledge, no other cosmological model has achieved such high-precision observational correlation.
文摘We develop a cosmological model in a physical background scenario of four time and four space dimensions ((4+4)-dimensions or (4+4)-universe). We show that in this framework the (1+3)-universe is deeply connected with the (3+1)-universe. We argue that this means that in the (4+4)-universe there exists a duality relation between the (1+3)-universe and the (3+1)-universe.
基金support (Project No. C.S.T./D-1536) given in part by the State Council of Science and Technology,Uttar Pradesh (U. P.),India is gratefully acknowledged
文摘Motivated by the increasing evidence for the need of a geometry that re- sembles Bianchi morphology to explain the observed anisotropy in the WMAP data, we have discussed some features of Bianchi type VI0 universes in the presence of a fluid that has an anisotropic equation of state （EoS） parameter in general relativity. We present two accelerating dark energy （DE） models with an anisotropic fluid in Bianchi type VI0 space-time. To ensure a deterministic solution, we choose the scale factor a（t） = √tnet, which yields a time-dependent deceleration parameter, representing a class of models which generate a transition of the universe from the early decelerating phase to the recent accelerating phase. Under suitable conditions, the anisotropic mod- els approach an isotropic scenario. The EoS for DE co is found to be time-dependent and its existing range for derived models is in good agreement with data from recent observations of type Ia supernovae （SNe Ia） （Knop et al. 2003）, SNe Ia data com- bined with cosmic microwave background （CMB） anisotropy and galaxy clustering statistics （Tegmark et al. 2004a）, as well as the latest combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift SNe Ia and galaxy clustering. For different values of n, we can generate a class of physically viable DE models. The cosmological constant A is found to be a positive decreasing function of time and it approaches a small positive value at late time （i.e. the present epoch）, which is corroborated by results from recent SN Ia observations. We also ob- serve that our solutions are stable. The physical and geometric aspects of both models are also discussed in detail.
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.
文摘We investigate a two-fluid anisotropic plane symmetric cosmological model with variable gravitational constant G（t） and cosmological term A（t）. In the two-fluid model, one fluid is chosen to be that of the radiation field modeling the cosmic microwave background and the other one a perfect fluid modeling the material content of the universe. Exact solutions of the field equations are obtained by using a special form for the average scale factor which corresponds to a specific time-varying deceleration parameter. The model obtained presents a cosmological scenario which describes an early acceleration and late-time deceleration. The gravitation constant increases with the cosmic time whereas the cosmological term decreases and asymptotically tends to zero. The physical and kinematical behaviors of the associated fluid parameters are discussed.
文摘Spatially homogeneous and anisotropic Bianchi type-I cosmological model containing perfect fluid with quadratic equation of state has been diagnosed in general theory of relativity. To obtain a deterministic solution, we have used a relation between metric potentials. The exact solution of Einstein’s field equations thus obtained represents an expanding and decelerating universe. The physical and kinematical parameters of the model have also been analyzed with certain constrained between the parameters of the quadratic equation of state.
文摘We study the evolution of the dark energy parameter within a Bianchi type-I cosmological model filled with barotropic fluid and dark energy. The solutions have been obtained for power law and exponential forms of the expansion parameter （they correspond to a constant deceleration parameter in general relativity）. After a long time, the models tend to be isotropic under certain conditions.
文摘This article explores the dead universe theory as a novel interpretation for the origin and evolution of the universe, suggesting that our cosmos may have originated from the remnants of a preceding universe. This perspective challenges the conventional Big Bang theory, particularly concerning dark matter, the expansion of the universe, and the interpretation of phenomena such as gravitational waves.
文摘Aims: The expansion of the Universe and gravitation are considered different fundamental properties of the cosmos. We explore whether they are connected and propose an equation that links and unifies them. This equation describes the expansion of space as related to the mass of matter in that space. An expanding frame of reference, defined as expanding at the same rate, is the natural frame for an observer since the observer is part of the Universe and expands with it. In this frame, the expansion of the Universe by itself accounts for phenomena previously ascribed to gravitation. Gravity is fictitious and unnecessary. Here, we show that universal expansion naturally manifests as “gravity”. Methods: A theory is presented that postulates a natural expansion of the observer’s frame of reference due to matter and a generalized universal principle of equivalence of acceleration and gravitation that extends to any frame. It is consistent with both the general theory of relativity and our knowledge about the expansion of the Universe. Results: We tested the theory positively by applying its equation to global and local scales of the Universe with available data. It is applied to a Universe of homogeneous mass and discrete two and three-body systems and other phenomena hitherto thought to be unrelated. The results show that the proposed equation is valid at any scale. The fundamental nature of the Universe, from which gravity and other properties are derived, is its expansion.
文摘Using a rigorous mathematical approach, we demonstrate how the Cosmic Microwave Background (CMB) temperature could simply be a form of geometric mean temperature between the minimum time-dependent Hawking Hubble temperature and the maximum Planck temperature of the expanding universe over the course of cosmic time. This mathematical discovery suggests a re-consideration of Rh=ctcosmological models, including black hole cosmological models, even if it possibly could also be consistent with the Λ-CDM model. Most importantly, this paper contributes to the growing literature in the past year asserting a tightly constrained mathematical relationship between the CMB temperature, the Hubble constant, and other global parameters of the Hubble sphere. Our approach suggests a solid theoretical framework for predicting and understanding the CMB temperature rather than solely observing it.1.
文摘A complementarity hypothesis concerning outsider and insider perspectives of a gargantuan black hole is proposed. The two thought experiments presented herein are followed by a brief discussion of a new interpretation of black hole interior “space-and-time-reversal”. Specifically, it is proposed that the “singularity” space of the black hole interior is time-like and the expansion time of the black hole interior is space-like. The resemblance of this new insider interpretation to our own expanding and redshifting big bang universe is compelling.
文摘We explore the variable generalized Chaplygin gas(VGCG)model in the theory of matter creation cosmology within the framework of a spatially homogeneous and isotropic flat Friedmann—Lemai tre—Robertson—Walker space-time.Matter creation cosmology is based on reinterpretation of the energy–momentum tensor in Einstein's field equations.This creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents.The variable Chaplygin gas(VCG)is also studied as a particular solution.We use the Markov chain Monte Carlo method to constrain the free parameters of three models,namely,Lambda-Cold-Dark matter(ΛCDM),VGCG and VCG models with and without matter creation from the latest observational data from baryon acoustic oscillations,cosmic chronometer,type Ia supernovae(Pantheon)including gamma-ray bursts,quasars and the local measurement of H_(0) from R21 data.Two different combinations of dataset provide a fairly tight constraint on the parameters of theΛCDM,VGCG and VCG models.The present values of various cosmological parameters are obtained,which are very close to theΛCDM model.Furthermore,we perform stability analysis,Bayesian evidence analysis and information criteria analysis for these models through studying the sound speed,Bayes factor,and Akaike information criteria(AIC)and Bayesian information criteria(BIC)selection criteria.The values of sound speed for VGCG and VCG models shows that both the models are stable.According to AIC,it is observed that VGCG and VCG models with matter creation are supported considerably less by current observations,while BIC shows that these models are not favoured by observational data.
基金Supported by National Natural Science Foundation of China under Grant No 10475036, and the Scientific Research Foundation of the Higher Education Institute of Liaoning Province under Grant No 05L215.
文摘Based our previous work [Mod. Phys. Lett. A 22 （2007） 783, Gen. Relat. Gray. 39 （2007） 653], some properties of modified Chaplygin gas （MCG） as a dark energy model continue to be studied mainly in two aspects： one is the change rates of the energy density and energy transfer, and the other is the evolution of the growth index. It is pointed that the density of dark energy undergoes the change from decrease to increase no matter whether the interaction between dark energy and dark matter exists or not, but the corresponding transformation points are different from each other.Eurthermore, it is stressed that the MCG model even supports the existence of interaction between dark energy and dark matter, and the energy of transfer flows from dark energy to dark matter. The evolution of the interaction term with an ansatz 3Hc^2ρ is discussed with the MCG model. Moreover, the evolution of the growth index f in the MCG model without interaction is illustrated, from which we find that the evolutionary trajectory of f overlaps with that of the ACDM model when a 〉 0.7 and its theoretical value f ≈ 0.566 given by us at z = 0.15 is consistent with the observations.
文摘General Relativity implies an expanding Universe from a singularity, the so-called Big Bang. The rate of expansion is the Hubble constant. There are two major ways of measuring the expansion of the Universe: through the cosmic distance ladder and through looking at the signals originated from the beginning of the Universe. These two methods give quite different results for the Hubble constant. Hence, the Universe doesn’t expand. The solution to this problem is the theory of gravitation in flat space-time where space isn’t expanding. All the results of gravitation for weak fields of this theory agree with those of General Relativity to measurable accuracy whereas at the beginning of the Universe the results of both theories are quite different, i.e. no singularity by gravitation in flat space-time and non-expanding universe, and a Big Bang (singularity) by General Relativity.
基金the support of MOST2018YFE0120800,2020SKA0110402,NSFC-11822305,NSFC11773031,NSFC-11633004CAS Interdisciplinary Innovation Team+6 种基金the Chinese Academy of Sciences(CAS)instrument grant ZDKYYQ20200008the CAS Strategic Priority Research Program XDA15020200National Natural Science Foundation of China(NSFC,Grant Nos.11773034 and 11633004)the Chinese Academy of Sciences(CAS)Strategic Priority Research Program XDA15020200the CAS Interdisciplinary Innovation Team(JCTD-2019-05)the support of NSFC(Grant Nos.11473044 and 11973047)the Chinese Academy of Science grants QYZDJ-SSW-SLH017 and XDB 23040100。
文摘The Brans-Dicke(BD)theory is the simplest Scalar-Tensor theory of gravity,which can be considered as a candidate of modified Einstein’s theory of general relativity.In this work,we forecast the constraints on BD theory in the CSST galaxy clustering spectroscopic survey with a magnitude limit~23 AB mag for point-source 5σdetection.We generate mock data based on the zCOSMOS catalog and consider the observational and instrumental effects of the CSST spectroscopic survey.We predict galaxy power spectra in the BD theory from z=0 to 1.5,and the galaxy bias and other systematical parameters are also included.The Markov Chain Monte Carlo technique is employed to find the best-fits and probability distributions of the cosmological and systematical parameters.A BD parameterζis introduced,which satisfiesζ=In(1+(1/ω)).We find that the CSST spectroscopic galaxy clustering survey can give|ξ|<10^(-2),or equivalently|ω|>O(10^(2))and|■/G|<10^(-13),under the assumptionζ=0.These constraints are almost at the same order of magnitude compared to the joint constraints using the current cosmic microwave background,baryon acoustic oscillations and TypeⅠa supernova data,indicating that the CSST galaxy clustering spectroscopic survey would be powerful for constraining the BD theory and other modified gravity theories.
文摘We test and explore a Modified Universe Dynamics (MOUND) formula recently proposed by the author. We show that, similarly to Milgrom’s Modified Newtonian Dynamics (MOND), it is successful in accounting for the mass discrepancy in spiral galaxies, and it predicts the Baryonic Tully-Fisher Relation (BTFR) and the Radial Acceleration Relation (RAR). Contrary to Milgrom’s MOND, MOUND also explains the dynamics of galaxy clusters and does not rely on an empirical interpolating function or an ad hoc acceleration parameter.
基金a research fund from the Mahshahr Branch of Islamic Azad University under the project entitled "Interacting Viscous Dark Energy And Cold Dark Matter In An Anisotropic Universe"
文摘We study the interaction between dark energy （DE） and dark matter in the scope of anisotropic Bianchi type-I space-time. First we derive the general form of the DE equation of state （EoS） parameter in both non-interacting and interacting cases and then we examine its future by applying a hyperbolic scale factor. It is shown that in the non-interacting case, depending on the value of the anisotropy parameter K, the DE EoS parameter varies from phantom to quintessence whereas in the interacting case the EoS parameter varies in the quintessence region. However, in both cases, the DE EoS parameter ωde ultimately （i.e. at z ： -1） tends to the cosmological constant （ωde = -1）. Moreover, we fix the cosmological bound on the anisotropy parameter K by using recent observational data about the Hubble parameter.
