Deceleration Parameter Q0 Research Articles

Theoretical Analysis of Moving Galaxies in the Large Scale Structure of SpaceTime

In this paper we will make further theoretical analysis for the validity of the accelerating universe based on General Relativity and three new problems of the standard model of the universe are presented from different perspectives. The first part, analyzed the explosion mechanism of the cosmic initial singularity and put forward a different view from the rest. It’s virtually impossible to start with a giant explosion, the big bang by now cosmologists had refined the idea. The second part devised a new model of the twin paradox. It’s one in which people have been consider to include both special and general relativity in the calculations to expose the counterintuitive weirdness of relativity theory. It seems to has a curious coincidence with the cat-a feline in a locked box that is both dead and alive until the box is opened-was a thought experiment devised by physicist Schr ö dinger. In part three the author makes determination on the cosmological deceleration parameter q0 by using mathematical derivation, and based on which to construct a thought experiment on cosmological redshift. It is needed to make a static model of the universe that both conforms to the Copernican principle and satisfies Hubble’s law and it’s possible to make us a fresh perspective and thought process.

Probing the universe's expansion dynamics: The linear correction scenario perspective on dark energy

In this study, we investigate the cosmological evolution of the universe, focusing on the KMMS models in a model-independent approach, particularly the scenario involving linear correction, given by E2(z)=A(z)+β(1+γB(z)), where A(z)=Ωm0(1+z)3 and B(z)=z. By analyzing recent Cosmic Chronometers (CC) and the Pantheon+ samples, we determine the best-fit values of model parameters using a Markov chain Monte Carlo analysis. Our models exhibit unique dynamics, transitioning from super-exponential to exponential expansion, with a significant shift at redshift zt=0.83−0.10+0.11 and present deceleration parameter q0=−0.69−0.17+0.17. The jerk parameter exceeds 1, indicating a faster change in acceleration than predicted by ΛCDM. The energy density parameter is consistent with Planck observations, and the dark sector evolution follows the expected thermal history. The EoS parameter approaches ωde=−1 over time, with a current value of ωde0=−1.06±0.12, aligning with the phantom phase. Our model presents a new dark energy alternative, emphasizing the importance of considering models like KMMS in understanding cosmic evolution.

The Fast and Furious in JWST high-[formula omitted] galaxies

Recent JWST surveys reveal a striking abundance of massive galaxies at cosmic dawn, earlier than predicted by ΛCDM. The implied speed-up in galaxy formation by gravitational collapse is reminiscent of short-period galaxy dynamics described by the baryonic Tully–Fisher relation. This may originate in weak gravitation tracking the de Sitter scale of acceleration adS=cH, where c is the velocity of light and H(z)∝1+z3/2 is the Hubble parameter with redshift z. With no free parameters, this produces a speed-up in early galaxy formation by an order of magnitude with essentially no change in initial galaxy mass function. It predicts a deceleration parameter q0=1−2π/GAadS2=−0.98±0.5, where G is Newton’s constant and A=(47±6)M⊙(km/s)−4 is the baryonic Tully–Fisher coefficient (McGaugh 2012). At 3σ significance, it identifies dynamical dark energy alleviating H0-tension when combined with independent q0 estimates in the Local Distance Ladder. Conclusive determination of q0=dlog(θ(z)H(z))/dz|z=0 is expected from BAO angle θ(z) observations by the recently launched Euclid mission.

Cosmic evolution in [formula omitted] gravity: Exploring a higher-order time-dependent function of deceleration parameter with observational constraints

In this research paper, we explore a well-motivated parametrization of the time-dependent deceleration parameter, characterized by a cubic form in cosmic time t, in the context of late-time cosmic acceleration. The whole analysis of our work is within the framework of f(Q,T) gravity theory, where we consider the background metric as the homogeneous and isotropic one represented by the Friedmann–Lemaître–Robertson–Walker (FLRW) metric. We solve the field equations with the considered functional form of d(t). In order to find some best fit values of the model parameters and validate our obtained model, we constrain the model using some recent observational datasets, including cosmic chronometer (CC), Supernovae (SNIa), Baryon Acoustic Oscillation (BAO), Cosmic Microwave Background Radiation (CMB), Gamma-ray Burst (GRB), and Quasar (Q) datasets. The joint analysis of these datasets results in tighter constraints for the model parameters, enabling us to discuss both the physical and geometrical aspects of the model. Moreover, we determine the present values of the deceleration parameter (q0), the Hubble parameter (H0), and the transition redshift (zt) from deceleration to acceleration ensuring consistency with some recent results of Planck 2018. Our statistical analysis yields highly improved results, surpassing those obtained in previous investigations. Overall, this study presents valuable insights into the higher order q(t) model and its implications for late-time cosmic acceleration, shedding light on the nature of the late universe.

Model‐Independent Study for a Quintessence Model of Dark Energy: Analysis and Observational Constraints

AbstractIn this paper, a well‐motivated parameterization of the Hubble parameter (H) is revisited that renders two models of dark energy showing some intriguing features of the late‐time accelerating Universe. A general quintessence field is considered as a source of dark energy. Tighter constraints using recently updated cosmic observational datasets for the considered models have been obtained. The two models described here show a nice fit to the considered uncorrelated Hubble datasets, Standard candles, Gamma Ray Bursts, Quasars, and uncorrelated Baryonic Acoustic Oscillations datasets. Using the constrained values of the model parameters, some features of the late‐time accelerating models and obtained the present value of the deceleration parameter (q0), the present value of the Hubble parameter (H0) and the transition redshift () from deceleration to acceleration have been discussed. The current value of the deceleration parameter for both models is consistent with the Planck 2018 results. The evolution of the geometrical and physical parameters is discussed through graphical representations for both models with some diagnostic analysis. The statistical analysis performed here shows greater results and overall, the outcomes of this investigation are superior to those previously found.

Fab-Four Cosmography to Tackle the Hubble Tension

In the context of the Fab-Four theory of gravity in a Friedmann-Lemaître-Robertson-Walker background, in this work we use the cosmography approach to study a particular self-tuning filter solution focused on a zero-curvature fixed point to study the H0 tension. In this scheme, the equations restrict the universe’s evolution to certain scenarios, including radiation-like expansion, matter-like expansion, and late-time acceleration. Furthermore, we build the cosmographic series of the Fab-Four theory to obtain the kinematic parameters as the Hubble constant H0 and the deceleration parameter q0 for all the scenarios mentioned. Finally, we compare our results to find that it is possible to alleviate the current discrepancy on H0 by considering specific requirements on the free parameters of the Fab-Four theory through a self-tuning filter.

Cosmic coincidence problem in interacting holographic dark energy models

It is well known fact that almost the cosmological models for dark energy are suppressed by the coincidence problem. It is worth while studying holographic dark energy model which requires considering the interaction between dark energy and dark matter. In this paper we propose a method for determining parameters of the models so as for the transition redshift zt and the present deceleration parameter q0 to agree with the previous study by means of numerical simulation. By considering the variation of coincidence parameter with the redshift based on the proposed models, we demonstrate that α-model is the most appropriate to explain coincidence problem. Also, this work shows that the direction of flow must be from dark energy to dark matter.

Parametrization of Deceleration Parameter in f(Q) Gravity

In this paper, we investigate the modified symmetric teleparallel gravity or f(Q) gravity, where Q is the nonmetricity, to study the evolutionary history of the universe by considering the functional form of f(Q)=αQn, where α and n are constants. Here, we consider the parametrization form of the deceleration parameter as q=q0+q1z/(1+z)2 (with the parameters q0(q at z=0), q1, and the redshift, z), which provides the desired property for a sign flip from a decelerating to an accelerating phase. We obtain the solution of the Hubble parameter by examining the mentioned parametric form of q, and then we impose the solution in Friedmann equations. Employing the Bayesian analysis for the Observational Hubble data (OHD), we estimated the constraints on the associated free parameters (H0,q0,q1) with H0 the current Hubble parameter to determine if this model may challenge the ΛCDM (Λ cold dark matter with the cosmological constant, Λ) limitations. Furthermore, the constrained current value of the deceleration parameter q0=−0.832−0.091+0.091 shows that the present universe is accelerating. We also investigate the evolutionary trajectory of the energy density, pressure, and EoS (equation-of-state) parameters to conclude the accelerating behavior of the universe. Finally, we try to demonstrate that the considered parametric form of the deceleration parameter is compatible with f(Q) gravity.

Some Studies on K-essence Lagrangian

K-essence Lagrangian is studied in the context of an early universe epoch when t → 0. Equation of state parameter ω < −1 as well as deceleration parameter q0 < −1, indicates an accelerated expansion of the universe at an early epoch of time driven by negative pressure generated by dark energy.

Cosmological Model Insensitivity of Local H0 from the Cepheid Distance Ladder

Abstract The observed tension (∼9% difference) between the local distance ladder measurement of the Hubble constant, H 0, and its value inferred from the cosmic microwave background could hint at new, exotic, cosmological physics. We test the impact of the assumption about the expansion history of the universe ( ) on the local distance ladder estimate of H 0. In the fiducial analysis, the Hubble flow Type Ia supernova (SN Ia) sample is truncated to z < 0.15, and the deceleration parameter (q 0) is fixed to −0.55. We create realistic simulations of the calibrator and Pantheon samples, and account for a full systematics covariance between these two sets. We fit several physically motivated dark-energy models, and derive combined constraints from calibrator and Pantheon SNe Ia and simultaneously infer H 0 and dark-energy properties. We find that the assumption on the dark-energy model does not significantly change the local distance ladder value of H 0, with a maximum difference (ΔH 0) between the inferred value for different models of 0.47 km , i.e., a 0.6% shift in H 0, significantly smaller than the observed tension. Additional freedom in the dark-energy models does not increase the error in the inferred value of H 0. Including systematics covariance between the calibrators, low-redshift SNe, and high-redshift SNe can induce small shifts in the inferred value for H 0. The SN Ia systematics in this study contribute ≲0.8% to the total uncertainty of H 0.

Covariant Canonical Gauge Gravitation and Cosmology

The covariant canonical transformation theory applied to the relativistic Hamiltonian theory of classical matter fields in dynamical space-time yields a novel (first order) gauge field theory of gravitation. The emerging field equations necessarily embrace a quadratic Riemann term added to Einstein’s linear equation. The quadratic term endows space-time with inertia generating a dynamic response of the space-time geometry to deformations relative to (Anti) de Sitter geometry. A “deformation parameter” is identified, the inverse dimensionless coupling constant governing the relative strength of the quadratic invariant in the Hamiltonian, and directly observable via the deceleration parameter q0. The quadratic invariant makes the system inconsistent with Einstein’s constant cosmological term, Λ = const. In the Friedman model this inconsistency is resolved with the scaling ansatz of a “cosmological function”, Λ(a), where a is the scale parameter of the FLRW metric. The cosmological function can be normalized such that with the A CDM parameter set the present-day observables, the Hubble constant and the deceleration parameter, can be reproduced. With this parameter set we recover the dark energy scenario in the late epoch. The proof that inflation in the early phase is caused by the “geometrical fluid” representing the inertia of space-time is yet pending, though. Nevertheless, as according to the CCGG theory the present-day cosmological function, identified with the currently observed Λobs, is a balanced mix of two contributions. These are the (A)dS curvature plus the residual vacuum energy of space-time and matter. The curvature term is proportional to the deformation parameter given by the coupling strength of the quadratic Riemann term. This allows for a fresh look at the Cosmological Constant Problem that plagues the standard Einstein-Friedman cosmology.

Probing Cosmic Acceleration Using Model-independent Parameterizations and Three Kinds of Supernova Statistics Techniques

Abstract In this work, we explore the evolution of the dark energy equation of state ω using Chevalliear–Polarski–Linder parameterization and binned parameterizations. For binned parameterizations, we adopt three methods to choose the redshift interval: (1) ensure that “△z = const,” where △z is the width of each bin; (2) ensure that “n△z = const,” where n is the number of SN Ia in each bin; and (3) treat redshift discontinuity points as model parameters, i.e., “free △z.” For observational data, we adopt JLA SN Ia samples, SDSS DR12 data, and Planck 2015 distance priors. In particular, for JLA SN Ia samples, we consider three statistic techniques: magnitude statistics, which is the traditional method; flux statistics, which reduces the systematic uncertainties of SN Ia; and improved flux statistics, which can reduce the systematic uncertainties and give tighter constrains at the same time. The results are as follows. For all the cases, ω = −1 is always satisfied at the 1σ confidence regions; this means that ΛCDM is still favored by current observations. For magnitude statistics, the “free △z” model will give the smallest error bars. However, this conclusion does not hold true for flux statistics and improved flux statistic. The improved flux statistic yields the largest present fractional density of matter Ω m ; in addition, this technique will give the largest current deceleration parameter q 0 , which reveals the universe with the slowest cosmic acceleration.

SNe Ia Redshift in a Nonadiabatic Universe

By relaxing the constraint of adiabatic universe used in most cosmological models, we have shown that the new approach provides a better fit to the supernovae Ia redshift data with a single parameter, the Hubble constant H0, than the standard ΛCDM model with two parameters, H0 and the cosmological constant Λ related density, ΩΛ. The new approach is compliant with the cosmological principle. It yields the H0 = 68.28 (±0.53) km s−1 Mpc−1 with an analytical value of the deceleration parameter q0 = −0.4. The analysis presented is for a matter-only, flat universe. The cosmological constant Λ may thus be considered as a manifestation of a nonadiabatic universe that is treated as an adiabatic universe.

An improved model-independent assessment of the late-time cosmic expansion

In the current work, we have implemented an extension of the standard Gaussian Process formalism, namely the Multi-Task Gaussian Process with the ability to perform a joint learning of several cosmological data simultaneously. We have utilised the “low-redshift” expansion rate data from Supernovae Type-Ia (SN), Baryon Acoustic Oscillations (BAO) and Cosmic Chronometers (CC) data in a joint analysis. We have tested several possible models of covariance functions and find very consistent estimates for cosmologically relevant parameters. In the current formalism, we also find provisions for heuristic arguments which allow us to select the best-suited kernel for the reconstruction of expansion rate data. We also utilised our method to account for systematics in CC data and find an estimate of H0 = 68.52+0.94 + 2.51 (sys)−0.94 km/s Mpc−1 and a corresponding rd = 145.61+2.82 − 2.82 − 4.3 (sys) Mpc as our primary result. Subsequently, we find constraints on the present deceleration parameter q0 = −0.52 ± 0.06 and the transition redshift zT = 0.64+0.12−0.09. All the estimated cosmological parameters are found to be in good agreement with the standard ΛCDM scenario. Including the local model-independent H0 estimate to the analysis we find H0 = 71.40 + 0.30 + 1.65 (sys)− 0.30 km/s Mpc−1 and the corresponding rd = 141.29 + 1.31 −1.31−2.63 (sys) Mpc. Also, the constraints on rd H0 remain consistent throughout our analysis and also with the model-dependent CMB estimate. Using the \U0001d4aam(z) diagnostic, we find that the concordance model is very consistent within the redshift range z ≲ 2 and mildly discrepant for z ≳ 2.

Static and Dynamic Components of the Redshift

We analyse the possibility that the observed cosmological redshift may be cumulatively due to the expansion of the universe and the tired light phenomenon. Since the source of both the redshifts is the same, they both independently relate to the same proper distance of the light source. Using this approach we have developed a hybrid model combining the Einstein de Sitter model and the tired light model that yields a slightly better fit to Supernovae Ia redshift data using one parameter than the standard ΛCDM model with two parameters. We have shown that the ratio of tired light component to the Einstein de Sitter component of redshift has evolved from 2.5 in the past, corresponding to redshift 1000, to its present value of 1.5. The hybrid model yields Hubble constant H0 =69.11(±0.53)km·s-1 ·Mpc-1 and the deceleration parameter q0 =-0.4. The component of Hubble constant responsible for expansion of the universe is 40% of H0 and for the tired light is 60% of H0. Consequently, the critical density is only 16% of its currently accepted value; a lot less dark matter is needed to make up the critical density. In addition, the best data fit yields the cosmological constant density parameter =0. The tired light effect may thus be considered equivalent to the cosmological constant in the hybrid model.

Constraining the cosmic deceleration-acceleration transition with type Ia supernova, BAO/CMB and H(z) data

We revisit the kink-like parametrization of the deceleration parameter q(z) [1], which considers a transition, at redshift zt, from cosmic deceleration to acceleration. In this parametrization the initial, at z ≫ zt, value of the q-parameter is qi, its final, z=−1, value is qf and the duration of the transition is parametrized by τ. By assuming a flat space geometry we obtain constraints on the free parameters of the model using recent data from type Ia supernovae (SN Ia), baryon acoustic oscillations (BAO), cosmic microwave background (CMB) and the Hubble parameter H(z). The use of H(z) data introduces an explicit dependence of the combined likelihood on the present value of the Hubble parameter H0, allowing us to explore the influence of different priors when marginalizing over this parameter. We also study the importance of the CMB information in the results by considering data from WMAP7, WMAP9 (Wilkinson Microwave Anisotropy Probe—7 and 9 years) and Planck 2015. We show that the contours and best fit do not depend much on the different CMB data used and that the considered new BAO data is responsible for most of the improvement in the results. Assuming a flat space geometry, qi=1/2 and expressing the present value of the deceleration parameter q0 as a function of the other three free parameters, we obtain zt=0.67+0.10−0.08, τ=0.26+0.14−0.10 and q0=−0.48+0.11−0.13, at 68% of confidence level, with an uniform prior over H0. If in addition we fix qf=−1, as in flat ΛCDM, DGP and Chaplygin quartessence that are special models described by our parametrization, we get zt=0.66+0.03−0.04, τ=0.33+0.04−0.04 and q0=−0.54+0.05−0.07, in excellent agreement with flat ΛCDM for which τ=1/3. We also obtain for flat wCDM, another dark energy model described by our parametrization, the constraint on the equation of state parameter −1.22 < w < −0.78 at more than 99% confidence level.

Modified Chaplygin gas cosmology with observational constraints

The spatially homogeneous and totally anisotropic Bianchi type-II space-time models with modified Chaplygin gas having the equation of state p=Aρ−Bρα, 0 ≤ A ≤ 1, 0 ≤ α ≤ 1, where A, α and B are positive constants, have been investigated. It has been shown that the equation of state for such modified model is valid from the radiation era to the ΛCDM. The statefinder, which is the cosmological diagnostic pair {r, s} has been adopted to characterize different phases of the universe. The physical and geometrical properties of the corresponding cosmological models have been discussed. The observational constraints, essentially dependent on the hubble parameter H0 and deceleration parameter q0 have been investigated using 28 data points of H(z), SNe Ia and H(z)+ SNe Ia [57]. It has been seen that the average scale factor a(t) can be expanded in terms of an infinite convergent series around the current value of the average scale factor a0 using Taylor’s theorem, in which the current value of the deceleration parameter q0, the dimensionless jerk parameter j0, the snap parameter s0* and the lerk parameter ℓ0 appeared.

ANISOTROPY OF COSMIC ACCELERATION

In this paper, we study the anisotropy of cosmic acceleration by dividing the Union2 Type Ia supernova (SNIa) dataset into 12 subsets according to their positions in Galactic coordinate system. In each region, we derive the deceleration parameter q0 as the diagnostic to quantify the anisotropy level in the corresponding direction, and construct q0 anisotropic maps by combining these q0 values. In addition to the monopole component, we find the significant dipole effect in the q0-maps with the amplitude [Formula: see text], which deviates from zero at more than 2-σ level. The direction of the best-fit dipole is (θ = 108.8°, ϕ = 187.0°) in Galactic system. Interesting enough, we find the direction of this dipole is nearly perpendicular to the CMB kinematic dipole, and the angle between them is 95.7°. The perpendicular relation is anomalous at the 1-in-10 level.

Measuring accelerating universe with high-redshift GRBs data and other cosmological probes

A kinematical model (a parameterized deceleration parameter) and a dynamical model (a parameterized equation of state for dark energy) are constrained from the current observational data including the high-redshift Gamma-Ray Bursts (GRBs) data with a redshift range from 1.4 to 9. We obtain the stringent constraint on the values of current deceleration parameter q 0, current jerk parameter j 0, current equation of state for dark energy w 0de and transition redshift z T. In addition, we compare the difference of the constraint results between the kinematical and the dynamical scenarios.

Direction dependence of the deceleration parameter

In this paper we study the possibly existing anisotropy in the accelerating expansion Universe by use of the full sample of Union2 data. Using the hemisphere comparison method to search for a preferred direction, we take the deceleration parameter q0 as the diagnostic to quantify the anisotropy level in the wCDM model. We find that the maximum accelerating expansion direction is (l,b) = (314°+20°−13°,28°+11°−33°), with the maximum anisotropy level of Δq0,max/q̄0 = 0.79+0.27−0.28, and that the anisotropy is more prominent when only low redshift data (z ⩽ 0.2) are used. We also discuss this issue in the CPL parameterized model, showing a similar result.