Alexander S. Tepliakov

arXiv2026

Tsallis Holographic Dark Energy model with varying gravitational constant vs $Λ$CDM model: statistical analysis of observational data and tensions problem

We investigate the cosmological evolution of a flat Friedmann--Robertson--Walker Universe filled with Tsallis holographic dark energy (THDE) under the assumption that the gravitational constant $G$ varies with time according to the power-law parametrisation $d\ln G / d\ln a = α_G = \mathrm{const}$. In this framework, the holographic dark energy density is given by $ρ_{\mathrm{DE}} \propto L^{2γ- 4}$, where $L$ is the future event horizon and $γ$ is the Tsallis non-additivity parameter. We study both the past and future evolution of the Universe for various values of the model parameters $C$, $γ$, and $α_G$. The viability of the model is tested against a combination of observational data, including the Pantheon+ Type Ia supernova sample, direct Hubble parameter measurements $H(z)$, and baryon acoustic oscillation (BAO) data. Using Markov Chain Monte Carlo (MCMC) methods and Bayesian analysis tools such as the Deviance Information Criterion (DIC), the Bayes factor, and the suspiciousness metric, we perform a rigorous statistical comparison with the standard $Λ$CDM model. Our results show that models with a varying gravitational constant are preferred over $Λ$CDM. The best fit to the combined data is obtained for the THDE model with $C < 1$. Furthermore, we analyse the internal consistency of the data sets using the Index of Inconsistency, the $Q_{\mathrm{DMAP}}$ statistic, and Bayesian suspiciousness. We find that the THDE model with varying $G$ and $C < 1$ partially alleviates the tensions between different probes, reducing the significance from $\sim 7.4σ$ to $\sim 5.3σ$.

physics.gen-ph↗

arXiv2025

Non-flat Universe with Tsallis holographic dark energy

We investigated evolution of metric and density perturbations for Tsallis model of holographic dark energy with energy density $\sim L^{2γ- 4}$, where $L$ is length of event horizon or inverse Hubble parameter and $γ$ is parameter of non-additivity close to $1$. Because holographic dark energy is not an ordinary cosmological fluid but a phenomena caused by boundaries of the universe, the ordinary analysis for perturbations is not suitable. One needs to consider perturbations of the future event horizon. For realistic values of parameters it was discovered that perturbations of dark energy don't grow infinitely but vanish or freeze. We also considered the case of realistic interaction between holographic dark energy and matter and showed that in this case perturbations also can asymptotically freeze with time.

gr-qc↗

arXiv2024

General constraints on Tsallis holographic dark energy from observational data

We investigated Tsallis holographic dark energy (THDE) model in light of modern observations of supernovae, Hubble parameter measurements, data for baryon acoustic oscillations and fluctuations of matter density. The dark energy density for THDE model is written as $ρ_d = 3C^2 / L^{4-2γ}$ where $C$ and $γ$ are some constants. Scale $L$ is infrared cut-off lenght for which we use the event horizon. For analysis of type Ia supernovae (SNeIa) data Pantheon+ samples are involved. Dark Energy Spectroscopic Instrument (DESI) 2024 measurements serves as source of data about ratios between sound horizon $r_d$ and Hubble ($d_H$) or volume averaged ($d_V$) distances. The updated dataset of Hubble parameter for various redshift is also used in our analysis. Finally we considered the dependence of matter density fluctuations in past from redshift. The standard stratefy of $χ^2$ minimizing allows to estimate the optimal values of parameters ($Ω_{de}$ and $H_0$) for some fixed values of $C$ and $γ$. One note that best-fit values for parameters $H_0$ from Hubble parameter and SNeIa data are more close than in standard $Λ$CDM model for some $C$ and $γ$ although problem of Hubble tension remains unsolved. The combined data analysis also gives slightly better results in comparison with standard cosmology. We included in our consideration the possible interaction between matter and holographic component and estimated the acceptable interval of model parameters in this case.

astro-ph.CO↗

arXiv2024

Evolution of perturbations in the model of Tsallis holographic dark energy

We investigated evolution of metric and density perturbations for Tsallis model of holographic dark energy with energy density $\sim L^{2γ- 4}$, where $L$ is length of event horizon or inverse Hubble parameter and $γ$ is parameter of non-additivity close to $1$. Because holographic dark energy is not an ordinary cosmological fluid but a phenomena caused by boundaries of the universe, the ordinary analysis for perturbations is not suitable. One needs to consider perturbations of the future event horizon. For realistic values of parameters it was discovered that perturbations of dark energy don't grow infinitely but vanish or freeze. We also considered the case of realistic interaction between holographic dark energy and matter and showed that in this case perturbations also can asymptotically freeze with time.

gr-qc↗

arXiv2022

Tsallis holographic dark energy model with event horizon cutoff in modified gravity

We considered the Tsallis holographic dark energy model in frames of Nojiri-Odintsov gravity with $f(R)=R+λR^2-σμ/{R}$. For IR cutoff event horizon is taken. The cosmological evolution of such universe is investigated for various initial conditions and values of parameters. The dependence of the Hubble parameter $H$ from time in the future has an oscillations. It is shown that for $μ\neq 0$ appearance of singularities are typical and the time up to these singularities can be relatively small from cosmological viewpoint. The singularity is associated with the zero of second deribative of $f(R)$ on $R$. It is interesting to note that these models can describe observational data from Ia supernovae astrophysics and dependence of the Hubble parameter from redshift $z$ at least not worse than canonical $Λ$CDM model.

gr-qc↗

arXiv2022

Crossing of phantom divide line in model \\of interacting Tsallis holographic dark energy

We consider a Tsallis holographic dark energy model with interaction between dark energy and matter. The density of dark energy is taken as $ρ_d \sim 3C^2/L^{4-2γ}$, where $C$, $γ$ are constants. The event horizon is chosen as the characteristic scale $L$. The cosmological dynamics of the universe are analyzed, with special attention paid to the possibility of crossing the phantom line $w_{eff}=-1$. It is shown that for certain values of parameters this may occur not only once, but also twice.

gr-qc↗

arXiv2019

Some models of holographic dark energy on the Randall-Sundrum brane and observational data

The some models of holographic dark energy for Randall-Sandrum brane are considered. For first class of dark energy models we take energy density in form $\sim L^{2γ-4}$ where $L$ is size of events horizon in Universe and $γ$ is parameter (Tsallis holographic energy). Analysis of observational data allows to define upper limit on value of $δ=ρ_{0}/2λ$ ($ρ_{0}$ is current energy density in the Universe and $λ$ is brane tension). Then we investigate models for which dark energy density has form $ρ_{de}=C^{2}L^{-2}-C_{1}^{2}H^{2}$ where $H$ is Hubble parameter.

gr-qc↗