In this paper,we study the rotation curves of the Milky Way galaxy and Andromeda galaxy(M31)by considering their bulge,disk,and halo components.We model the bulge region by the widely accepted de Vaucouleur’s law and...In this paper,we study the rotation curves of the Milky Way galaxy and Andromeda galaxy(M31)by considering their bulge,disk,and halo components.We model the bulge region by the widely accepted de Vaucouleur’s law and the disk region by the well established exponential profile.In order to understand the distribution of dark matter in the halo region,we consider three different dark matter profiles in the framework of the standardΛCDM model namely,Navarro-Frenk-White(NFW),Hernquist and Einasto profiles.We use recent data sets of rotation curves of the Milky Way and Andromeda galaxy.The data consist of rotation velocities of the stars and gas in the galaxy as a function of the radial distance from the center.Using Bayesian statistics,we perform an overall fit including all the components,i.e.,bulge,disk and halo with the data.Our results indicate that the NFW and Hernquist profiles are in concordance with the observational data points.However,the Einasto profile poorly explains the behavior of dark matter in both the galaxies.展开更多
The universe content is considered as a non-perfect fluid with bulk viscosity and is described by a more general equation of state(endowed some deviation from the conventionally assumed cosmic perfect fluid model).We ...The universe content is considered as a non-perfect fluid with bulk viscosity and is described by a more general equation of state(endowed some deviation from the conventionally assumed cosmic perfect fluid model).We assume the bulk viscosityis a linear combination of two terms:one is constant,and the other is proportional to the scalar expansion 0=3a/a.The equation of state is described as p=(γ-1)p+po,where po is a parameter.In this framework we demonstrate that this model can be used to explain the dark energy dominated universe,and different proper choices of the parameters may lead to three kinds of fates of the cosmological evolution:no future singularity,big rip,or Type-Ⅲsingularity as presented in[S.Nojiri,S.D.Odintsov,and S.Tsujikawa,Phys.Rev.D 71(2005)063004].展开更多
Observational astronomy has shown significant growth over the last decade and has made important contributions to cosmology. A major paradigm shift in cosmology was brought about by observations of Type Ia supernovae....Observational astronomy has shown significant growth over the last decade and has made important contributions to cosmology. A major paradigm shift in cosmology was brought about by observations of Type Ia supernovae. The notion that the universe is accelerating has led to several theoretical challenges. Unfortunately, although high-quality supernovae data-sets are being produced, their statistical anal- ysis leaves much to be desired. Instead of using the data to directly test the model, several studies seem to concentrate on assuming the model to be correct and limiting themselves to estimating model parameters and internal errors. As shown here, the important purpose of testing a cosmological theory is thereby vitiated.展开更多
A superbubble which advances in a symmetric Navarro-Frenk-White density profile or in an auto-gravitating density profile generates a thick shell with a radius that can reach 10 kpc. The application of the symmetric a...A superbubble which advances in a symmetric Navarro-Frenk-White density profile or in an auto-gravitating density profile generates a thick shell with a radius that can reach 10 kpc. The application of the symmetric and asymmetric image theory to this thick 3D shell produces a ring in the 2D map of intensity and a characteristic “U” shape in the case of 1D cut of the intensity. A comparison of such a ring originating from a superbubble is made with the Einstein’s ring. A Taylor approximation of order 10 for the angular diameter distance is derived in order to deal with high values of the redshift.展开更多
We reduplicate the Book “Dark Energy” by M. Li, X.-D. Li, and Y. Wang, zero-point energy calculation with an unexpected “length” added to the “width” of a graviton wavefunction just prior to the entrance of “gr...We reduplicate the Book “Dark Energy” by M. Li, X.-D. Li, and Y. Wang, zero-point energy calculation with an unexpected “length” added to the “width” of a graviton wavefunction just prior to the entrance of “gravitons” to a small region of space-time prior to a nonsingular start to the universe. We compare this to a solution which worked out using Klauder Enhanced quantization, for the same given problem. The solution of the first Cosmological Constant problem relies upon the geometry of the multiverse generalization of CCC cosmology which is explained in this paper. The second solution used involves Klauder enhanced quantization. We look at energy given by our methods and compare and contrast it with the negative energy of the Rosen model for a mini sub-universe and estimate GW frequencies.展开更多
A new analytical solution for the luminosity distance in flat ΛCDM cosmology is derived in terms of elliptical integrals of first kind with real argument. The consequent derivation of the distance modulus allows eval...A new analytical solution for the luminosity distance in flat ΛCDM cosmology is derived in terms of elliptical integrals of first kind with real argument. The consequent derivation of the distance modulus allows evaluating the Hubble constant, H0=69.77±0.33, ΩM=0.295±0.008, and the cosmological constant, .展开更多
The Doppler formula should be used directly to calculate red shift of Cosmology. The first is gravity, the second is the Doppler’s effect and the third is the Compton scattering. The red shift of cosmology is conside...The Doppler formula should be used directly to calculate red shift of Cosmology. The first is gravity, the second is the Doppler’s effect and the third is the Compton scattering. The red shift of cosmology is considered to be caused by the receding motions of celestial bodies, of which essence is the Doppler’s effect. However, the basic formula used to calculate the relationship between red shift and distance for Ia supernova in cosmology is z+1= R(t0)/R(t1)which is based on the R-W metric and related to the scalar factor R(t). This is different from the Doppler formula which is related to speed factor R(t). Because the R-W metric is only a mathematical structure of space, the metric red shift is not an independent law of physics, this inconsistence is not allowed in physics. It is proved strictly in this paper that the formula of metric red shift is only the result of the first order approximation. If higher order approximations are considered, we can obtain a restrict condition R(t). It indicates that if the formula of metric red shift holds, it can only be suitable to describe the spatial uniform expansion, unsuitable for the practical universal process with acceleration. The further study reveals that the R-W metric violates the invariability principle of light’s speed in vacuum. The time delay caused by展开更多
We present an analytical solution for the luminosity distance in spatially flat cosmology with pressureless matter and the cosmological constant. The complex analytical solution is made of a real part and a negligible...We present an analytical solution for the luminosity distance in spatially flat cosmology with pressureless matter and the cosmological constant. The complex analytical solution is made of a real part and a negligible imaginary part. The real part of the luminosity distance allows finding the two parameters H<sub>0</sub> and Ω<sub>M</sub> . A simple expression for the distance modulus for SNs of type Ia is reported in the framework of the mini-max approximation.展开更多
The quantum properties of O（2,2） string cosmology with a dilaton potential are studied in this paper. The cosmological solutions are obtained on three-dlmensional space-time. Moreover, the quantum probability of tra...The quantum properties of O（2,2） string cosmology with a dilaton potential are studied in this paper. The cosmological solutions are obtained on three-dlmensional space-time. Moreover, the quantum probability of transition between two duality universe is calculated through a Wheeler-De Witt approach.展开更多
The universe content is considered as a non-perfect fluid with bulk viscosity and can be described by a general equation of state （endowed some deviation from the conventionally assumed cosmic perfect fluid model）. ...The universe content is considered as a non-perfect fluid with bulk viscosity and can be described by a general equation of state （endowed some deviation from the conventionally assumed cosmic perfect fluid model）. An explicitly bulk viscosity dark energy model is proposed to confront consistently with the current observational data sets by statistical analysis and is shown consistent with （not deviated away much from） the concordant A Cold Dark Matter （CDM） model by comparing the decelerating parameter. Also we compare our relatively simple viscosity dark energy model with a more complicated one by contrast with the concordant ACDM model and find our model improves for the viscosity dark energy model building. Finally we discuss the perspectives of dark energy probes for the coming years with observations.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
This paper describes the propulsion principle using the concept of space drive and the pressure of the field induced by local rapid expansion of space based on the latest cosmology. Assuming that space vacuum is an in...This paper describes the propulsion principle using the concept of space drive and the pressure of the field induced by local rapid expansion of space based on the latest cosmology. Assuming that space vacuum is an infinite continuum, the propulsion principle utilizes the pressure field derived from the geometrical structure of space, by applying both continuum mechanics and general relativity to space. The propulsive force is a pressure thrust that arises from the interaction of space-time around the spaceship external environment and the spaceship itself; the spaceship is propelled by the pressure used against the space-time structure. As is well known in cosmology, the expansion rule of the universe is governed by the Friedman＇s equations and the Robertson-Walker metric. In this time, the propulsion principle of space drive is introduced from another angle （cosmology）, that is, the pressure of the field induced by local expansion of space is completely considered in the propulsion principle.展开更多
The descriptive capabilities of the banded speed cosmological model are shown. In particular, an in-depth analysis related to the actual physical meaning of Planck＇s unit is given in the framework of the banded distr...The descriptive capabilities of the banded speed cosmological model are shown. In particular, an in-depth analysis related to the actual physical meaning of Planck＇s unit is given in the framework of the banded distribution of physical quantities. From this analysis the richness and flexibility of the model＇s description capabilities is derived, with particular attention devoted to the ability of using the same relationships for describing both microcosm and macrocosm and also young and old universe. Finally the cited descriptive capabilities are used for deriving a very simple and intuitive explanation of the ＂darkness＂ of dark matter.展开更多
We investigate direction dependence and non-Gaussian features in high-z cosmological data using ?_(χ~2) and ?_χ statistics and the Kolmogorov-Smirnov test. These techniques are applied on a set of calibrated long ga...We investigate direction dependence and non-Gaussian features in high-z cosmological data using ?_(χ~2) and ?_χ statistics and the Kolmogorov-Smirnov test. These techniques are applied on a set of calibrated long gamma-ray bursts(GRBs) and its combination with recent Type Ia supernovae data(Union2). Our statistical analysis shows a weak but consistent direction dependence in both the data sets.The analysis also indicates a non-Gaussian nature of errors in both data sets.展开更多
In recent works, a construction was proposed resulting in emergent universes inside black holes. This result can be obtained from a 4D black hole embedded in a 5D spacetime with the fifth dimension compactified on a c...In recent works, a construction was proposed resulting in emergent universes inside black holes. This result can be obtained from a 4D black hole embedded in a 5D spacetime with the fifth dimension compactified on a circle [0, 2] (0 and 2 are identified) such that the two branes are at 0 and 1. In the present work, we study this setup by deriving particles’ equations of motion in the new universes, based on redefining energy and angular momentum. This leads to disappearance of the singularity in centers of black holes in classical General Relativity.展开更多
In this work, we consider the so-called Λ(α)CDM cosmology with Λ∝α^(-6) while the fine-structure"constant" α is varying. In this scenario, the accelerated expansion of the universe is driven by the cos...In this work, we consider the so-called Λ(α)CDM cosmology with Λ∝α^(-6) while the fine-structure"constant" α is varying. In this scenario, the accelerated expansion of the universe is driven by the cosmological"constant" Λ(equivalently the vacuum energy), and the varying α is driven by a subdominant scalar field ? coupling with the electromagnetic field. The observational constraints on the varying α and Λ∝α^(-6) models with various couplings BF(?) between the subdominant scalar field ? and the electromagnetic field are considered.展开更多
Varying speed of light （VSL） has been used in cosmological models in which the physical constants vary over time. On the other hand, the Dvali, Gabadadze and Porrati （DGP） brahe world model, especially its normal ...Varying speed of light （VSL） has been used in cosmological models in which the physical constants vary over time. On the other hand, the Dvali, Gabadadze and Porrati （DGP） brahe world model, especially its normal branch, has been extensively discussed to justify the current cosmic acceleration. In this article we show that the normal branch of DGP in VSL cosmology leads to a self-accelerating behavior and therefore can interpret cosmic acceleration. Applying statefinder diagnostics demonstrates that our result slightly deviates from the ACDM model.展开更多
We study thermodynamics of the parabolic Lemaitre-Tolman-Bondi(LTB) cosmology supported by a perfect Suid source.This model is the natural generalization of the Sat Friedmann-Robertson-Walker(FRW) universe,and describ...We study thermodynamics of the parabolic Lemaitre-Tolman-Bondi(LTB) cosmology supported by a perfect Suid source.This model is the natural generalization of the Sat Friedmann-Robertson-Walker(FRW) universe,and describes an inhomogeneous universe with spherical symmetry.After reviewing some basic equations in the parabolic LTB cosmology,we obtain a relation for the deceleration parameter in this model.We also obtain a condition for which the universe undergoes an accelerating phase at the present time.We use the first law of thermodynamics on the apparent horizon together with the Einstein field equations to get a relation for the apparent horizon entropy in LTB cosmology.We find out that in LTB model of cosmology,the apparent horizon's entropy could be feeded by a term,which incorporates the effects of the inhomogeneity.We consider this result and get a relation for the total entropy evolution,which is used to examine the generalized second law of thermodynamics for an accelerating universe.We also verify the validity of the second law and the generalized second law of thermodynamics for a universe filled with some kinds of matters bounded by the event horizon in the framework of the parabolic LTB model.展开更多
In this paper we have searched for the existence of Lyra’s cosmology in a hybrid universe with minimal interaction between dark energy and normal matter using Bianchi-V space-time. To derive the exact solution, the a...In this paper we have searched for the existence of Lyra’s cosmology in a hybrid universe with minimal interaction between dark energy and normal matter using Bianchi-V space-time. To derive the exact solution, the average scale factor is taken as a =(t~nekt)1/m which describes the hybrid nature of the scale factor and generates a model of the transitioning universe from the early deceleration phase to the present acceleration phase. The quintessence model makes the matter content of the derived universe remarkably able to satisfy the null, dominant and strong energy condition. It has been found that the time varying displacement β(t) co-relates with the nature of cosmological constant Λ(t). We also discuss some physical and geometrical features of the universe.展开更多
We discuss a particular four-dimensional cosmology based on non-minimal scalar tensor theories characterized by a supersymmetric loop corrected potential and a Hubble parameter defined as a function of the scalar fiel...We discuss a particular four-dimensional cosmology based on non-minimal scalar tensor theories characterized by a supersymmetric loop corrected potential and a Hubble parameter defined as a function of the scalar field.Power-law solutions are obtained in the FRW background giving rise to acceleratedly expanding universe characterized by a scale factor and a scalar field depending both on the non-minimal coupling parameterξ.Based on SNeIa data and on Hubble data X-ray gas mass fraction measurements,we find 0.116<ξ<0.225 which results on a universe dominated by vacuum energy.展开更多
基金supported by the Startup Research Fund of the Henan Academy of Sciences under grant No.241841219。
文摘In this paper,we study the rotation curves of the Milky Way galaxy and Andromeda galaxy(M31)by considering their bulge,disk,and halo components.We model the bulge region by the widely accepted de Vaucouleur’s law and the disk region by the well established exponential profile.In order to understand the distribution of dark matter in the halo region,we consider three different dark matter profiles in the framework of the standardΛCDM model namely,Navarro-Frenk-White(NFW),Hernquist and Einasto profiles.We use recent data sets of rotation curves of the Milky Way and Andromeda galaxy.The data consist of rotation velocities of the stars and gas in the galaxy as a function of the radial distance from the center.Using Bayesian statistics,we perform an overall fit including all the components,i.e.,bulge,disk and halo with the data.Our results indicate that the NFW and Hernquist profiles are in concordance with the observational data points.However,the Einasto profile poorly explains the behavior of dark matter in both the galaxies.
基金The project partly supported by National Natural Science Foundation of China under Grant No.10675062the Doctoral Foundation of China We thank Profs.I.Brevik,S.D.0dintsov,and Lewis H.Ryder for lots of interesting discussions.
文摘The universe content is considered as a non-perfect fluid with bulk viscosity and is described by a more general equation of state(endowed some deviation from the conventionally assumed cosmic perfect fluid model).We assume the bulk viscosityis a linear combination of two terms:one is constant,and the other is proportional to the scalar expansion 0=3a/a.The equation of state is described as p=(γ-1)p+po,where po is a parameter.In this framework we demonstrate that this model can be used to explain the dark energy dominated universe,and different proper choices of the parameters may lead to three kinds of fates of the cosmological evolution:no future singularity,big rip,or Type-Ⅲsingularity as presented in[S.Nojiri,S.D.Odintsov,and S.Tsujikawa,Phys.Rev.D 71(2005)063004].
文摘Observational astronomy has shown significant growth over the last decade and has made important contributions to cosmology. A major paradigm shift in cosmology was brought about by observations of Type Ia supernovae. The notion that the universe is accelerating has led to several theoretical challenges. Unfortunately, although high-quality supernovae data-sets are being produced, their statistical anal- ysis leaves much to be desired. Instead of using the data to directly test the model, several studies seem to concentrate on assuming the model to be correct and limiting themselves to estimating model parameters and internal errors. As shown here, the important purpose of testing a cosmological theory is thereby vitiated.
文摘A superbubble which advances in a symmetric Navarro-Frenk-White density profile or in an auto-gravitating density profile generates a thick shell with a radius that can reach 10 kpc. The application of the symmetric and asymmetric image theory to this thick 3D shell produces a ring in the 2D map of intensity and a characteristic “U” shape in the case of 1D cut of the intensity. A comparison of such a ring originating from a superbubble is made with the Einstein’s ring. A Taylor approximation of order 10 for the angular diameter distance is derived in order to deal with high values of the redshift.
文摘We reduplicate the Book “Dark Energy” by M. Li, X.-D. Li, and Y. Wang, zero-point energy calculation with an unexpected “length” added to the “width” of a graviton wavefunction just prior to the entrance of “gravitons” to a small region of space-time prior to a nonsingular start to the universe. We compare this to a solution which worked out using Klauder Enhanced quantization, for the same given problem. The solution of the first Cosmological Constant problem relies upon the geometry of the multiverse generalization of CCC cosmology which is explained in this paper. The second solution used involves Klauder enhanced quantization. We look at energy given by our methods and compare and contrast it with the negative energy of the Rosen model for a mini sub-universe and estimate GW frequencies.
文摘A new analytical solution for the luminosity distance in flat ΛCDM cosmology is derived in terms of elliptical integrals of first kind with real argument. The consequent derivation of the distance modulus allows evaluating the Hubble constant, H0=69.77±0.33, ΩM=0.295±0.008, and the cosmological constant, .
文摘The Doppler formula should be used directly to calculate red shift of Cosmology. The first is gravity, the second is the Doppler’s effect and the third is the Compton scattering. The red shift of cosmology is considered to be caused by the receding motions of celestial bodies, of which essence is the Doppler’s effect. However, the basic formula used to calculate the relationship between red shift and distance for Ia supernova in cosmology is z+1= R(t0)/R(t1)which is based on the R-W metric and related to the scalar factor R(t). This is different from the Doppler formula which is related to speed factor R(t). Because the R-W metric is only a mathematical structure of space, the metric red shift is not an independent law of physics, this inconsistence is not allowed in physics. It is proved strictly in this paper that the formula of metric red shift is only the result of the first order approximation. If higher order approximations are considered, we can obtain a restrict condition R(t). It indicates that if the formula of metric red shift holds, it can only be suitable to describe the spatial uniform expansion, unsuitable for the practical universal process with acceleration. The further study reveals that the R-W metric violates the invariability principle of light’s speed in vacuum. The time delay caused by
文摘We present an analytical solution for the luminosity distance in spatially flat cosmology with pressureless matter and the cosmological constant. The complex analytical solution is made of a real part and a negligible imaginary part. The real part of the luminosity distance allows finding the two parameters H<sub>0</sub> and Ω<sub>M</sub> . A simple expression for the distance modulus for SNs of type Ia is reported in the framework of the mini-max approximation.
基金The project supported by the Natural Science Foundation of Sichuan Normal University
文摘The quantum properties of O（2,2） string cosmology with a dilaton potential are studied in this paper. The cosmological solutions are obtained on three-dlmensional space-time. Moreover, the quantum probability of transition between two duality universe is calculated through a Wheeler-De Witt approach.
基金Supported by the National Natural Science Foundation of China under Grant No.10675062the Project of Knowledge Innovation Program (PKIP) of Chinese Academy of Sciences under Grant No.KJCX2.YW.W10
文摘The universe content is considered as a non-perfect fluid with bulk viscosity and can be described by a general equation of state （endowed some deviation from the conventionally assumed cosmic perfect fluid model）. An explicitly bulk viscosity dark energy model is proposed to confront consistently with the current observational data sets by statistical analysis and is shown consistent with （not deviated away much from） the concordant A Cold Dark Matter （CDM） model by comparing the decelerating parameter. Also we compare our relatively simple viscosity dark energy model with a more complicated one by contrast with the concordant ACDM model and find our model improves for the viscosity dark energy model building. Finally we discuss the perspectives of dark energy probes for the coming years with observations.
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This paper describes the propulsion principle using the concept of space drive and the pressure of the field induced by local rapid expansion of space based on the latest cosmology. Assuming that space vacuum is an infinite continuum, the propulsion principle utilizes the pressure field derived from the geometrical structure of space, by applying both continuum mechanics and general relativity to space. The propulsive force is a pressure thrust that arises from the interaction of space-time around the spaceship external environment and the spaceship itself; the spaceship is propelled by the pressure used against the space-time structure. As is well known in cosmology, the expansion rule of the universe is governed by the Friedman＇s equations and the Robertson-Walker metric. In this time, the propulsion principle of space drive is introduced from another angle （cosmology）, that is, the pressure of the field induced by local expansion of space is completely considered in the propulsion principle.
文摘The descriptive capabilities of the banded speed cosmological model are shown. In particular, an in-depth analysis related to the actual physical meaning of Planck＇s unit is given in the framework of the banded distribution of physical quantities. From this analysis the richness and flexibility of the model＇s description capabilities is derived, with particular attention devoted to the ability of using the same relationships for describing both microcosm and macrocosm and also young and old universe. Finally the cited descriptive capabilities are used for deriving a very simple and intuitive explanation of the ＂darkness＂ of dark matter.
文摘We investigate direction dependence and non-Gaussian features in high-z cosmological data using ?_(χ~2) and ?_χ statistics and the Kolmogorov-Smirnov test. These techniques are applied on a set of calibrated long gamma-ray bursts(GRBs) and its combination with recent Type Ia supernovae data(Union2). Our statistical analysis shows a weak but consistent direction dependence in both the data sets.The analysis also indicates a non-Gaussian nature of errors in both data sets.
文摘In recent works, a construction was proposed resulting in emergent universes inside black holes. This result can be obtained from a 4D black hole embedded in a 5D spacetime with the fifth dimension compactified on a circle [0, 2] (0 and 2 are identified) such that the two branes are at 0 and 1. In the present work, we study this setup by deriving particles’ equations of motion in the new universes, based on redefining energy and angular momentum. This leads to disappearance of the singularity in centers of black holes in classical General Relativity.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11575022 and 11175016
文摘In this work, we consider the so-called Λ(α)CDM cosmology with Λ∝α^(-6) while the fine-structure"constant" α is varying. In this scenario, the accelerated expansion of the universe is driven by the cosmological"constant" Λ(equivalently the vacuum energy), and the varying α is driven by a subdominant scalar field ? coupling with the electromagnetic field. The observational constraints on the varying α and Λ∝α^(-6) models with various couplings BF(?) between the subdominant scalar field ? and the electromagnetic field are considered.
文摘Varying speed of light （VSL） has been used in cosmological models in which the physical constants vary over time. On the other hand, the Dvali, Gabadadze and Porrati （DGP） brahe world model, especially its normal branch, has been extensively discussed to justify the current cosmic acceleration. In this article we show that the normal branch of DGP in VSL cosmology leads to a self-accelerating behavior and therefore can interpret cosmic acceleration. Applying statefinder diagnostics demonstrates that our result slightly deviates from the ACDM model.
基金Supported financially by Research Institute for Astronomy&Astrophysics of Maragha(RIAAM),Iran
文摘We study thermodynamics of the parabolic Lemaitre-Tolman-Bondi(LTB) cosmology supported by a perfect Suid source.This model is the natural generalization of the Sat Friedmann-Robertson-Walker(FRW) universe,and describes an inhomogeneous universe with spherical symmetry.After reviewing some basic equations in the parabolic LTB cosmology,we obtain a relation for the deceleration parameter in this model.We also obtain a condition for which the universe undergoes an accelerating phase at the present time.We use the first law of thermodynamics on the apparent horizon together with the Einstein field equations to get a relation for the apparent horizon entropy in LTB cosmology.We find out that in LTB model of cosmology,the apparent horizon's entropy could be feeded by a term,which incorporates the effects of the inhomogeneity.We consider this result and get a relation for the total entropy evolution,which is used to examine the generalized second law of thermodynamics for an accelerating universe.We also verify the validity of the second law and the generalized second law of thermodynamics for a universe filled with some kinds of matters bounded by the event horizon in the framework of the parabolic LTB model.
文摘In this paper we have searched for the existence of Lyra’s cosmology in a hybrid universe with minimal interaction between dark energy and normal matter using Bianchi-V space-time. To derive the exact solution, the average scale factor is taken as a =(t~nekt)1/m which describes the hybrid nature of the scale factor and generates a model of the transitioning universe from the early deceleration phase to the present acceleration phase. The quintessence model makes the matter content of the derived universe remarkably able to satisfy the null, dominant and strong energy condition. It has been found that the time varying displacement β(t) co-relates with the nature of cosmological constant Λ(t). We also discuss some physical and geometrical features of the universe.
文摘We discuss a particular four-dimensional cosmology based on non-minimal scalar tensor theories characterized by a supersymmetric loop corrected potential and a Hubble parameter defined as a function of the scalar field.Power-law solutions are obtained in the FRW background giving rise to acceleratedly expanding universe characterized by a scale factor and a scalar field depending both on the non-minimal coupling parameterξ.Based on SNeIa data and on Hubble data X-ray gas mass fraction measurements,we find 0.116<ξ<0.225 which results on a universe dominated by vacuum energy.
