We investigated some Friedmann-Lemaître-Robertson-Walker(FLRW)cosmological models in the context of metric-affine F(R,Q)gravity,as proposed in[arXiv:1205.5266v6].Here,R and Q are the curvature and nonmetricity sc...We investigated some Friedmann-Lemaître-Robertson-Walker(FLRW)cosmological models in the context of metric-affine F(R,Q)gravity,as proposed in[arXiv:1205.5266v6].Here,R and Q are the curvature and nonmetricity scalars using non-special connections,respectively.We obtained the modified field equations using a flat FLRW metric.We then found a connection between the Hubble constant H_(0),density parameter Ω_(m0),and other model parameters in two different situations involving scalars u and w.Next,we used new observational datasets,such as the cosmic chronometer(CC)Hubble and Pantheon SNe Ia datasets,to determine the optimal model parameter values through a Markov chain Monte Carlo(MCMC)analysis.Using these best-fit values of the model parameters,we discussed the results and behavior of the derived models.Further,we discussed the Akaike information criterion(AIC)and Bayesian information criterion(BIC)for the derived models in the context of the Lambda cold dark matter(ΛCDM).We found that the geometrical sector dark equation of state parameter ω_(de)behaves just like a dark energy candidate.We also found that both models are transit phase models.Model-Ⅰ approaches the ΛCDM model in the late-time universe,whereas Model-Ⅱ approaches quintessence scenarios.展开更多
We are interested in the classical solutions to the Cauchy problem of relativistic Burgers equations evolving in Friedmann-Lemat?tre-Robertson-Walker(FLRW)space-times,which are spatially homogeneous,isotropic expandin...We are interested in the classical solutions to the Cauchy problem of relativistic Burgers equations evolving in Friedmann-Lemat?tre-Robertson-Walker(FLRW)space-times,which are spatially homogeneous,isotropic expanding or contracting universes.In such kind of space-times,we first derive the relativistic Burgers equations from the relativistic Euler equations by letting the pressure be zero.Then we can show the global existence of the classical solution to the derived equation in the accelerated expanding space-times with small initial data by the method of characteristics when the spacial dimension n=1 and the energy estimate when n 2,respectively.Furthermore,we can also show the lifespan of the classical solution by similar methods when the expansion rate of the space-times is not so fast.展开更多
The quantum electrodynamics(QED)in a spatially flat(1+3)-dimensional Friedmann-Lema?tre-Robertson-Walker(FLRW)space-time with a Milne-type scale factor is outlined focusing on the amplitudes of the allowed processes i...The quantum electrodynamics(QED)in a spatially flat(1+3)-dimensional Friedmann-Lema?tre-Robertson-Walker(FLRW)space-time with a Milne-type scale factor is outlined focusing on the amplitudes of the allowed processes in the first order perturbations.The definition of the transition rates is reconsidered such that an appropriate angular behavior of the probability for creation of an electron-positron pair from a photon is obtained,which has a similar rate as the creation of a photon and an electron-positron pair from vacuum.It is shown that these processes are allowed only in the first order perturbations,since the photon emission or absorption by an electron or positron are forbidden.展开更多
The kinematics on spatially flat FLRW spacetimes is presented for the first time in local charts with physical coordinates,i.e.,the cosmic time and proper Cartesian space coordinates of Painlevé-type.It is shown ...The kinematics on spatially flat FLRW spacetimes is presented for the first time in local charts with physical coordinates,i.e.,the cosmic time and proper Cartesian space coordinates of Painlevé-type.It is shown that there exists a conserved momentum that determines the form of the covariant four-momentum on geodesics in terms of physical coordinates.Moreover,with the help of this conserved momentum,the peculiar momentum can be defined,thus separating the peculiar and recessional motions without ambiguity.It is shown that the energy and peculiar momentum satisfy the mass-shell condition of special relativity while the recessional momentum does not produce energy.In this framework,the measurements of the kinetic quantities along geodesics performed by different observers are analyzed,pointing out an energy loss of the massive particles similar to that producing the photon redshift.The examples of the kinematics on the de Sitter expanding universe and a new Milne-type spacetime are extensively analyzed.展开更多
基金Supported by the Ministry of Science and Higher Education of the Republic of Kazakhstan(AP14870191)。
文摘We investigated some Friedmann-Lemaître-Robertson-Walker(FLRW)cosmological models in the context of metric-affine F(R,Q)gravity,as proposed in[arXiv:1205.5266v6].Here,R and Q are the curvature and nonmetricity scalars using non-special connections,respectively.We obtained the modified field equations using a flat FLRW metric.We then found a connection between the Hubble constant H_(0),density parameter Ω_(m0),and other model parameters in two different situations involving scalars u and w.Next,we used new observational datasets,such as the cosmic chronometer(CC)Hubble and Pantheon SNe Ia datasets,to determine the optimal model parameter values through a Markov chain Monte Carlo(MCMC)analysis.Using these best-fit values of the model parameters,we discussed the results and behavior of the derived models.Further,we discussed the Akaike information criterion(AIC)and Bayesian information criterion(BIC)for the derived models in the context of the Lambda cold dark matter(ΛCDM).We found that the geometrical sector dark equation of state parameter ω_(de)behaves just like a dark energy candidate.We also found that both models are transit phase models.Model-Ⅰ approaches the ΛCDM model in the late-time universe,whereas Model-Ⅱ approaches quintessence scenarios.
基金supported by National Natural Science Foundation of China (Grant Nos. 91630311 and 11701517)Fundamental Research Funds for the Central Universities (Grant No. 2017XZZX007-02)the Scientific Research Foundation of Zhejiang Sci-Tech University (Grant No. 16062021-Y)
文摘We are interested in the classical solutions to the Cauchy problem of relativistic Burgers equations evolving in Friedmann-Lemat?tre-Robertson-Walker(FLRW)space-times,which are spatially homogeneous,isotropic expanding or contracting universes.In such kind of space-times,we first derive the relativistic Burgers equations from the relativistic Euler equations by letting the pressure be zero.Then we can show the global existence of the classical solution to the derived equation in the accelerated expanding space-times with small initial data by the method of characteristics when the spacial dimension n=1 and the energy estimate when n 2,respectively.Furthermore,we can also show the lifespan of the classical solution by similar methods when the expansion rate of the space-times is not so fast.
文摘The quantum electrodynamics(QED)in a spatially flat(1+3)-dimensional Friedmann-Lema?tre-Robertson-Walker(FLRW)space-time with a Milne-type scale factor is outlined focusing on the amplitudes of the allowed processes in the first order perturbations.The definition of the transition rates is reconsidered such that an appropriate angular behavior of the probability for creation of an electron-positron pair from a photon is obtained,which has a similar rate as the creation of a photon and an electron-positron pair from vacuum.It is shown that these processes are allowed only in the first order perturbations,since the photon emission or absorption by an electron or positron are forbidden.
文摘The kinematics on spatially flat FLRW spacetimes is presented for the first time in local charts with physical coordinates,i.e.,the cosmic time and proper Cartesian space coordinates of Painlevé-type.It is shown that there exists a conserved momentum that determines the form of the covariant four-momentum on geodesics in terms of physical coordinates.Moreover,with the help of this conserved momentum,the peculiar momentum can be defined,thus separating the peculiar and recessional motions without ambiguity.It is shown that the energy and peculiar momentum satisfy the mass-shell condition of special relativity while the recessional momentum does not produce energy.In this framework,the measurements of the kinetic quantities along geodesics performed by different observers are analyzed,pointing out an energy loss of the massive particles similar to that producing the photon redshift.The examples of the kinematics on the de Sitter expanding universe and a new Milne-type spacetime are extensively analyzed.
