Hubble Parameter Research Articles

Dynamical analysis of the Tsallis holographic dark energy models with event horizon as cut-off and interaction with matter

The model of generalized Tsallis holographic dark energy (which is known to be particular representative of Nojiri–Odintsov HDE) with event horizon as cut-off is investigated using methods of dynamical analysis. We take into consideration possible interaction with dark energy and matter in various forms. Critical points are determined. Cosmological evolution of the universe depends from interaction parameters. If we use event horizon scale as cut-off quasi-de Sitter expansion is possible only for interaction of type [Formula: see text] (where [Formula: see text] is the Hubble parameter). For interactions [Formula: see text] and [Formula: see text] universe eventually stops ([Formula: see text]) or ends its existence in final singularity ([Formula: see text]). In the first case, fraction of dark energy tends to [Formula: see text] or constant value lesser than 1 because dynamical equilibrium between matter and dark energy is established on late times.

A non-singular bouncing cosmology in f(R,T) gravity

We investigate a bounce realization in the framework of higher order curvature in f(R,T) modified theory of gravity. We perform a detailed analysis of the cosmological parameters to explain the contraction phase, the bounce phase, and the expansion phase. Furthermore, we observe a violation of the null energy condition, instability of the model, and a singularity upon deceleration at the bouncing point, which are the supporting results for a bouncing cosmology. The equation of state parameter exhibits a ghost condensate behavior of the model near the bouncing point. Additionally, we discuss the stability of the model using linear perturbations in the Hubble parameter as well as the energy density.

From inflation to reheating and their dynamical stability analysis in Gauss–Bonnet gravity

We investigate the inflation and reheating phenomenology in scalar-Einstein-Gauss–Bonnet theory of gravity where a scalar field non-minimally couples with the Gauss-Bonnet (GB) curvature term. Regarding the inflationary phenomenology, we find – (1) the inflation starts with a quasi de-Sitter phase and has an exit at a finite e-fold, which is indeed consistent with the resolution of horizon and flatness problems, (2) the scalar and tensor perturbations prove to be ghost free and do not suffer from gradient instability, (3) the curvature perturbation amplitude as well as its tilt and the tensor-to-scalar ratio turn out to be simultaneously compatible with the recent Planck data for suitable values of the parameters which also results to the inflationary energy scale ∼1012GeV. After the inflation ends, the scalar field starts to decay to radiation with a constant decay width. For our considered scalar potential and the GB coupling function, the model results to an analytic power law solution of the Hubble parameter and a logarithmic solution of the scalar field during the reheating era, where the exponent of the Hubble parameter determines the effective EoS parameter (weff) during the same. The stability of such reheating dynamics is examined by dynamical analysis which ensures that weff can go beyond unity and reach up-to the maximum value of max(weff)=1.56. The scenario with weff>1 proves to be purely due to the presence of the GB coupling function, which in turn may have important consequences on enhancing the primordial gravitational waves’ amplitude observed today. The inflationary e-fold number (Nf) gets further constrained by the input of the reheating stage, and we critically examine the constraint of Nf coming from both the inflation and reheating phenomenology. We finally construct the complete forms of scalar potential (V(ϕ)) and the GB coupling function (ξ(ϕ)) that smoothly transits from inflation to reheating, and numerically solve the Hubble parameter and the scalar field for such complete forms of V(ϕ) and ξ(ϕ). Such numerical solutions match with analytic ones in the respective regime. After the reheating ends, the GB term gets decouple from the theory and the radiation energy density dominates the energy budget of the universe, which in turn produces the standard radiation era of the universe.

A constrained cosmological model in [formula omitted] gravity

In this article, we study the expanding nature of the universe in the context of f(R,Lm) gravity theory, here R represents the Ricci scalar and Lm is the matter Lagrangian density. With a specific form of f(R,Lm), we obtain the field equations for flat FLRW metric. We parametrize the deceleration parameter in terms of the Hubble parameter and from here we find four free parameters, which are constraints and estimated by using H(z), Pantheon, and their joint data sets. Further, we investigate the evolution of the deceleration parameter which depicts a transition from the deceleration to acceleration phases of the universe. The evolutionary behaviour of energy density, pressure, and EoS parameter shows that the present model is an accelerated quintessence dark energy model. To compare our model with the ΛCDM model we use some of the diagnostic techniques. Thus, we find that our model in f(R,Lm) gravity supports the recent standard observational studies and delineates the late-time cosmic acceleration.

Constraining the gravitational-wave spectrum from cosmological first-order phase transitions using data from LIGO-Virgo first three observing runs

We search for a first-order phase transition (PT) gravitational wave (GW) signal from Advanced LIGO and Advanced Virgo's first three observing runs. Due to the large theoretical uncertainties, four shapes of GW energy spectral from bubble and sound wave collisions widely adopted in literature are investigated, separately. Our results indicate that there is no evidence for the existence of such GW signals, and therefore we give the upper limits on the amplitude of GW energy spectrum Ωpt(f *) in the peak frequency range of f * ∈ [5,500] Hz for these four theoretical models, separately. We find that Ωpt(f * ≃ 40 Hz) < 1.3 × 10-8 at 95% credible level, and roughly H */β ≲ 0.1 and α ≲ 1 at 68% credible level in the peak frequency range of 20 ≲ f * ≲ 100 Hz corresponding to the mostsensitive frequency band of Advanced LIGO and Advanced Virgo's first three observing runs, where H * is the Hubble parameter when PT happens, β is the bubble nucleation rate and α is the normalized latent heat.

Data-driven and almost model-independent reconstruction of modified gravity

In this paper, a modified factor μ, which characterizes modified gravity in the linear matter density perturbation theory, is reconstructed in a data-driven and almost model-independent way via Gaussian process by using currently available cosmic observations. Utilizing the Pantheon+ SNe Ia samples, the observed Hubble parameter H(z) and the redshift space distortion fσ 8(z) data points, one finds out a time varying μ at low redshifts. The reconstructed μ implies that more complicated modified gravity beyond the simplest general relativity and the Dvali-Gabadadze-Porrati braneworld model is required.

Constraints on the Cosmic Expansion History from GWTC–3

We use 47 gravitational wave sources from the Third LIGO–Virgo–Kamioka Gravitational Wave Detector Gravitational Wave Transient Catalog (GWTC–3) to estimate the Hubble parameter H(z), including its current value, the Hubble constant H 0. Each gravitational wave (GW) signal provides the luminosity distance to the source, and we estimate the corresponding redshift using two methods: the redshifted masses and a galaxy catalog. Using the binary black hole (BBH) redshifted masses, we simultaneously infer the source mass distribution and H(z). The source mass distribution displays a peak around 34 M ⊙, followed by a drop-off. Assuming this mass scale does not evolve with the redshift results in a H(z) measurement, yielding H0=68−8+12kms−1Mpc−1 (68% credible interval) when combined with the H 0 measurement from GW170817 and its electromagnetic counterpart. This represents an improvement of 17% with respect to the H 0 estimate from GWTC–1. The second method associates each GW event with its probable host galaxy in the catalog GLADE+, statistically marginalizing over the redshifts of each event’s potential hosts. Assuming a fixed BBH population, we estimate a value of H0=68−6+8kms−1Mpc−1 with the galaxy catalog method, an improvement of 42% with respect to our GWTC–1 result and 20% with respect to recent H 0 studies using GWTC–2 events. However, we show that this result is strongly impacted by assumptions about the BBH source mass distribution; the only event which is not strongly impacted by such assumptions (and is thus informative about H 0) is the well-localized event GW190814.

Observational constraints on the modification of standard ΛCDM cosmology with dark radiation

We revisit a cosmological model modified by an extra “radiation-like” energy component in the Universe, which can be interpreted as many physical phenomena. Here, we derive the constraint on the energy density from this modification with current cosmological observations, including Cosmic Microwave Background, Baryon Acoustic Oscillation, Observational Hubble Parameter data and Type Ia supernovae. Performing a Bayesian analysis gives at 95% confidence level. Our work shows the dark radiation energy is small. Alleviating H 0 tension by introducing this term can also be interpreted as the systematic error caused by the numerical method.

A thorough investigation of the prospects of eLISA in addressing the Hubble tension: Fisher forecast, MCMC and Machine Learning

We carry out an in-depth analysis of the capability of the upcoming space-based gravitational wave mission eLISA in addressing the Hubble tension, with a primary focus on observations at intermediate redshifts (3 < z < 8). We consider six different parametrizations representing different classes of cosmological models, which we constrain using the latest datasets of cosmic microwave background (CMB), baryon acoustic oscillations (BAO), and type Ia supernovae (SNIa) observations, in order to find out the up-to-date tensions with direct measurement data. Subsequently, these constraints are used as fiducials to construct mock catalogs for eLISA. We then employ Fisher analysis to forecast the future performance of each model in the context of eLISA. We further implement traditional Markov Chain Monte Carlo (MCMC) to estimate the parameters from the simulated catalogs. Finally, we utilize Gaussian Processes (GP), a machine learning algorithm, for reconstructing the Hubble parameter directly from simulated data. Based on our analysis, we present a thorough comparison of the three methods as forecasting tools. Our Fisher analysis confirms that eLISA would constrain the Hubble constant (H 0) at the sub-percent level. MCMC/GP results predict reduced tensions for models/fiducials which are currently harder to reconcile with direct measurements of H 0, whereas no significant change occurs for models/fiducials at lesser tensions with the latter. This feature warrants further investigation in this direction.

Early dark energy with power-law F(R) gravity

We study a power-law F(R) gravity with an early dark energy term, that can describe both the early-time and the late-time acceleration of the Universe. We confront this scenario with recent observational data including the Pantheon Type Ia supernovae, measurements of the Hubble parameter H(z) (Cosmic Chronometers), data from Baryon Acoustic Oscillations and standard rulers data from the Cosmic Microwave Background (CMB) radiation. The model demonstrates some achievements in confronting with these observations and can be compared with the Λ-Cold-Dark-Matter model. In particular, in both models we obtain very close estimates for the Hubble constant H0, but it is not true for Ωm0. The early dark energy term supports viability of the considered F(R) gravity model.

Evidence of a decreasing trend for the Hubble constant

The current discrepancy between the Hubble constant, H0, derived from the local distance ladder and from the cosmic microwave background is one of the most crucial issues in cosmology, as it may possibly indicate unknown systematics or new physics. Here, we present a novel non-parametric method to estimate the Hubble constant as a function of redshift. We establish independent estimates of the evolution of Hubble constant by diagonalizing the covariance matrix. From type Ia supernovae, baryon acoustic oscillation data and the observed Hubble parameter data, a decreasing trend in the Hubble constant with a significance of a 5.6σ confidence level is found. At low redshift, its value is dramatically consistent with that measured from the local distance ladder and it drops to the value measured from the cosmic microwave background at high redshift. Our results may relieve the Hubble tension, with a preference for recent solutions, especially with respect to novel physics.

Unitary paradox of cosmological perturbations

If we interpret the Bekenstein–Hawking entropy of the Hubble horizon as thermodynamic entropy, then the entanglement entropy of the superhorizon modes of curvature perturbation entangled with the subhorizon modes will exceed the Bekenstein–Hawking bound at some point; we call this the unitary paradox of cosmological perturbations by analogy with black hole. In order to avoid a fine-tuned problem, the paradox must occur during the inflationary era at the critical time [Formula: see text] (in Planck units), where [Formula: see text] is the first Hubble slow-roll parameter and [Formula: see text] is the Hubble rate during inflation. If we instead accept the fine-tuned problem, then the paradox will occur during the dark energy era at the critical time [Formula: see text], where [Formula: see text] is the Hubble rate dominated by dark energy, [Formula: see text] is the total number of e-folds of inflation and [Formula: see text] is a purification factor that takes the range [Formula: see text].

BICEP/Keck. XVII. Line-of-sight Distortion Analysis: Estimates of Gravitational Lensing, Anisotropic Cosmic Birefringence, Patchy Reionization, and Systematic Errors

We present estimates of line-of-sight distortion fields derived from the 95 and 150 GHz data taken by BICEP2, BICEP3, and the Keck Array up to the 2018 observing season, leading to cosmological constraints and a study of instrumental and astrophysical systematics. Cosmological constraints are derived from three of the distortion fields concerning gravitational lensing from large-scale structure, polarization rotation from magnetic fields or an axion-like field, and the screening effect of patchy reionization. We measure an amplitude of the lensing power spectrum . We constrain polarization rotation, expressed as the coupling constant of a Chern–Simons electromagnetic term g a γ ≤ 2.6 × 10−2/H I , where H I is the inflationary Hubble parameter, and an amplitude of primordial magnetic fields smoothed over 1 Mpc B 1Mpc ≤ 6.6 nG at 95 GHz. We constrain the rms of optical depth fluctuations in a simple “crinkly surface” model of patchy reionization, finding A τ < 0.19 (2σ) for the coherence scale of L c = 100. We show that all of the distortion fields of the 95 and 150 GHz polarization maps are consistent with simulations including lensed ΛCDM, dust, and noise, with no evidence for instrumental systematics. In some cases, the EB and TB quadratic estimators presented here are more sensitive than our previous map-based null tests at identifying and rejecting spurious B-modes that might arise from instrumental effects. Finally, we verify that the standard deprojection filtering in the BICEP/Keck data processing is effective at removing temperature to polarization leakage.

Logarithmic inflation?

We consider a scalar–tensor action model, both simple and peculiar at the same time, with a boundary term added that it is form-invariant both under the conformal transformation of the metric as well as under the reparametrization of the scalar field. Under this assumption, the boundary term proposed matches (except factors) with the Gibbons–Hawking–York term proposed in such a way it cancels the term(s) involving [Formula: see text]. A matter term is added to the action also. In the Jordan frame, the pure gravitational action becomes the Einstein–Hilbert action with a cosmological constant when the scalar field takes the constant value of their vev, [Formula: see text], which is no otherwise but the only stable minimum of the classical potential chosen which is logarithmic type. This potential presents a large plateau in which it is almost fully flat and the decay of the field from its initial value (assumed to be close to [Formula: see text]) to vacuum draws a Low Field (or New Inflation) scenario. The model fits very well with the current paradigm of the universe and, under some assumptions, gives a good account of the value of the Higgs mass, the current value of the cosmological constant, e-folding, the Hubble parameter, the spectral index of scalar perturbations, etc. The model is not studied in Einstein’s frame. In this, only the expressions of the field and the potential, for a simple case, are achieved. As a result, we get that the nature of the decay of the initial value to its ground state for the scalar field, in this frame, should be by quantum tunneling and not by slow rolling.

Interacting DBI essence in viscous [formula omitted] gravity for different choices of scale factor and thermodynamics with power-law and logarithmic entropy corrections

From the hydrodynamic viewpoint, the inclusion of viscosity in the theory of cosmic fluid may appear as an abstraction. Using modern observational results for the Hubble parameter and standard Friedmann formalism, we may have a description of the universe up to the inflationary era, or we may be able to analyse the probable ultimate fate of the universe. Inspired by this bulk viscosity formalism reviewed in Brevik et al., (2017) in this work, we report a study of the DBI essence scalar field model of dark energy (DE) interacting with pressureless dark matter (DM) in the presence of bulk viscous pressure of the form ξ=ξ0+ξ1H+ξ2(Ḣ+H2). We choose the scale factor in three forms: emergent, logamediate, and intermediate. We choose the interaction term Q in the form Q=3HδρΛ, where ρΛ denotes the density of the scalar field model of DE. We present a detailed cosmology of the interacting DE and observe a quintom behaviour of the equation of state (EoS). We conduct a statefinder analysis to attain ΛCDM fixed point by the interacting DE. Subsequently, we report a reconstruction scheme for f(T) gravity. Finally, we conduct thermodynamic analysis where we consider entropy’s logarithmic and power-law corrections.

A parametric view of Hubble parameter for scalar field dark energy model

Abstract: In our present work, we have considered a simple parametric form of the Hubble parameter (H) for a canonical scalar field model described within a spatially flat FRW spacetime framework. Here we have considered a well-behaved parametrization scheme of the normalized Hubble parameter to explain the expansión history of the universe. Under this scenario, we have obtained the analytic solutions for various relevant cosmological parameters. We have also reconstructed the potential function V( φ) for the scalar field φ. It has been found that the deceleration parameter (q) shows exactly the nature which is well expected, i.e., an accelerated expansión for low z limit and deceleration for high z limit, which is essential for the structure formation of the Universe. Detailed data analysis has been carried out to check the viability of the proposed theoretical model by using combined dataset SNIa+H(z)+BAO/CMB and put constraints on the cosmological parameters, viz. the present value of the Hubble parameter H0.

H0=69.8±1.3 km s−1 Mpc−1 , Ωm0=0.288±0.017 , and other constraints from lower-redshift, non-CMB, expansion-rate data

We use updated Type Ia Pantheon+ supernova, baryon acoustic oscillation, and Hubble parameter (now also accounting for correlations) data, as well as new reverberation-measured C IV quasar data, and quasar angular size, H II starburst galaxy, reverberation-measured Mg II quasar, and Amati-correlated gamma-ray burst data to constrain cosmological parameters. We show that these data sets result in mutually consistent constraints and jointly use them to constrain cosmological parameters in six different spatially-flat and non-flat cosmological models. Our analysis provides summary model-independent determinations of two key cosmological parameters: the Hubble constant, $H_0=69.8\pm1.3$ $\rm{km \ s^{-1} \ Mpc^{-1}}$, and the current non-relativistic matter density parameter, $\Omega_{m0}=0.288\pm0.017$. Our summary error bars are 2.4 and 2.3 times those obtained using the flat $\Lambda$CDM model and Planck TT,TE,EE+lowE+lensing cosmic microwave background (CMB) anisotropy data. Our $H_0$ value is very consistent with that from the local expansion rate based on the Tip of the Red Giant Branch data, is 2$\sigma$ lower than that from the local expansion rate based on Type Ia supernova and Cepheid data, and is 2$\sigma$ higher than that in the flat $\Lambda$CDM model based on Planck TT,TE,EE+lowE+lensing CMB data. Our data compilation shows at most mild evidence for non-flat spatial hypersurfaces, but more significant evidence for dark energy dynamics, 2$\sigma$ or larger in the spatially-flat dynamical dark energy models we study.

Constrained f(Q,T) gravity accelerating cosmological model and its dynamical system analysis

In this paper, we have presented an accelerating cosmological model of the Universe in an extended symmetric teleparallel gravity or f(Q,T) gravity. The parametric form of the Hubble parameter is, H(z)=H0[α+(1−α)(1+z)n]32n, where H0 and n are constants and for n=3, the ΛCDM scenario can be obtained. We have considered the logarithmic form of f(Q,T) as, f(Q,T)=−Q+βlog⁡(QQ0)+γT, where β and γ are the free model parameters. Using the Hubble, Baryon Acoustic Oscillations (BAO), and Type Ia Supernovae (SNe Ia) datasets, the present value of the Hubble parameter and other free parameters are constrained. Further other cosmographic and dynamical parameters are presented using the obtained constrained values of the Hubble and free parameters. The model shows the quintessence behavior of the Universe at the present time. The present value of the EoS parameter is obtained as, ω0=−0.56 for the Hubble+BAO+SNe datasets. The energy conditions are presented and the violation of the strong energy condition has been shown. We have performed the dynamical system analysis to validate the stability of the model. From the evolutionary plot obtained through the dynamical system variables, the present values of density parameters have been obtained as Ωm≈0.3 and Ωde≈0.7.

Late-time dark energy and Hubble tension

AbstractWe extend Einstein’s theory of general relativity by introducing stochastic elements in addition to the usual fields and apply it to explore late-time redshift. The stochastic perturbation of spacetime enforces an effective minimum length (ML) to give us a cosmological constant naturally derived from the diffusive nature of spacetime and a redshift driven by both the geometry of spacetime as well as its diffusive nature. In this new theory, “dark energy” is the manifestation of fundamental uncertainty caused by ML of spacetime. The new theory converges to the minimalΛ\LambdaCDM model in the era after the Big Bang, when the geometry dominates over the diffusive character of spacetime. However, as the Hubble parameter decreases in value over time, there is a period during which the diffusive effects play an increasingly important role. For later times, as the universe approaches its minimum total energy density, the resulting redshift obtains significant contributions from both the geometry, captured by the Hubble parameter “HH,” and spacetime diffusion, captured by a new parameter “DD,” the diffusive equivalent toHH. Hence, the new theory presented here is particularly important during the later times in whichHHdiminishes and becomes comparable toDD. The theory suggests that the Hubble tension might be relieved by the diffusive character of spacetime. In order to compare the early time Hubble parameter estimates to the late-time estimates, we must recognize the contribution diffusion makes to the redshift observations and further reformulate luminosity distance and its kinematic expression to account for the effects of diffusion in addition to geometry. We perform a simple analysis of Type Ia supernovae observations with distances calibrated using Cepheids to obtain estimates for the new diffusion parameter. Based on these results, the new theory places the universe well inside a vacuum-dominated regime with a small and diminishing diffusion parameter.

The oscillatory universe, phantom crossing and the Hubble tension

We investigate the validity of cosmological models with an oscillating scale factor in relation to late-time cosmological observations. We show that these models not only meet the required late time observational constraints, but can also alleviate the Hubble tension. As a generic feature of the model, the Hubble parameter increases near the current epoch due to its cyclical nature exhibiting the phantom nature allowing to address the said issue related to late time acceleration.