arXiv subjects

Hussain Gohar

Publications and source records attributed to Hussain Gohar.

14 recordsLinked to original sources

arXiv2026

Modified Cosmology from Mass-to-Horizon Relation: Observational Bounds

We constrain the class of modified cosmologies derived in Paper I [1] from a generalized mass-to-horizon relation (MHR) that enforces thermodynamic consistency between the Cai-Kim horizon temperature and generalized horizon entropies. The modified Friedmann equations depend on an entropy exponent $m$, an MHR coupling parameter $γ$, and an entanglement-correction amplitude $f_B$, with standard $Λ$CDM recovered in the appropriate limit. Using Pantheon$+$/SH0ES Type~Ia supernovae, cosmic chronometers, DESI DR2 baryon acoustic oscillations, and Planck 2018 CMB distance priors, we constrain eight physically motivated sub-cases via Markov chain Monte Carlo and compare models through the Bayesian log-evidence. The entropy exponent is tightly bounded, $|m-1|\lesssim O(10^{-4})$ when the MHR coupling is fixed ($γ=1$), relaxing to $O(10^{-3})$ along the $m$-$γ$ degeneracy, excluding any macroscopically significant departure from standard horizon thermodynamics. Freeing the MHR coupling parameter or the entanglement amplitude raises the inferred Hubble constant to $h\simeq0.70$-$0.71$, reducing the CMB-SH0ES tension from ${\sim}4σ$ to ${\sim}1.2$-$2.6σ$, but no scenario fully resolves it within a flat universe. The Bayesian log-evidence nevertheless disfavors every extension relative to $Λ$CDM in all dataset combinations ($-16\lesssimΔ\ln Z \lesssim-1$): the improved fits obtained when the SH0ES calibration is included reflect an absorption of the Hubble tension by the additional parameters rather than genuine evidence for modified horizon entropy.

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arXiv2026

Modified Cosmology from Mass-to-Horizon Relation: Background Evolution

We investigate the cosmological implications of the mass-to-horizon relation, which provides a unified framework for thermodynamically consistent generalized horizon-entropy functionals. Using the Cai-Kim formulation of the first law of thermodynamics, we derive the corresponding modified Friedmann equations and examine the resulting background evolution. We find that cosmological viability sharply restricts admissible deviations from the Bekenstein-Hawking area law: phenomenologically acceptable scenarios are confined to a narrow neighborhood of the standard entropy, while more pronounced deviations generically spoil the standard radiation-matter-dark-energy sequence. Power-law entanglement corrections can give rise to a moderate early-dark-energy component, but only within a tightly constrained region of parameter space, whereas quantum-gravity corrections are suppressed by the Planck scale and remain observationally irrelevant. Consequently, all viable models predict a $Λ$CDM-like cosmological background at the present epoch. These findings demonstrate that background cosmology alone imposes stringent constraints on thermodynamically consistent generalized entropy constructions of this class.

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arXiv2026

Scalar-Tensor Gravity as a Probe of Generalized Black Hole Entropy

We develop a geometric realization of a broad class of generalized black hole entropy functionals by establishing their direct correspondence with the Misner$-$Sharp quasilocal mass and the Wald Noether$-$charge entropy in scalar$-$tensor theories of gravity. The resulting models feature a scale-dependent effective gravitational coupling, whose functional dependence is determined by the underlying entropy parameters. Within this framework, we derive explicit Einstein-frame scalar potentials: for Barrow entropy, a steep exponential potential; for Tsallis$-$Cirto entropy, an exponential potential governed by the nonextensivity parameter; and for quantum-gravity and entanglement$-$induced corrections, an approximately linear potential. These distinct potentials generate characteristic cosmological phenomenology, with implications for inflationary dynamics, late-time dark-energy behavior, and non-singular bouncing cosmologies. The framework is compatible with current constraints from solar-system tests, big-bang nucleosynthesis, and pulsar-timing observations, and it yields predictions that can be probed by forthcoming observational surveys. In this way, the analysis establishes a unified and geometrically grounded connection between information$-$theoretic entropy proposals and gravitational field theory.

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arXiv2026

Addressing the Hubble Tension: Insights from Reversible and Irreversible Thermodynamic Processes

We investigate reversible and irreversible thermodynamic processes in cosmology and their impact on the Hubble tension. Gravitationally induced adiabatic matter creation/annihilation is treated as irreversible, while energy exchange between the cosmic bulk and horizon is modeled as reversible. Two scenarios are proposed: Model I features matter creation/annihilation across all species with energy transfer to effective entropic dark energy; Model II considers dark matter creation/annihilation with energy flow from baryonic matter and radiation. The creation rate is parameterized as $Γ(t)=Γ_0 H$, with energy transfer controlled by $γ$. We constrain both models using Pantheon$+$ supernovae, CMB distance priors, baryon acoustic oscillations, gamma-ray bursts, and cosmic chronometers, with and without SH$_0$ES. When SH$_0$ES is included, matter annihilation ($Γ_0<0$) is statistically preferred, yielding $H_0 = 71.75 \pm 0.79$ km s$^{-1}$ Mpc$^{-1}$ (Model I) and $H_0 = 71.06 \pm 0.81$ km s$^{-1}$ Mpc$^{-1}$ (Model II), corresponding to $1.2σ$ and $1.8σ$ consistency with the SH$_0$ES value $73.17 \pm 0.86$ km s$^{-1}$ Mpc$^{-1}$. Matter creation ($Γ_0>0$) or pure energy flow ($Γ=0$) do not improve the tension. Without SH$_0$ES, information criteria show no preference over $Λ$CDM. For the matter annihilation/creation with energy flow, the effective entropic dark energy evolves dynamically, mimicking radiation and matter before recombination and approaching a cosmological constant at late times. These results demonstrate that thermodynamically motivated interactions can alleviate the Hubble tension when calibrated with local measurements, while remaining consistent with cosmological data.

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arXiv2026

Mass-to-Horizon Entropic Cosmology: A Unified Thermodynamic Pathway to Cosmic Acceleration

We investigate the observational tests of generalized mass-to-horizon entropic cosmology by incorporating large-scale structure growth data in addition to purely geometric probes. The theoretical framework is constructed from a generalized mass-to-horizon scaling relation, $M \propto L^n$, which implies a corresponding generalized entropic functional $S_n \propto L^{n+1}$. Within this setting, cosmic acceleration arises as an emergent phenomenon driven by an entropic force acting on the cosmological horizon. While earlier studies demonstrated that these entropic cosmologies can reproduce the background expansion history of the standard $Λ$CDM model, here we present a comprehensive observational analysis that jointly employs Pantheon+ Type Ia supernova data with SH0ES calibration, DESI DR2 baryon acoustic oscillation measurements, cosmic microwave background (CMB) distance priors, and a suite of cosmological structure growth observations. A Bayesian model comparison indicates that the entropic models are statistically preferred over the conventional $Λ$CDM scenario, thereby providing strong support for an entropic origin of the observed late-time cosmic acceleration in place of a fundamental cosmological constant.

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arXiv2025

Mass-to-Horizon Relation and Entropy Beyond the Bekenstein-Hawking Limit

We introduce a generalized mass-horizon relation applicable to cosmological horizons. This formulation provides a unified framework for deriving a broad class of Bekenstein entropy extensions motivated by statistical mechanics, quantum gravity, and phenomenological considerations, through the application of the Clausius relation together with the Hawking temperature. We further introduce this notion as a foundational framework for constructing generalized entropy forms that remain consistent with thermodynamic laws and the holographic principle.

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arXiv2024

A generalized mass-to-horizon relation: a new global approach to entropic cosmologies and its connection to $Λ$CDM

In this letter, we propose a new generalized mass-to-horizon relation to be used in the context of entropic cosmologies and holographic principle scenarios. We show that a general scaling of the mass with the Universe horizon as $M=γ\frac{c^2}{G}L^n$ leads to a new generalized entropy $S_n = γ\frac{n}{1+n}\frac{2 π\,k_B\,c^3}{G\,\hbar} L^{n+1}$ from which we can recover many of the recently proposed forms of entropies at cosmological and black hole scales and also establish a thermodynamically consistent relation between each of them and Hawking temperature. We analyse the consequences of introducing this new mass-to-horizon relation on cosmological scales by comparing the corresponding modified Friedmann, acceleration, and continuity equations to cosmological data. We find that when $n=3$, the entropic cosmology model is fully and totally equivalent to the standard $Λ$CDM model, thus providing a new fundamental support for the origin and the nature of the cosmological constant. In general, if $\log γ< -3$, and irrespective of the value of $n$, we find a very good agreement with the data comparable with $Λ$CDM from which, in Bayesian terms, our models are indistinguishable.

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arXiv2024

On the foundations of entropic cosmologies: inconsistencies, possible solutions and dead end signs

In this letter we explore the foundations of entropic cosmology and highlight some important flaws which have emerged and adopted in the recent literature. We argue that, when applying entropy and temperature on the cosmological horizon by assuming the holographic principle for all thermodynamic approaches to cosmology and gravity, one must derive the consistent thermodynamic quantities following Clausius relation. One key assumption which is generally overlooked, is that in this process one must assume a mass-to-horizon relation, which is generally taken as a linear one. We show that, regardless of the type of entropy chosen on the cosmological horizon, when a thermodynamically consistent corresponding temperature is considered, all modified entropic force models are equivalent to and indistinguishable from the original entropic force models based on standard Bekenstein entropy and Hawking temperature. As such, they are also plagued by the same problems and inability to describe in a satisfactory qualitative and quantitative way the cosmological dynamics as it emerges from the probes we have. We also show that the standard accepted parameterization for Hawking temperature (including a $γ$ rescaling) is actually not correctly applied, namely, it is not related to entropy in a thermodynamically consistent way. Finally, we clearly state that the explicit form of the entropic force on cosmological horizons is mostly dictated by the assumption on the mass-to-horizon relation. As such, we discuss what should be done in order to fix all such issues, and what conceptually could be implied by its correct implementation in order to advance in the field.

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arXiv2023

Generalized Uncertainty Principle Impact on Nonextensive Black Hole Thermodynamics

The effect of the generalized uncertainty principle (GUP) on nonextensive thermodynamics applied to black holes, as well as the sparsity of the radiation at different temperatures associated with each nonextensive entropy, is investigated. We examine the Rényi, Tsallis-Cirto, Kaniadakis, Sharma Mittal, and Barrow entropies, temperatures, and heat capacities and show that, in each case, due to GUP corrections, the temperature and entropy have finite values, implying that the final state of the black hole is a remnant at the end of the evaporation process and that the sparsity of the radiation for massless bosons at each temperature depends on the mass of the black hole. We also find that GUP reduces the value of the sparsity profile for each case as compared to the sparsity parameter at Hawking temperature, which is always constant throughout the evaporation.

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arXiv2023

Equilibrium Temperature for Black Holes with Nonextensive Entropy

Hawking temperature has been widely utilised in the literature as the temperature that corresponds to various nonextensive entropies. In this study, we analyze the compatibility of the Hawking temperature with the nonextensive entropies. We demonstrate that, for every nonextensive entropy, one may define an effective temperature (which we call equilibrium temperature) by utilizing the equilibrium condition, and that there is always an additive equilibrium entropy associated with this effective temperature. Except for Bekenstein entropy, we show that Hawking temperature is thermodynamically inconsistent with other nonextensive entropies. We focus on the equilibrium requirement for the Tsallis-Cirto black hole entropy and demonstrate that the Bekenstein-Hawking entropy is the related equilibrium entropy, and the Hawking temperature is the associated equilibrium temperature for the Tsallis-Cirto black hole entropy.

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arXiv2021

Nonextensive Black Hole Entropy and Quantum Gravity Effects at the Last Stages of Evaporation

We analyze the Generalized Uncertainty Principle (GUP) impact onto the nonextensive black hole thermodynamics by using Rényi entropy. We show that when introducing GUP effects, both Rényi entropy and temperature associated to black holes have finite values at the end of the evaporation process. We also study the sparsity of the radiation, associated with Rényi temperature, and compare it with the sparsity of Hawking radiation. Finally, we investigate GUP modifications to the sparsity of the radiation when GUP effects are introduced into Rényi temperature.

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arXiv2020

Cosmological Constraints on Entropic Cosmology with Matter Creation

We investigate entropic force cosmological models with the possibility of matter creation and energy exchange between the bulk and the horizon of a homogeneous and an isotropic flat Universe. We consider three different kinds of entropy, Bekenstein's, the non-extensive Tsallis-Cirto's and the quartic entropy, plus some phenomenological functional forms for matter creation rate to model different entropic force models and put the observational constraints on them. We show that while most of them are basically indistinguishable from a standard $Λ$CDM scenario, the Bekenstein entropic force model with a matter creation rate proportional to the Hubble parameter is statistically highly favored over $Λ$CDM. As a general result, we also find that both the Hawking temperature parameter $γ$, which relates the energy exchange between the bulk and the boundary of the Universe, and the matter creation rate $Γ(t)$, must be very small in order to reproduce observational data.

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arXiv2018

Minimal length and the flow of entropy from black holes

The existence of a minimal length, predicted by different theories of quantum gravity, can be phenomenologically described in terms of a generalized uncertainty principle. We consider the impact of this quantum gravity motivated effect onto the information budget of a black hole and the sparsity of Hawking radiation during the black hole evaporation process. We show that the information is not transmitted at the same rate during the final stages of the evaporation and that the Hawking radiation is not sparse anymore when the black hole approaches the Planck mass.

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arXiv2018

Generalized uncertainty principle impact onto the black holes information flux and the sparsity of Hawking radiation

We investigate the generalized uncertainty principle (GUP) corrections to the entropy content and the information flux of black holes, as well as the corrections to the sparsity of the Hawking radiation at the late stages of evaporation. We find that due to these quantum gravity motivated corrections, the entropy flow per particle reduces its value on the approach to the Planck scale due to a better accuracy in counting the number of microstates. We also show that the radiation flow is no longer sparse when the mass of a black hole approaches Planck mass which is not the case for non-GUP calculations.

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