The Evolving Absolute Magnitude of Type 1a Supernovae and Its Critical Impact on the Cosmological Parameters

In this work, a computer optimization model has been developed that allows one to load the initial data of observations of supernovae 1a into a table and, in simple steps, by searching for the best fit between observations and theory, obtain the values of the parameters of cosmological models. The optimization is carried out assuming that the absolute magnitude of supernovae is not constant, but evolves with time. It is assumed that the dependence of the absolute magnitude on the redshift is linear: M = M( z = 0) + εc z, where εc is the evolution coefficient of the absolute magnitude of type 1a supernovae. In the case of a flat universe ( ΩM + ΩΛ = 1 ), the best fit between theory and observation is εc = 0.304. In this case, for the cosmological parameters we obtain ΩΛ = 0.000, ΩM =1.000. Naturally, this result exactly coincides with the simulation result for the model with zero cosmological constant ( εc = 0.304, q0 = 0.500 ). Within the framework of the ΛCDM model, without restriction on space curvature ( ΩM + ΩΛ+ ΩK = 1 ), we obtain the following values: εc = 0.304, ΩΛ = 0.000, ΩM = 1.000, ΩK =0.000. Those, this case also leads to a flat model of the Universe ( ΩK =0.000 ). In this work, the critical influence of the absolute magnitude M of type 1a supernovae on the cosmological parameters is also shown. In particular, it was found that a change in this value by only 0.4m (from -19.11 to -18.71) leads to a change in the parameters from ΩΛ = 0.7 and ΩM = 0.3 to ΩΛ = 0 and ΩM =1.

Combining optical and X-ray observations of galaxy clusters to constrain cosmological parameters

Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clusters lie between 0.1 and 0.6,and the redshift range of their arcs is from 0.4 to 4.9.These clusters are selected carefully from strong gravitational lensing systems which have both X-ray satellite observations and optical giant luminous arcs with known redshifts.Giant arcs usually appear in the central region of clusters,where mass can be traced with luminosity quite well.Based on gravitational lensing theory and a cluster mass distribution model,we can derive a ratio using two angular diameter distances.One is the distance between lensing sources and the other is that between the deflector and the source. Since angular diameter distance relies heavily on cosmological geometry,we can use these ratios to constrain cosmological models.Moreover,X-ray gas fractions of galaxy clusters can also be a cosmological probe.Because there are a dozen parameters to be fitted,we introduce a new analytic algorithm,Powell＇s UOBYQA（Unconstrained Optimization By Quadratic Approximation） ,to accelerate our calculation.Our result demonstrates that this algorithm is an effective fitting method for such a continuous multi-parameter constraint.We find an interesting fact that these two approaches are separately sensitive toΩΛandΩM.By combining them,we can get reasonable fitting values of basic cosmological parameters：ΩM=0.26 ＋0.04 -0.04,andΩΛ=0.82 ＋0.14 -0.16.

Cosmological parameters for spatially flat dust filled Universe in Brans-Dicke theory

We have investigated late time acceleration for a spatially fiat dust filled Universe in Brans- Dicke theory in the presence of a positive cosmological constant A. Expressions for Hubble＇s constant, luminosity distance and apparent magnitude have been obtained for our model. The theoretical results are compared with observed values of the latest 287 high redshift （0.3 ≤ z ≤1.4） Type Ia supernova data taken from the Union 2.1 compilation to estimate present values of matter and dark energy parame- ters, （Ωm）0 and （ΩA）0. We have also estimated the present value of Hubble＇s constant H0 in light of an updated sample of Hubble parameter measurements including 19 independent data points. The results are found to be in good agreement with recent astrophysical observations. We also calculated various physical parameters such as matter and dark energy densities, present age of the Universe and decelera- tion parameter. The value for Brans-Dicke-coupling constant ω is set to be 40 000 based on accuracy of solar system tests and recent experimental evidence.

Joint constraints on cosmological parameters using future multi-band gravitational wave standard siren observations

Gravitational waves(GWs)from compact binary coalescences can be used as standard sirens to explore the cosmic expansion history.In the next decades,it is anticipated that we could obtain the multi-band GW standard siren data(from nanohertz to a few hundred hertz),which are expected to play an important role in cosmological parameter estimation.In this work,we provide,for the first time to the best of our knowledge,joint constraints on cosmological parameters using the future multi-band GW standard siren observations.We simulate the multi-band GW standard sirens based on the SKA-era pulsar timing array(PTA),Taiji observatory,and Cosmic Explorer(CE)to perform cosmological analysis.In theΛCDM model,we find that the joint PTA+Taiji+CE data could provide a tight constraint on the Hubble constant with a 0.5%precision.Moreover,PTA+Taiji+CE could break the cosmological parameter degeneracies generated by CMB,especially in the dynamical dark energy models.When combining the PTA+Taiji+CE data with the CMB data,the constraint precisions of?_(m)and H_(0)are 1.0%and 0.3%,respectively,meeting the standard of precision cosmology.The joint CMB+PTA+Taiji+CE data giveσ(_(w))=0.028 in the wCDM model andσ(w_(0))=0.11 andσ(w_(a))=0.32 in the w_(0)w_(a)CDM model,which are comparable with or close to the latest constraint results by CMB+BAO+SN.In conclusion,the future multi-band GW observations are expected to be used for exploring the nature of dark energy and measuring the Hubble constant.

Cosmological Constraints on Neutrino Masses in Light of JWST Red and Massive Candidate Galaxies

The overabundance of the red and massive candidate galaxies observed by the James Webb Space Telescope(JWST)implies efficient structure formation or large star formation efficiency at high redshift z~10.In the scenario of a low or moderate star formation efficiency,because massive neutrinos tend to suppress the growth of structure of the universe,the JWST observation tightens the upper bound of the neutrino masses.Assuming A cold dark matter cosmology and a star formation efficiency∈[0.05,0.3](flat prior),we perform joint analyses of Planck+JWST and Planck+BAO+JWST,and obtain improved constraints∑m_(ν)<0.196 eV and ∑m_(ν)+<0.111 eV at 95% confidence level,respectively.Based on the above assumptions,the inverted mass ordering,which implies ∑m_(ν)≥0.1 eV,is excluded by Planck+BAO+JWST at 92.7% confidence level.

Quantifying the Tension between Cosmological Models and JWST Red Candidate Massive Galaxies

We develop a Python tool to estimate the tail distribution of the number of dark matter halos beyond a mass threshold and in a given volume in a light-cone.The code is based on the extended Press-Schechter model and is computationally efficient,typically taking a few seconds on a personal laptop for a given set of cosmological parameters.The high efficiency of the code allows a quick estimation of the tension between cosmological models and the red candidate massive galaxies released by the James Webb Space Telescope,as well as scanning the theory space with the Markov Chain Monte Carlo method.As an example application,we use the tool to study the cosmological implication of the candidate galaxies presented in Labbéet al.The standard Λcold dark matter(ΛCDM)model is well consistent with the data if the star formation efficiency can reach~0.3 at high redshift.For a low star formation efficiency ε~0.1,theΛCDM model is disfavored at~2σ-3σconfidence level.

Prospects of the Multi-channel Photometric Survey Telescope in the Cosmological Application of Type Ia Supernovae

The Multi-channel Photometric Survey Telescope(Mephisto)is a real-time,three-color photometric system designed to capture the color evolution of stars and transients accurately.This telescope system can be crucial in cosmological distance measurements of low-redshift(low-z,z■0.1)Type Ia supernovae(SNe Ia).To optimize the capabilities of this instrument,we perform a comprehensive simulation study before its official operation is scheduled to start.By considering the impact of atmospheric extinction,weather conditions,and the lunar phase at the observing site involving the instrumental features,we simulate light curves of SNe Ia obtained by Mephisto.The best strategy in the case of SN Ia cosmology is to take the image at an exposure time of 130 s with a cadence of 3 days.In this condition,Mephisto can obtain hundreds of high-quality SNe Ia to achieve a distance measurement better than 4.5%.Given the on-time spectral classification and monitoring of the Lijiang 2.4 m Telescope at the same observatory,Mephisto,in the whole operation,can significantly enrich the well-calibrated sample of supernovae at low-z and improve the calibration accuracy of high-z SNe Ia.

THE COSMOLOGICAL PARAMETERS

Updated November 2013, by O. Lahav （University College London） and A.R. Liddle （University of Edinburgh）.

Dynamical Dark Energy in Light of Cosmic Distance Measurements.Ⅰ.A Demonstration Using Simulated Datasets

We develop methods to extract key dark energy information from cosmic distance measurements including the BAO scales and supernova(SN) luminosity distances.Demonstrated using simulated data sets of the complete DESI,LSST and Roman surveys designed for BAO and SN distance measurements,we show that using our method,the dynamical behavior of the energy,pressure,equation of state(with its time derivative) of dark energy and the cosmic deceleration function can all be accurately recovered from high-quality data,which allows for robust diagnostic tests for dark energy models.

Effects of the cosmological constant on chaos in an FRW scalar field universe

The dependence of chaos on two parameters of the cosmological constant and the self-interacting coefficient in the imaginary phase space for a closed Friedman- Robertson-Walker （FRW） universe with a conformally coupled scalar field, as the full understanding of the dependence in real phase space, is investigated numerically. It is found that Poincar6 plots for the two parameters less than 1 are almost the same as those in the absence of the cosmological constant and self-interacting terms. For energies below the energy threshold of 0.5 for the imaginary problem in which there are no cosmological constant and self-interacting terms, an abrupt transition to chaos occurs when at least one of the two parameters is 1. However, the strength of the chaos does not increase for energies larger than the threshold. For other situations of the two parameters larger than 1, chaos is weaker, and even disappears as the two parameters increase.

Robertson-Walker cosmological models with perfect fluid in general relativity

Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for a Robertson-Walker universe by assuming the cosmological term to be proportional to R-m（R is a scale factor and m is a constant）.A variety of solutions is presented.The physical significance of the cosmological models has also been discussed.

Bianchi type-I cosmological models with perfect fluid in general relativity

Einstein＇s field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for the Bianchi type-I universe by assuming that the cosmological term is proportional to R-m （R is a scale factor and m is a constant）.A variety of solutions are presented.The physical significance of the respective cosmological models are also discussed.

Degeneracy and discreteness in cosmological model fitting

We explore the problems of degeneracy and discreteness in the standard cosmological model（ΛCDM）. We use the Observational Hubble Data（OHD） and the type Ia supernovae（SNe Ia） data to study this issue. In order to describe the discreteness in fitting of data, we define a factor G to test the influence from each single data point and analyze the goodness of G. Our results indicate that a higher absolute value of G shows a better capability of distinguishing models, which means the parameters are restricted into smaller confidence intervals with a larger figure of merit evaluation. Consequently, we claim that the factor G is an effective way of model differentiation when using different models to fit the observational data.

Cosmological application on five-dimensional teleparallel theory equivalent to general relativity

A theory of（4＋1）-dimensional gravity has been developed on the basis of which equivalent to the theory of general relativity by teleparallel.The fundamental gravitational field variables are the 5-dimensional（5D） vector fields（pentad）,defined globally on a manifold M,and gravity is attributed to the torsion.The Lagrangian density is quadratic in the torsion tensor.We then apply the field equations to two different homogenous and isotropic geometric structures which give the same line element,i.e.,FRW in five dimensions.The cosmological parameters are calculated and some cosmological problems are discussed.

Method of determining cosmological parameter ranges with samples of candles with an intrinsic distribution

In this paper, the effect of the intrinsic distribution of cosmological candles is investigated. We find that in the case of a narrow distribution the deviation of the observed modulus of sources from the expected central value can be estimated within a ceratin range. We thus introduce lower and upper limits of X^2, X^2min and X^2max to estimate cosmological parameters by applying the conventional minimizing X^2 method. We apply this method to a gammaray burst （GRB） sample as well as to a combined sample including this GRB sample and an SN Ia sample. Our analysis shows that： a） in the case of assuming an intrinsic distribution of candles of the GRB sample, the effect of the distribution is obvious and should not be neglected; b） taking into account this effect would lead to a poorer constraint of the cosmological parameter ranges. The analysis suggests that in the attempt of constraining the cosmological model with current GRB samples, the results tend to be worse than was previously anticipated if the mentioned intrinsic distribution does exist.

On Dark Gravitational Wave Standard Sirens as Cosmological Inference and Forecasting the Constraint on Hubble Constant using Binary Black Holes Detected by Deci-hertz Observatory

Gravitational wave(GW) signals from compact binary coalescences can be used as standard sirens to constrain cosmological parameters if their redshift can be measured independently by electromagnetic signals.However,mergers of stellar binary black holes(BBHs) may not have electromagnetic counterparts and thus have no direct redshift measurements.These dark sirens may be still used to statistically constrain cosmological parameters by combining their GW measured luminosity distances and localization with deep redshift surveys of galaxies around it.We investigate this dark siren method to constrain cosmological parameters in detail by using mock BBH and galaxy samples.We find that the Hubble constant can be constrained well with an accuracy■ 1% with a few tens or more of BBH mergers at redshift up to 1 if GW observations can provide accurate estimates of their luminosity distance(with relative error of■ 0.01) and localization(■ 0.1 deg^(2)),though the constraint may be significantly biased if the luminosity distance and localization errors are larger.We also introduce a simple method to correct this bias and find it is valid when the luminosity distance and localization errors are modestly large.We further generate mock BBH samples,according to current constraints on BBH merger rate and the distributions of BBH properties,and find that the Deci-hertz Observatory(DO) in a half year observation period may detect about one hundred BBHs with signal-to-noise ratio■■30,relative luminosity distance error■ 0.02 and localization error ■0.01 deg^(2).By applying the dark standard siren method,we find that the Hubble constant can be constrained to the~0.1%-1% level using these DO BBHs,an accuracy comparable to the constraints obtained by using electromagnetic observations in the near future,thus it may provide insight into the Hubble tension.We also demonstrate that the constraint on the Hubble constant applying this dark siren method is robust and does not depend on the choice of the prior for the properties of BBH host galaxies.

Latest cosmological constraints on Cardassian expansion models including the updated gamma-ray bursts

We constrain the Cardassian expansion models from the latest observa- tions, including the updated Gamma-ray bursts （GRBs）, which are calibrated using a cosmology independent method from the Union2 compilation of type Ia supernovae （SNe Ia）. By combining the GRB data with the joint observations from the Union2 SNe Ia set, along with the results from the Cosmic Microwave Background radia- tion observation from the seven-year Wilkinson Microwave Anisotropy Probe and the baryonic acoustic oscillation observation galaxy sample from the spectroscopic Sloan Digital Sky Survey Data Release. we find significant constraints on the model oarameters of the original Cardassian model ΩM0=0.282-0.014^0.015,n=0.03-0.05^＋0.05 and n=-0.16-3.26^＋0.25,β=0.76-0.58^＋0.34 of the modified polytropic Cardassian model, which are consistent with the ACDM model in a l-or confidence region. From the reconstruction of the deceleration parameter q（z） in Cardassian models, we obtain the transition redshift ZT = 0.73 ± 0.04 for the original Cardassian model and ZT = 0.68 ± 0.04 for the modified polytropic Cardassian model.

Inhomogeneous cosmological models in the presence of massless scalar fields

Non-static inhomogeneous cosmological models are obtained in general relativity for the case of a plane symmetric massless scalar field with cosmological constant A, when the source of the gravitational field is a viscous fluid. Some physical and geometrical behaviors of the solutions are also discussed.

Bianchi-V string cosmological model and late time acceleration

We have searched for the existence of the late time acceleration of the universe with string fluid as the source of matter in Bianchi-V space-time. To derive a deterministic solution, we choose the scale factor to be an increasing function of time that yields a time dependent deceleration parameter, representing a model which generates a universe showing a transition from an early decelerating phase to a recent accelerating phase. The study reveals that strings dominate the early universe and eventually disappear from the universe for sufficiently large times, i.e. in the present epoch. This picture is consistent with current astronomical observations. The physical behavior of the universe is discussed in detail.

Cosmological constraints on the DGP braneworld model with gamma-ray bursts

We investigate observational constraints on the Dvali, Gabadadze and Porrati （DGP） model with Gamma-ray bursts （GRBs） at high redshift obtained directly from the Union2 Type Ia supernovae data set. With cosmology-independent GRBs, the Union2 set, as well as the cosmic microwave background observation from the WMAP7 result, the baryon acoustic oscillation, the baryon mass fraction in clus- ters and the observed H（z） data, we obtain that the best-fit values of the DGP model are {ΩM0,Ωrc} = {0.235^＋0.015-0.14, 0.138^＋0.o51-0.048}, which favor a flat universe, and the transition redshift of the DGP model is ZT=0.67^＋0.03-0.04.These results lead to more stringent constraints than the previous results for the DGP model.