Hubble Parameter Research Articles

Simultaneous measurements on cosmic curvature and opacity using latest HII regions and H(z) observations

The different spatial curvatures of the universe affect the measurement of cosmological distances, which may also contribute to explaining the observed dimming of type Ia supernovae. This phenomenon may be caused by the opacity of the universe. Similarly, the opacity of the universe can lead to a bias in our measurements of curvature. Thus, it is necessary to measure cosmic curvature and opacity simultaneously. In this paper, we propose a new model-independent method to simultaneously measure the cosmic curvature and opacity by using the latest observations of HII galaxies acting as standard candles and the latest Hubble parameter observations. The machine learning method-Artificial Neural Network is adopted to reconstruct observed Hubble parameter H(z) observations. Our results support a slightly opaque and flat universe at 1sigma confidence level by using previous 156 HII regions sample. However, the negative curvature is obtained by using the latest 181 HII regions sample in the redshift range zsim 2.5. More importantly, we obtain the simultaneous measurements with precision on the cosmic opacity mathrm Delta tau sim 10^{-2} and curvature mathrm Delta Omega _Ksim 10^{-1}. A strong degeneracy between the cosmic opacity and curvature parameters is also revealed in this analysis.

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.

How to Predict the Temperature of the CMB Directly Using the Hubble Parameter and the Planck Scale Using the Stefan-Boltzmann Law

How to Predict the Temperature of the CMB Directly Using the Hubble Parameter and the Planck Scale Using the Stefan-Boltzmann Law

Evidence of dynamical dark energy in a non-flat universe: current and future observations

We investigate the dark energy phenomenology in an extended parameter space where we allow the curvature density of our universe as a free-to-vary parameter. The inclusion of the curvature density parameter is motivated from the recently released observational evidences indicating the closed universe model at many standard deviations. Here we assume that the dark energy equation-of-state follows the PADE approximation, a generalized parametrization that may recover a variety of existing dark energy models. Considering three distinct PADE parametrizations, labeled as PADE-I, SPADE-I and PADE-II, we first constrain the cosmological scenarios driven by them using the joint analyses of a series of recently available cosmological probes, namely, Pantheon sample of Supernovae Type Ia, baryon acoustic oscillations, big bang nucleosynthesis, Hubble parameter measurements from cosmic chronometers, cosmic microwave background distance priors from Planck 2018 and then we include the future Gravitational Waves standard sirens (GWSS) data from the Einstein telescope with the combined analyses of these current cosmological probes. We find that the current cosmological probes indicate a very strong evidence of a dynamical dark energy at more than 99% C.L. in both PADE-I, and PADE-II, but no significant evidence for the non-flat universe is found in any of these parametrizations. Interestingly, when the future GWSS data from the Einstein telescope are included with the standard cosmological probes an evidence of a non-flat universe is found in all three parametrizations together with a very strong preference of a dynamical dark energy at more than 99% C.L. in both PADE-I, and PADE-II. Although from the information criteria analysis, namely, AIC, BIC, DIC, the non-flat Λ-Cold Dark Matter model remains the best choice, however, in the light of DIC, PADE parametrizations are still appealing.

MATHEMATICAL ANALYSIS OF COSMOLOGICAL MODELS WITH LINEARLY VARYING DECELERATION PARAMETER

Bianchi type-V is investigated using a decaying cosmological constant with perfect fluid. The study solves Einstein field equations by assuming that the deceleration parameter q is functionally connected to the Hubble parameter H, which yields the scale factor a. As cosmic time t increases, the cosmological model experiences exponential inflation. The physical characteristics and behavior of the cosmological model are also covered.

A model for time-evolution of coupling constants

A general model is proposed for time-varying coupling constants in field theory, assuming the ultraviolet cutoff is a varying entity in the expanding universe. It is assumed that the cutoff depends on the scale factor of the universe and all bare couplings remain constant. This leads to varying renormalized coupling constants that evolve in proportion to the Hubble parameter. The evolution of the standard model constants is discussed.

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.

Reconstructing the Hubble Parameter with Future Gravitational-wave Missions Using Machine Learning

We study the prospects of Gaussian processes (GPs), a machine-learning (ML) algorithm, as a tool to reconstruct the Hubble parameter H(z) with two upcoming gravitational-wave (GW) missions, namely, the evolved Laser Interferometer Space Antenna (eLISA) and the Einstein Telescope (ET). Assuming various background cosmological models, the Hubble parameter has been reconstructed in a nonparametric manner with the help of a GP using realistically generated catalogs for each mission. The effects of early-time and late-time priors on the reconstruction of H(z), and hence on the Hubble constant (H 0), have also been focused on separately. Our analysis reveals that a GP is quite robust in reconstructing the expansion history of the Universe within the observational window of the specific missions under consideration. We further confirm that both eLISA and ET would be able to provide constraints on H(z) and H 0, which would be competitive to those inferred from current data sets. In particular, we observe that an eLISA run of a ∼10 yr duration with ∼80 detected bright siren events would be able to constrain H 0 as precisely as a ∼3 yr ET run assuming ∼1000 bright siren event detections. Further improvement in precision is expected for longer eLISA mission durations such as a ∼15 yr time frame having ∼120 events. Lastly, we discuss the possible role of these future GW missions in addressing the Hubble tension, for each model, on a case-by-case basis.

Post-reionization H i 21-cm signal: a probe of negative cosmological constant

ABSTRACT In this study, we investigate a cosmological model involving a negative cosmological constant (AdS vacua in the dark energy sector). We consider a quintessence field on top of a negative cosmological constant and study its impact on cosmological evolution and structure formation. We use the power spectrum of the redshifted H i 21-cm brightness temperature maps from the post-reionization epoch as a cosmological probe. The signature of baryon acoustic oscillations (BAO) on the multipoles of the power spectrum is used to extract measurements of the angular diameter distance DA(z) and the Hubble parameter H(z). The projected errors on these are then subsequently employed to forecast the constraints on the model parameters ($H_0, \Omega _{m}, \Omega _\Lambda , w_0, w_a$) using Markov chain Monte Carlo techniques. We find that a negative cosmological constant with a phantom dark energy equation of state (EoS) and a higher value of H0 is viable from BAO distance measurements data derived from galaxy samples. We also find that BAO imprints on the 21-cm power spectrum obtained from a futuristic SKA-mid like experiment yield a 1σ error on a negative cosmological constant and the quintessence dark energy EoS parameters to be $\Omega _\Lambda =-1.030^{0.589}_{-1.712}$ and $w_0=-1.023^{0.043}_{-0.060}$, $w_a=-0.141^{0.478}_{-0.409}$ respectively.

Matter bounce scenario in matter geometry coupled theory

This paper studies the cosmographic and matter bounce scenario in modified theory. The corresponding field equations are evaluated after considering special corrections of a Hubble parameter. The linear corrections to the Gauss-Bonnet gravity are being taken to analyze the behavior of Hubble and deceleration parameters. We derive dynamical parameters in a very general way to analyze different energy conditions that would lead to understanding the behavior of the equation of state parameters in cosmography. Finally, the removal of the initial singularity is observed to understand the late-time cosmic acceleration.

Measuring cosmic bulk flow with Pantheon catalogue in perturbed f(R) gravity

ABSTRACT This study investigates the cosmic bulk flow through an analysis of luminosity distance variations in a perturbed Friedmann universe governed by f(R) gravity. The Hubble parameter, derived from perturbed Friedmann equations capturing intrinsic temporal fluctuations, is crucial. Redshift tomography is used to analyse observational data from the Pantheon catalogue from 0.015 to z < 2.3. Our objective is to constrain the cosmic bulk flow’s direction and magnitude within this redshift range. At low redshifts (z < 0.06), the predominant bulk flow aligns with the dominating supercluster in the corresponding range, maintaining a relatively constant magnitude, consistent with Lambda cold dark matter (ΛCDM) model predictions. A shift towards (l, b) = (290 ± 21, 15 ± 20) with $v_{\mathrm{bulk}} = 774 \pm 83 \, \mathrm{km\, s}^{-1}$ occurs between 0.06 < z < 0.1, coinciding with the cosmic microwave background dipole. For 0.1 < z < 0.2, the bulk flow shifts to (l, b) = (270 ± 21, 25 ± 20) with $v_{\mathrm{bulk}} = 903 \pm 102 \, \mathrm{km\, s}^{-1}$, supporting Kashlinsky et al.’s result. Beyond z > 0.2, the bulk flow’s magnitude exceeds $1000 \, \mathrm{km\, s}^{-1}$, deviating from ΛCDM model expectations. Our findings suggest that matter density oscillations under f(R) gravity exhibit ΛCDM model properties at low redshifts. However, the microwave background anisotropy shows noticeable fluctuations at higher redshifts, validating prior findings of strong cosmic bulk flows at these scales.

Analyzing quantum gravity spillover in the semiclassical regime

One of the standard approaches of incorporating the quantum gravity (QG) effects into the semiclassical analysis is to adopt the notion of a quantum-corrected spacetime arising from the QG model. This procedure assumes that the expectation value of the metric variable effectively captures the relevant QG subtleties in the semiclassical regime. We investigate the viability of this effective geometry approach for the case of dust dominated and a dark energy dominated universe. We write the phase space expressions for the geometric observables and construct corresponding Hermitian operators. A general class of operator ordering of these observables is considered, and their expectation values are calculated for a unitarily evolving wave packet. In the case of dust dominated universe, the expectation value of the Hubble parameter matches the “semiclassical” expression, the expression computed from the scale factor expectation value. In the case of the Ricci scalar, the relative difference between the semiclassical expression and quantum expectation is maximum at singularity and decays for late time. For a cosmological constant driven universe, the difference between the semiclassical expressions and the expectation value is most pronounced far away from the bounce point, hinting at the persistent quantum effect at the late time. The parameter related to the shape of the distribution appears as a control parameter in these models. In the limit of a sharply peaked distribution, the expectation value of the observables matches with their semiclassical counterpart, and the usage of effective geometry approach is justified.

Viscous effect in the late time evolution of phantom universe

We investigate the cosmological implications of a phantom dark energy model with bulk viscosity. We explore this model as a possible way to resolve the big rip singularity problem that plagues the phantom models. We use the latest type Ia supernova and Hubble parameter data to constrain the model parameters and find that the data favor a significant bulk viscosity over a non-constant potential term for the phantom field. We perform a dynamical analysis of the model and show that the only stable and physical attractor corresponds to a phantom-dominated era with a total equation of state that can be greater than -1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-1$$\\end{document} due to the viscosity. We also study the general effect of viscosity on the phantom field and the late time evolution of the universe. We apply the statefinder diagnostic to the model and find that it approaches a nearby fixed point asymptotically, indicating that the universe can escape the big rip singularity with the presence of bulk viscosity. We conclude that bulk viscosity can play an important role in affecting the late-time behavior as well as alleviating the singularity problem of the phantom universe.

Stringy running vacuum model and current tensions in cosmology

We discuss the potential alleviation of both the Hubble and the growth of galactic structure data tensions observed in the current epoch of cosmology in the context of the so-called stringy running vacuum model (RVM) of cosmology. This is a gravitational field theory coupled to matter, which, at early eras, contains gravitational (Chern–Simons (CS) type) anomalies and torsion, arising from the fundamental degrees of freedom of the massless gravitational multiplet of an underlying microscopic string theory. The model leads to RVM type inflation without external inflatons, arising from the quartic powers of the Hubble parameter that characterize the vacuum energy density due to primordial-gravitational-wave-induced anomaly CS condensates, and dominate the inflationary era. In modern eras, of relevance to this work, the gravitational anomalies are cancelled by chiral matter, generated at the end of the RVM inflationary era, but cosmic radiation and other matter fields are still responsible for a RVM energy density with terms exhibiting a quadratic-power-of-Hubble-parameter dependence, but also products of the latter with logarithmic H-dependencies, arising from potential quantum-gravity and quantum-matter loop effects. In this work, such terms are examined phenomenologically from the point of view of the potential alleviation of the aforementioned current tensions in cosmology. Using standard information criteria, we find that these tensions can be substantially alleviated in a way consistent not only with the data, but also with the underlying microscopic theory predictions, associated with the primordial dynamical breaking of supergravity that characterize a pre-RVM-inflationary phase of the model.

Investigating the dark energy phenomenon in [formula omitted] cosmological models with observational constraints

This paper explores the dark energy phenomenon within the context of f(R,Lm) gravity theory. Two specific non-linear f(R,Lm) models are considered: f(R,Lm)=R2+Lmα and f(R,Lm)=R2+(1+αR)Lm, where the parameter α is free. Here, we adopt a parametrization form for the Hubble parameter in terms of redshift z as H(z)=H0A(1+z)3+B+ϵlog(1+z)12, which allows for deviations from the standard ΛCDM model at both low and high redshifts. We then incorporate the Hubble parameter solution into the Friedmann equations for both models. We employ Bayesian analysis to estimate the constraints on the free parameters H0, A, B, and ϵ using the Hubble measurements and the Pantheon dataset. Further, we investigate the evolution of key cosmological quantities, such as the deceleration parameter, energy density, pressure, EoS parameter, and energy conditions. The evolution of the deceleration parameter reveals a significant transition from a decelerating phase to an accelerating phase in the Universe. The EoS parameter exhibits quintessence-like behavior for both non-linear f(R,Lm) models.

Oscillating quintom scenario with time-dependent periodic deceleration parameter

In this paper, we introduced the deceleration parameter [Formula: see text] in a different manner by proposing a modern law. According to this law, we suggested a time-periodic [Formula: see text]. Furthermore, we used this law to develop a model in which the universe oscillates with quintom matter in a four-dimensional FLRW metric background. Using this model, we obtained the oscillating Hubble parameter [Formula: see text], which remains positive. Consequently, the universe undergoes decelerating expansion and accelerating expansion periodically, avoiding singularities.

Probing accelerating cosmos via reconstructed Hubble parameter and its influence on f(T) gravity models

This article introduces a new way of studying the accelerating cosmos without relying on specific models. It proposes a new parametric form of the Hubble parameter (HP) and uses a Markov Chain Monte Carlo (MCMC) approach to determine the model parameters. The analysis incorporates a comprehensive dataset consisting of 34 cosmic chronometers (CC) data points, 40 non-correlated baryonic acoustic oscillations (BAO) points, and 1701 updated Pantheon+ supernovae type Ia (SNeIa) data points. The study investigates various aspects of the model's behavior, such as the transition from deceleration to acceleration, and the evolution of jerk and snap parameters. Constraints are applied to the model parameters as well as the Hubble constant (H0). Additionally, the parameter values obtained are used to study f(T) gravity models and compare them with observational data. This research provides valuable insights into the nature of the accelerating Universe and highlights the importance of using a parametrized approach in cosmological studies.

Dark Matter Cosmology with Varying Viscosity: A Possible Resolution to the S 8 Tension

We study varying forms of viscous dark matter (DM) and try to address the intriguing tensions of the standard model of cosmology with recent cosmological data, including the Hubble and S 8 tensions. We note that by assuming the DM viscosity depends on the Hubble parameter, DM density, or both, one can improve the statistics. Although the models tend to aggravate the Hubble tension a bit, they tend to reduce the S 8 tension, even in comparison with the constant viscosity case. Since similar-to-viscosity massive neutrinos suppress the power spectrum of matter on small length scales, considering them along with the viscous DM, we find that the neutrino mass range is tightened.

Emergent Unparticles Dark Energy can restore cosmological concordance

Addressing the discrepancy between the late and early time measurements of the Hubble parameter, H 0, and the so-called S 8 parameter has been a challenge in precision cosmology. Several models are present to address these tensions, but very few of them can do so simultaneously. In the past, we have suggested Banks-Zaks/Unparticles as an emergent Dark Energy model, and claimed that it can ameliorate the Hubble tension. In this work, we test this claim, and perform a likelihood analysis of the model and its parameters given current data, and compare it to ΛCDM. The model offers a possible resolution of Hubble tension and softens the Large Scale Structure (LSS) tension without employing a scalar field or modifying the gravitational sector. Our analysis shows a higher value of H 0 ∼ 70 – 73 km/sec/Mpc and a slightly lower value of S 8 for certain combinations of data sets. Consideration of Planck CMB data combined with the Pantheon sample and SH0ES priors lowers the H 0 and S 8 tension to 0.96σ and 0.94σ respectively with best-fit Δχ 2 ≈ -11 restoring cosmological concordance. Significant improvement in the likelihood persists for other combinations of data sets as well. Evidence for the model is given by inferring one of its parameters to be x 0 ≃ -4.46.The improvement in the fit is driven by the inclusion of the SH0ES prior. In its absence most of the improvement is due to larger error bars in the Emergent Unparticles Dark Energy model.

The backreaction effect of sound speed resonance in DBI inflation

We examine the backreaction effect of the enhanced small-scale scalar perturbations from the sound speed resonance (SSR) mechanism for primordial black hole formation in Dirac-Born-Infeld (DBI) inflation Within the perturbative regime, the backreaction effect of perturbations on the background dynamics can be described by an effective action after integrating out the perturbation sector. Starting with the effective field theory of a specific DBI inflation model that incorporates SSR, we obtain the one-loop effective action by integrating out the scalar perturbations at the quadratic level. Using the effective Friedmann equations derived from this one-loop effective action, we solve the Hubble parameter with backreaction and the effective perturbation dynamics on this background as well. Our numerical findings reveal that, for a viable parameter space, the backreaction effect results in a relative correction to the Hubble parameter of approximately 10−7, whereas the relative correction to the slow-roll parameter can vary between −0.3 and 0.1, before gradually converging to 10−7. Furthermore, our results show that the backreaction effect on SSR sound speed causes a slight reduction in the resonant peak of the curvature power spectrum, and the subsequent PBH formation predicted by the SSR mechanism remains almost unchanged.