Recently the background independent nonperturbative quantization has been extended to various theories of gravity and the corresponding quantum effective cosmology has been derived, which provides us with necessary av...Recently the background independent nonperturbative quantization has been extended to various theories of gravity and the corresponding quantum effective cosmology has been derived, which provides us with necessary avenue to explore the pre-inflationary dynamics. Brans-Dicke(BD) loop quantum cosmology(LQC) is one of such theories whose effective background dynamics is considered in this article. Starting with a quantum bounce, we explore the pre-inflationary dynamics of a universe sourced by a scalar field with the Starobinsky potential in BD-LQC. Our study is based on the idea that though Einstein’s and Jordan’s frames are classically equivalent up to a conformal transformation in BD theory, this is no longer true after quantization. Taking the Jordan frame as the physical one we explore in detail the bouncing scenario which is followed by a phase of a slow roll inflation. The three phases of the evolution of the universe, namely, bouncing, transition from quantum bounce to classical universe, and the slow roll inflation, are noted for an initially kinetic energy dominated bounce. In addition, to be consistent with observations, we also identify the allowed phase space of initial conditions that would produce at least 60 e-folds of expansion during the slow roll inflation.展开更多
We propose a new consistency test for theΛCDM cosmology using baryonic acoustic oscillations(BAO)and redshift space distortion(RSD)measurements from galaxy redshift surveys.Specifically,we determine the peak position...We propose a new consistency test for theΛCDM cosmology using baryonic acoustic oscillations(BAO)and redshift space distortion(RSD)measurements from galaxy redshift surveys.Specifically,we determine the peak position of fσ8(z)in redshift z offered by an RSD measurement,and compare it to the one predicted by the BAO observables assuming a flatΛCDM cosmology.We demonstrate this new test using the simulated data for the DESI galaxy survey,and argue that this test complements those using the background observables alone,and is less subject to systematics in the RSD analysis,compared to traditional methods using values of fσ8(z)directly.展开更多
This model ties gravitation and celestial mechanics and kinematics directly to time dilation. It is a new theory of cosmology and the evolution of galaxies. Space and time are not two separate things, but two aspects ...This model ties gravitation and celestial mechanics and kinematics directly to time dilation. It is a new theory of cosmology and the evolution of galaxies. Space and time are not two separate things, but two aspects of a single thing, “spacetime”. Whatever affects space, affects time, and vice-versa. If time speeds up, space must contract to maintain the speed of light, c, and when space thickens into a mass, it is harder to evolve forward, and time appears to slow. If spatial events are spinning as time passes, then the forward direction of time is spinning. This is Einstein’s curvature in the forward direction of time. Herein, the basis is outlined for time dilation cosmology in a spacetime/quantum continuum, including the time dilation-based derivation of the mass of the Cosmic Microwave Background Radiation (CMBR), and time dilation formulas are derived for stellar system orbital, and galactic rotation, velocities, the force in time in Newtons, the Hamiltonian, the Hubble shift, the empirical gravitational constant, G, and other formulas, showing their direct relationship to the difference in the rate of time between the far distant observer’s invariant 1 s/s rate of time and the slower rate of time at the coordinate point, proving the universe is not composed of separate bodies moving through space, but is an evolving 3-dimensional holographic continuum containing varying densities evolving forward in the forward direction of time, the 4th dimension, at apparently different rates of time, the velocities merely being compensation for those slower rates of time in a continuum evolving forward overall at c, which is why light propagates at c, even from a moving source. As per General Relativity, if there is no rate of time difference between coordinate points, there is no gravitational attraction between those points, and no gravitationally induced velocity. This model resolves all the major conundrums in astrophysics, eliminating Dark Energy and Dark Matter, and ties astrophysics directly to quantum physics.展开更多
Is it possible that the current cosmic accelerating expansion will turn into a decelerating one？ Can this transition be realized by some viable theoretical model that is consistent with the standard Big Bang cosmolog...Is it possible that the current cosmic accelerating expansion will turn into a decelerating one？ Can this transition be realized by some viable theoretical model that is consistent with the standard Big Bang cosmology？ We study a class of phenomeno- logical models with a transient acceleration, based on a dynamical dark energy with a very general form of equation of state Pde = αPde -- βpdem. It mimics the cosmolog- ical constant αde → const for a small scale factor a, and behaves as a barotropic gas with pde → α-3（α＋1） with α 〉 0 for large a. The cosmic evolution of four models in the class has been examined in detail, and all yield a smooth transient acceleration. Depending on the specific model, the future universe may be dominated by either dark energy or by matter. In two models, the dynamical dark energy can be explicitly real- ized by a scalar field with an analytical potential V（O）. Moreover, a statistical analysis shows that the models can be as robust as ACDM in confronting the observational data of Type Ia supernovae, cosmic microwave background （CMB） and baryon acoustic os- cillation. As improvements over previous studies, our models overcome the problem of over-abundance of dark energy during early eras, and satisfy the constraints on dark energy from WMAP observations of CMB.展开更多
This paper is a further elaboration of the author’s Time Dilation Cosmology (TDC) holographic model that ties gravitation and celestial mechanics and kinematics directly to time dilation, resolving all the major conu...This paper is a further elaboration of the author’s Time Dilation Cosmology (TDC) holographic model that ties gravitation and celestial mechanics and kinematics directly to time dilation, resolving all the major conundrums in astrophysics, and ties astrophysics directly to quantum physics. It begins with a brief summary of the TDC model and contains the new derivation for the time dilation version of the formula for summing relativistic velocities, Einstein’s gravitational constant and the time dilation versions for the Lorentz factor and the Euclidean norm of the 3d velocity vector, the two of which can then be used in the Four-velocity formula. It is demonstrated how orbital curvature is manifested as the resultant of two time dilation-manifested velocities. It also explains why an interferometer cannot distinguish free fall from zero gravity and further elaborates on the author’s previous explanations of how spiral galaxies are formed, and contains mathematical proof that Black Holes are actually Magnetospheric Eternally Collapsing Objects (MECOs) that are massless spacetime vortices.展开更多
This is the fifth paper in a series on Time Dilation Cosmology, TDC. TDC is an eternal holographic model of the universe based on time dilation that ties astrophysics to quantum physics and resolves all the conundrums...This is the fifth paper in a series on Time Dilation Cosmology, TDC. TDC is an eternal holographic model of the universe based on time dilation that ties astrophysics to quantum physics and resolves all the conundrums in astrophysics and serves as a model for the unified field. In the author’s previous four TDC papers, it was demonstrated that all gravitationally induced velocities are compensation for the apparent difference in the rates of time, “dRt”, due to mass/energy densities, and, vice-versa, in all force-induced velocities the dRt is compensation for the velocity, so the uniform evolution of the continuum at c is maintained at the invariant 1 s/s rate of time of the universe as a whole. These compensations make it impossible for an event to lag behind or get ahead of the evolving continuum. When the author did the first velocity formula derivations in “General Relativity: Effects in Time as Causation” [1], the author felt the explanations for the appearance of the 2spatial and the 3temporal acceleration factors in the formulas were correct, but poorly explained and incomplete. This paper is a proof of the temporal and spatial acceleration factors used in the time dilation-based velocity formula derivations in the Time Dilation Cosmology model.展开更多
Recently proposed two swampland criteria that arising from string theory landscape leads to the important challenge of the realization of single-field inflationary models. Especially one of swampland criteria which im...Recently proposed two swampland criteria that arising from string theory landscape leads to the important challenge of the realization of single-field inflationary models. Especially one of swampland criteria which implies a large tensor-to-scalar ratio is strongly in tension with recent observational results. In this paper, we explore the possibility the swampland conjectures could be compatible with single-field inflationary scenarios if the effects due to the quantum theory of gravity are considered. We show that the quantum gravitational effects due to the nonlinear dispersion relation provides significant modifications on the amplitude of both the scalar and tensor perturbation spectra. Such modifications could be either raise or reduce the perturbation spectra depending on the values of the parameters in the nonlinear terms of the dispersion relations. Therefore, these effects can reduce the tensor-to-scalar ratio to a smaller value, which helps to relax the tension between the swampland conjecture and observational data.展开更多
This research paper examines a cosmological model in flat space-time via f(R,G)gravity,where R and G are the Ricci scalar and Gauss-Bonnet invariant,respectively.Our model assumes that f(R,G)is an exponential function...This research paper examines a cosmological model in flat space-time via f(R,G)gravity,where R and G are the Ricci scalar and Gauss-Bonnet invariant,respectively.Our model assumes that f(R,G)is an exponential function of G combined with a linear combination of R.We scrutinize the observational limitations under a power law cosmology that relies on two parameters,the Hubble constant(Ho)and the deceleration parameter(q)utilizing the 57-point H(z)data,8-point BAO data,1701-point Pantheon+data,joint data of H(z)+Pantheon,and joint data of H(z)+BAO+Pantheon+.The outcomes for H_(0)and q are realistic within observational ranges.We also address energy conditions,Om(z)analysis,and cosmographical parameters such as jerk,lerk,and snap.Our estimate of Ho is remarkably consistent with various recent Planck Collaboration studies that utilize the ACDM model.According to our study,power law cosmology within the context of f(R,G)gravity provides the most comprehensive explanation of the important aspects of cosmic evolution.展开更多
The China Space Station Telescope(CSST)is the next-generation Stage IV survey telescope.It can simultaneously perform multiband imaging and slitless spectroscopic wide-and deep-field surveys in ten years and an ultra-...The China Space Station Telescope(CSST)is the next-generation Stage IV survey telescope.It can simultaneously perform multiband imaging and slitless spectroscopic wide-and deep-field surveys in ten years and an ultra-deep field(UDF)survey in two years,which are suitable for cosmological studies.Here we review several CSST cosmological probes,such as weak gravitational lensing,two-dimensional(2D)and three-dimensional(3D)galaxy clustering,galaxy cluster abundance,cosmic void,Type Ia supernovae(SNe Ia),and baryonic acoustic oscillations(BAO),and explore their capabilities and prospects in discovering new physics and opportunities in cosmology.We find that CSST will measure the matter distribution from small to large scales and the expansion history of the Universe with extremely high accuracy,which can provide percent-level stringent constraints on the property of dark energy and dark matter and precisely test the theories of gravity.展开更多
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
In this paper,we study the dynamics of k-essence in loop quantum cosmology(LQC).The study indicates that the loop quantum gravity(LQG)effect plays a key role only in the early epoch of the universe and is diluted in t...In this paper,we study the dynamics of k-essence in loop quantum cosmology(LQC).The study indicates that the loop quantum gravity(LQG)effect plays a key role only in the early epoch of the universe and is diluted in the later stages.The fixed points in LQC are basically consistent with those in standard Friedmann-Robertson-Walker(FRW)cosmology.For most of the attractor solutions,the stability conditions in L Q C are in agreement with those for the standard FRW universe.For some special fixed points,however,tighter constraints are imposed thanks to the LQG effect.展开更多
We in this paper study a class of mechanism of the production of the primordial magnetic field(PMF) in the non-singular bouncing cosmology, through the coupling of the electromagnetic field to gravity. We adopt an ele...We in this paper study a class of mechanism of the production of the primordial magnetic field(PMF) in the non-singular bouncing cosmology, through the coupling of the electromagnetic field to gravity. We adopt an electrodynamic model with a coupling coefficient as a function of the scale factor a, i.e., f = 1 +(a/a?)^(-n), with a? and n > 0 being constants. With analytical calculations, we find that this model can yield a blue tilted power spectrum of PMF on large scales from 1 Mpc to the Hubble length if the bounce scenario has experienced a contracting phase with an equation-of-state parameter larger than-1/3. Furthermore, in order to satisfy the constraints of observational data, the present mechanism favors the so-called ekpyrotic-bounce paradigm. The back-reaction of the energy density of PMF at the bouncing point can lead to additional theoretical constraints on the underlying bouncing paradigm.展开更多
We present a forecast of the cosmological parameter estimation using fast radio bursts(FRBs)from the upcoming Square Kilometre Array(SKA),focusing on the issues of dark energy,the Hubble constant,and baryon density.We...We present a forecast of the cosmological parameter estimation using fast radio bursts(FRBs)from the upcoming Square Kilometre Array(SKA),focusing on the issues of dark energy,the Hubble constant,and baryon density.We simulate 105and 106localized FRBs from a 10-year SKA observation,and find that:(1)using 106FRB data alone can tightly constrain dark-energy equation of state parameters better than CMB+BAO+SNe,providing an independent cosmological probe to explore dark energy;(2)combining the FRB data with gravitational-wave standard siren data from 10-year observation with the Einstein Telescope,the Hubble constant can be constrained to a sub-percent level,serving as a powerful low-redshift probe;(3)using 106FRB data can constrain the baryon density?bh to a precision of~0.1%.Our results indicate that SKA-era FRBs will provide precise cosmological measurements to shed light on both dark energy and the missing baryon problem,and help resolve the Hubble tension.展开更多
We reconstruct the cosmological background evolution under the scenario of dynamical dark energy through the Gaussian process approach,using the latest Dark Energy Spectroscopic Instrument(DESI)baryon acoustic oscilla...We reconstruct the cosmological background evolution under the scenario of dynamical dark energy through the Gaussian process approach,using the latest Dark Energy Spectroscopic Instrument(DESI)baryon acoustic oscillations(BAO)combined with other observations.Our results reveal that the reconstructed dark-energy equation-of-state(EoS)parameter w(z)exhibits the so-called quintom-B behavior,crossing-1 from phantom to quintessence regime as the universe expands.We investigate under what situation this type of evolution could be achieved from the perspectives of field theories and modified gravity.In particular,we reconstruct the corresponding actions for f(R),f(T),and f(Q)gravity,respectively.We explicitly show that,certain modified gravity can exhibit the quintom dynamics and fit the recent DESI data efficiently,and for all cases the quadratic deviation from theΛCDM scenario is mildly favored.展开更多
We explore the feasibility of H I galaxy redshift surveys with the Five-hundred-meter Aperture Spherical Telescope(FAST) and its proposed Core Array interferometry.Using semi-analytical simulations,we compare the perf...We explore the feasibility of H I galaxy redshift surveys with the Five-hundred-meter Aperture Spherical Telescope(FAST) and its proposed Core Array interferometry.Using semi-analytical simulations,we compare the performance of the FAST single-dish and Core Array modes in drift scan (DS) and on-the-fly (OTF) observations across different redshifts.Our results show that the FAST single-dish mode enables significant H I detections at low redshifts (z■0.35) but is limited at higher redshifts due to shot noise.The Core Array interferometry,with higher sensitivity and angular resolution,provides robust H I galaxy detections up to z~1,maintaining a sufficient number density for power spectrum measurements and BAO constraints.At low redshifts (z~0.01–0.08),both configurations perform well,though cosmic variance dominates uncertainties.At higher redshifts (z>0.35),the Core Array outperforms the single-dish mode,while increasing the survey area has little impact on single-dish observations due to shot noise limitations.The DS mode efficiently covers large sky areas but is constrained by Earth’s rotation,whereas the OTF mode allows more flexible deep-field surveys at the cost of operational overhead.Our findings highlight the importance of optimizing survey strategies to maximize FAST’s potential for H I cosmology.The Core Array is particularly well-suited for high-redshift H I galaxy surveys,enabling precise constraints on large-scale structure and dark energy.展开更多
In a previous paper, we suggested a possible theory to unify Dirac cosmology and general relativity without introducing two time-scale hypothesis. The zeroth and the first order approximations in our theory yield the ...In a previous paper, we suggested a possible theory to unify Dirac cosmology and general relativity without introducing two time-scale hypothesis. The zeroth and the first order approximations in our theory yield the Einstein field equations, and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
Since the large-number hypothesis was proposed by Dirac in 1937, a number of comsology models with a varying constant of gravitation have been suggested, but most of them met with difficulties in varying degrees. Espe...Since the large-number hypothesis was proposed by Dirac in 1937, a number of comsology models with a varying constant of gravitation have been suggested, but most of them met with difficulties in varying degrees. Especially, except the Canuto et al. scalar covariant theory, they can not explain the contradictions between Einstein’s general relativity and Dirac cosmology. But unfortunately,展开更多
The accelerated expansion of the Universe has sparked significant interest in the mysterious concept of dark energy within cosmology.Various theories have been proposed to explain dark energy,and many models have been...The accelerated expansion of the Universe has sparked significant interest in the mysterious concept of dark energy within cosmology.Various theories have been proposed to explain dark energy,and many models have been developed to understand its origins and properties.This research explores cosmic expansion using the Polytropic Gas(PG)approach,which combines Dark Matter(DM)and Dark Energy(DE)into a single mysterious fluid.We used the principles of general relativity and built our model within the homogeneous and isotropic framework of Friedmann-Lemaître-Robertson-Walker(FLRW)spacetime.We revised the Original Polytropic Gas(OPG)model to expand its applicability beyond the OPG,to theΛCDM model.Our model's parameters were carefully adjusted to reflect key cosmological features of the variable PG approach.To validate our model,we performed a Markov chain Monte Carlo analysis using recent Supernova data from the Pantheon+survey,36 observational data points,162 Gamma-Ray Bursts,and 24 binned Quasars distance modulus data.The AIC and BIC criteria indicate that our model is slightly preferred over theΛCDM model based on observational data.We also tested our model with data,Supernova,Gamma-Ray Bursts,and Quasars and found that it exhibits a transition from a quintessential to phantom regime.The Polytropic dark fluid model(PDFM)is a promising candidate that effectively addresses the interplay between cosmic acceleration and dark energy.展开更多
基金Supported in part by the National Natural Science Foundation of China(NNSCF)under Grant Nos.11375153 and 11675145T.Z.is supported in part by NFSC under Grant No.11675143the Fundamental Research Funds for the Provincial Universities of Zhejiang in China under Grant No.RF-A2019015
文摘Recently the background independent nonperturbative quantization has been extended to various theories of gravity and the corresponding quantum effective cosmology has been derived, which provides us with necessary avenue to explore the pre-inflationary dynamics. Brans-Dicke(BD) loop quantum cosmology(LQC) is one of such theories whose effective background dynamics is considered in this article. Starting with a quantum bounce, we explore the pre-inflationary dynamics of a universe sourced by a scalar field with the Starobinsky potential in BD-LQC. Our study is based on the idea that though Einstein’s and Jordan’s frames are classically equivalent up to a conformal transformation in BD theory, this is no longer true after quantization. Taking the Jordan frame as the physical one we explore in detail the bouncing scenario which is followed by a phase of a slow roll inflation. The three phases of the evolution of the universe, namely, bouncing, transition from quantum bounce to classical universe, and the slow roll inflation, are noted for an initially kinetic energy dominated bounce. In addition, to be consistent with observations, we also identify the allowed phase space of initial conditions that would produce at least 60 e-folds of expansion during the slow roll inflation.
基金supported by the Chinese Scholarship CouncilSTFC+6 种基金supported by NSFC grants 11925303,11720101004 and 11890691supported by NSFC Grant 11890691by the Youth Innovation Promotion Association CASby the Nebula Talents Program of NAOCsupported by the National Key Basic Research and Development Program of Chinaa grant of CAS Interdisciplinary Innovation Teamthe science research grants from the China Manned Space Project with No.CMS-CSST-2021-B01。
文摘We propose a new consistency test for theΛCDM cosmology using baryonic acoustic oscillations(BAO)and redshift space distortion(RSD)measurements from galaxy redshift surveys.Specifically,we determine the peak position of fσ8(z)in redshift z offered by an RSD measurement,and compare it to the one predicted by the BAO observables assuming a flatΛCDM cosmology.We demonstrate this new test using the simulated data for the DESI galaxy survey,and argue that this test complements those using the background observables alone,and is less subject to systematics in the RSD analysis,compared to traditional methods using values of fσ8(z)directly.
文摘This model ties gravitation and celestial mechanics and kinematics directly to time dilation. It is a new theory of cosmology and the evolution of galaxies. Space and time are not two separate things, but two aspects of a single thing, “spacetime”. Whatever affects space, affects time, and vice-versa. If time speeds up, space must contract to maintain the speed of light, c, and when space thickens into a mass, it is harder to evolve forward, and time appears to slow. If spatial events are spinning as time passes, then the forward direction of time is spinning. This is Einstein’s curvature in the forward direction of time. Herein, the basis is outlined for time dilation cosmology in a spacetime/quantum continuum, including the time dilation-based derivation of the mass of the Cosmic Microwave Background Radiation (CMBR), and time dilation formulas are derived for stellar system orbital, and galactic rotation, velocities, the force in time in Newtons, the Hamiltonian, the Hubble shift, the empirical gravitational constant, G, and other formulas, showing their direct relationship to the difference in the rate of time between the far distant observer’s invariant 1 s/s rate of time and the slower rate of time at the coordinate point, proving the universe is not composed of separate bodies moving through space, but is an evolving 3-dimensional holographic continuum containing varying densities evolving forward in the forward direction of time, the 4th dimension, at apparently different rates of time, the velocities merely being compensation for those slower rates of time in a continuum evolving forward overall at c, which is why light propagates at c, even from a moving source. As per General Relativity, if there is no rate of time difference between coordinate points, there is no gravitational attraction between those points, and no gravitationally induced velocity. This model resolves all the major conundrums in astrophysics, eliminating Dark Energy and Dark Matter, and ties astrophysics directly to quantum physics.
基金Supported by the National Natural Science Foundation of China
文摘Is it possible that the current cosmic accelerating expansion will turn into a decelerating one？ Can this transition be realized by some viable theoretical model that is consistent with the standard Big Bang cosmology？ We study a class of phenomeno- logical models with a transient acceleration, based on a dynamical dark energy with a very general form of equation of state Pde = αPde -- βpdem. It mimics the cosmolog- ical constant αde → const for a small scale factor a, and behaves as a barotropic gas with pde → α-3（α＋1） with α 〉 0 for large a. The cosmic evolution of four models in the class has been examined in detail, and all yield a smooth transient acceleration. Depending on the specific model, the future universe may be dominated by either dark energy or by matter. In two models, the dynamical dark energy can be explicitly real- ized by a scalar field with an analytical potential V（O）. Moreover, a statistical analysis shows that the models can be as robust as ACDM in confronting the observational data of Type Ia supernovae, cosmic microwave background （CMB） and baryon acoustic os- cillation. As improvements over previous studies, our models overcome the problem of over-abundance of dark energy during early eras, and satisfy the constraints on dark energy from WMAP observations of CMB.
文摘This paper is a further elaboration of the author’s Time Dilation Cosmology (TDC) holographic model that ties gravitation and celestial mechanics and kinematics directly to time dilation, resolving all the major conundrums in astrophysics, and ties astrophysics directly to quantum physics. It begins with a brief summary of the TDC model and contains the new derivation for the time dilation version of the formula for summing relativistic velocities, Einstein’s gravitational constant and the time dilation versions for the Lorentz factor and the Euclidean norm of the 3d velocity vector, the two of which can then be used in the Four-velocity formula. It is demonstrated how orbital curvature is manifested as the resultant of two time dilation-manifested velocities. It also explains why an interferometer cannot distinguish free fall from zero gravity and further elaborates on the author’s previous explanations of how spiral galaxies are formed, and contains mathematical proof that Black Holes are actually Magnetospheric Eternally Collapsing Objects (MECOs) that are massless spacetime vortices.
文摘This is the fifth paper in a series on Time Dilation Cosmology, TDC. TDC is an eternal holographic model of the universe based on time dilation that ties astrophysics to quantum physics and resolves all the conundrums in astrophysics and serves as a model for the unified field. In the author’s previous four TDC papers, it was demonstrated that all gravitationally induced velocities are compensation for the apparent difference in the rates of time, “dRt”, due to mass/energy densities, and, vice-versa, in all force-induced velocities the dRt is compensation for the velocity, so the uniform evolution of the continuum at c is maintained at the invariant 1 s/s rate of time of the universe as a whole. These compensations make it impossible for an event to lag behind or get ahead of the evolving continuum. When the author did the first velocity formula derivations in “General Relativity: Effects in Time as Causation” [1], the author felt the explanations for the appearance of the 2spatial and the 3temporal acceleration factors in the formulas were correct, but poorly explained and incomplete. This paper is a proof of the temporal and spatial acceleration factors used in the time dilation-based velocity formula derivations in the Time Dilation Cosmology model.
基金Supported by National Natural Science Foundation of China under Grant No.11675143the Fundamental Research for the Provincial Universities of Zhejiang in China under Grant No.RF-A2019015
文摘Recently proposed two swampland criteria that arising from string theory landscape leads to the important challenge of the realization of single-field inflationary models. Especially one of swampland criteria which implies a large tensor-to-scalar ratio is strongly in tension with recent observational results. In this paper, we explore the possibility the swampland conjectures could be compatible with single-field inflationary scenarios if the effects due to the quantum theory of gravity are considered. We show that the quantum gravitational effects due to the nonlinear dispersion relation provides significant modifications on the amplitude of both the scalar and tensor perturbation spectra. Such modifications could be either raise or reduce the perturbation spectra depending on the values of the parameters in the nonlinear terms of the dispersion relations. Therefore, these effects can reduce the tensor-to-scalar ratio to a smaller value, which helps to relax the tension between the swampland conjecture and observational data.
基金support of the Ministry of Science and Higher Education of the Russian Federation(State contract GZ0110/23-10-IF)。
文摘This research paper examines a cosmological model in flat space-time via f(R,G)gravity,where R and G are the Ricci scalar and Gauss-Bonnet invariant,respectively.Our model assumes that f(R,G)is an exponential function of G combined with a linear combination of R.We scrutinize the observational limitations under a power law cosmology that relies on two parameters,the Hubble constant(Ho)and the deceleration parameter(q)utilizing the 57-point H(z)data,8-point BAO data,1701-point Pantheon+data,joint data of H(z)+Pantheon,and joint data of H(z)+BAO+Pantheon+.The outcomes for H_(0)and q are realistic within observational ranges.We also address energy conditions,Om(z)analysis,and cosmographical parameters such as jerk,lerk,and snap.Our estimate of Ho is remarkably consistent with various recent Planck Collaboration studies that utilize the ACDM model.According to our study,power law cosmology within the context of f(R,G)gravity provides the most comprehensive explanation of the important aspects of cosmic evolution.
基金the support of the National Key R&D Program of China(Grant Nos.2022YFF0503404,and 2020SKA0110402)the CAS Project for Young Scientists in Basic Research(Grant No.YSBR092)+4 种基金the support of the National Natural Science Foundation of China(Grant No.12361141814)the Chinese Academy of Sciences(Grant No.ZDKYYQ20200008)the support of the National Natural Science Foundation of China(Grant No.12133006)the National Key R&D Program of China(Grant Nos.2023YFA1607800,and 2023YFA1607801)supported by the Science Research grants from the China Manned Space Project(Grant Nos.CMS-CSST-2021-B01,CMS-CSST-2021-A01,and CMS-CSST-2021A03)。
文摘The China Space Station Telescope(CSST)is the next-generation Stage IV survey telescope.It can simultaneously perform multiband imaging and slitless spectroscopic wide-and deep-field surveys in ten years and an ultra-deep field(UDF)survey in two years,which are suitable for cosmological studies.Here we review several CSST cosmological probes,such as weak gravitational lensing,two-dimensional(2D)and three-dimensional(3D)galaxy clustering,galaxy cluster abundance,cosmic void,Type Ia supernovae(SNe Ia),and baryonic acoustic oscillations(BAO),and explore their capabilities and prospects in discovering new physics and opportunities in cosmology.We find that CSST will measure the matter distribution from small to large scales and the expansion history of the Universe with extremely high accuracy,which can provide percent-level stringent constraints on the property of dark energy and dark matter and precisely test the theories of gravity.
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 the Natural Science Foundation of China(11775036)Fok Ying Tung Education Foundation(171006)Jian-Pin Wu is also supported by Top Talent Support Program from Yangzhou University.
文摘In this paper,we study the dynamics of k-essence in loop quantum cosmology(LQC).The study indicates that the loop quantum gravity(LQG)effect plays a key role only in the early epoch of the universe and is diluted in the later stages.The fixed points in LQC are basically consistent with those in standard Friedmann-Robertson-Walker(FRW)cosmology.For most of the attractor solutions,the stability conditions in L Q C are in agreement with those for the standard FRW universe.For some special fixed points,however,tighter constraints are imposed thanks to the LQG effect.
基金supported by the National Natural Science Foundation of China for Fostering Talents in Basic Science (Grant No. J1310021)the National Natural Science Foundation of China (Grant Nos. 11653002, 11722327, and 11421303)+1 种基金the China Academy of Space Technology (CAST) Young Elite Scientists Sponsorship Program (Grant No. 2016QNRC001)the Fundamental Research Funds for the Central Universities
文摘We in this paper study a class of mechanism of the production of the primordial magnetic field(PMF) in the non-singular bouncing cosmology, through the coupling of the electromagnetic field to gravity. We adopt an electrodynamic model with a coupling coefficient as a function of the scale factor a, i.e., f = 1 +(a/a?)^(-n), with a? and n > 0 being constants. With analytical calculations, we find that this model can yield a blue tilted power spectrum of PMF on large scales from 1 Mpc to the Hubble length if the bounce scenario has experienced a contracting phase with an equation-of-state parameter larger than-1/3. Furthermore, in order to satisfy the constraints of observational data, the present mechanism favors the so-called ekpyrotic-bounce paradigm. The back-reaction of the energy density of PMF at the bouncing point can lead to additional theoretical constraints on the underlying bouncing paradigm.
基金supported by the National SKA Program of China(Grant Nos.2022SKA01102002022SKA0110203)+1 种基金the National Natural Science Foundation of China(Grant Nos.11975072,11835009,11875102,and 11988101)the National 111 Project of China(Grant No.B16009)。
文摘We present a forecast of the cosmological parameter estimation using fast radio bursts(FRBs)from the upcoming Square Kilometre Array(SKA),focusing on the issues of dark energy,the Hubble constant,and baryon density.We simulate 105and 106localized FRBs from a 10-year SKA observation,and find that:(1)using 106FRB data alone can tightly constrain dark-energy equation of state parameters better than CMB+BAO+SNe,providing an independent cosmological probe to explore dark energy;(2)combining the FRB data with gravitational-wave standard siren data from 10-year observation with the Einstein Telescope,the Hubble constant can be constrained to a sub-percent level,serving as a powerful low-redshift probe;(3)using 106FRB data can constrain the baryon density?bh to a precision of~0.1%.Our results indicate that SKA-era FRBs will provide precise cosmological measurements to shed light on both dark energy and the missing baryon problem,and help resolve the Hubble tension.
基金National Key Research and Development Program of China(2021YFC2203100)National Natural Science Foundation of China(12261131497 and 12003029)+2 种基金CAS young interdisciplinary innovation team(JCTD2022-20)111 Project(B23042)USTC Fellowship for International Cooperation,and USTC Research Funds of the Double First-Class Initiative。
文摘We reconstruct the cosmological background evolution under the scenario of dynamical dark energy through the Gaussian process approach,using the latest Dark Energy Spectroscopic Instrument(DESI)baryon acoustic oscillations(BAO)combined with other observations.Our results reveal that the reconstructed dark-energy equation-of-state(EoS)parameter w(z)exhibits the so-called quintom-B behavior,crossing-1 from phantom to quintessence regime as the universe expands.We investigate under what situation this type of evolution could be achieved from the perspectives of field theories and modified gravity.In particular,we reconstruct the corresponding actions for f(R),f(T),and f(Q)gravity,respectively.We explicitly show that,certain modified gravity can exhibit the quintom dynamics and fit the recent DESI data efficiently,and for all cases the quadratic deviation from theΛCDM scenario is mildly favored.
基金the support of the National SKA Program of China (Nos.2022SKA0110200 and 2022SKA0110203)the National Natural Science Foundation of China (NSFC,Nos.12473091 and 12473001),and 111 Project (No.B16009)the support of the Fundamental Research Funds for the Central Universities (No.N2405008)。
文摘We explore the feasibility of H I galaxy redshift surveys with the Five-hundred-meter Aperture Spherical Telescope(FAST) and its proposed Core Array interferometry.Using semi-analytical simulations,we compare the performance of the FAST single-dish and Core Array modes in drift scan (DS) and on-the-fly (OTF) observations across different redshifts.Our results show that the FAST single-dish mode enables significant H I detections at low redshifts (z■0.35) but is limited at higher redshifts due to shot noise.The Core Array interferometry,with higher sensitivity and angular resolution,provides robust H I galaxy detections up to z~1,maintaining a sufficient number density for power spectrum measurements and BAO constraints.At low redshifts (z~0.01–0.08),both configurations perform well,though cosmic variance dominates uncertainties.At higher redshifts (z>0.35),the Core Array outperforms the single-dish mode,while increasing the survey area has little impact on single-dish observations due to shot noise limitations.The DS mode efficiently covers large sky areas but is constrained by Earth’s rotation,whereas the OTF mode allows more flexible deep-field surveys at the cost of operational overhead.Our findings highlight the importance of optimizing survey strategies to maximize FAST’s potential for H I cosmology.The Core Array is particularly well-suited for high-redshift H I galaxy surveys,enabling precise constraints on large-scale structure and dark energy.
文摘In a previous paper, we suggested a possible theory to unify Dirac cosmology and general relativity without introducing two time-scale hypothesis. The zeroth and the first order approximations in our theory yield the Einstein field equations, and
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Since the large-number hypothesis was proposed by Dirac in 1937, a number of comsology models with a varying constant of gravitation have been suggested, but most of them met with difficulties in varying degrees. Especially, except the Canuto et al. scalar covariant theory, they can not explain the contradictions between Einstein’s general relativity and Dirac cosmology. But unfortunately,
文摘The accelerated expansion of the Universe has sparked significant interest in the mysterious concept of dark energy within cosmology.Various theories have been proposed to explain dark energy,and many models have been developed to understand its origins and properties.This research explores cosmic expansion using the Polytropic Gas(PG)approach,which combines Dark Matter(DM)and Dark Energy(DE)into a single mysterious fluid.We used the principles of general relativity and built our model within the homogeneous and isotropic framework of Friedmann-Lemaître-Robertson-Walker(FLRW)spacetime.We revised the Original Polytropic Gas(OPG)model to expand its applicability beyond the OPG,to theΛCDM model.Our model's parameters were carefully adjusted to reflect key cosmological features of the variable PG approach.To validate our model,we performed a Markov chain Monte Carlo analysis using recent Supernova data from the Pantheon+survey,36 observational data points,162 Gamma-Ray Bursts,and 24 binned Quasars distance modulus data.The AIC and BIC criteria indicate that our model is slightly preferred over theΛCDM model based on observational data.We also tested our model with data,Supernova,Gamma-Ray Bursts,and Quasars and found that it exhibits a transition from a quintessential to phantom regime.The Polytropic dark fluid model(PDFM)is a promising candidate that effectively addresses the interplay between cosmic acceleration and dark energy.
