We have considered a spatially flat, homogeneous and isotropic FLRW Universe filled with a single fluid, known as logotropic dark fluid (LDF), whose pressure evolves through a logarithmic equation of state. We use the recent Pantheon SNIa and cosmic chronometer datasets to constrain the parameters of this model, the present fraction of dark matter $Ω_{m0}$ and the Hubble constant $H_0$. We find that the mean values of these parameters are $Ω_{m0}=0.288\pm 0.012$ and $H_{0}=69.652\pm 1.698~{\rm km/s/Mpc}$ at the $1σ$ CL. We also find that the LDF model shows a smooth transition from the deceleration phase to acceleration phase of the universe in the recent past. We notice that the redshift of this transition $z_{t}=0.706\pm 0.048$ ($1σ$ error) and is well consistent with the present observations. Interestingly, we find that the Universe will settle down to a $Λ$CDM model in future and there will not be any future singularity in the LDF model. Furthermore, we notice that there is no significant difference between the LDF and $Λ$CDM models at the present epoch, but the difference (at the percent level) between these models is found as the redshift increases. We have also studied the generalized second law of thermodynamics at the dynamical apparent horizon for the LDF model with the Bekenstein and Viaggiu entropies.
We show that the Einstein field equations with a negative cosmological constant can admit black hole solutions whose thermodynamics coincides with that of logotropic fluids, recently investigated to heal some cosmological and astrophysical issues. For this purpose, we adopt the Anton-Schmidt equation of state, which represents a generalized version of logotropic fluids. We thus propose a general treatment to obtain an asymptotic anti-de Sitter metric, reproducing the thermodynamic properties of both Anton-Schmidt and logotropic fluids. Hence, we explore how to construct suitable spacetime func…
We consider the possibility that the universe is made of a single dark fluid described by a logotropic equation of state $P=A\ln(ρ/ρ_*)$, where $ρ$ is the rest-mass density, $ρ_*$ is a reference density, and $A$ is the logotropic temperature. The energy density $ε$ is the sum of two terms: a rest-mass energy term $ρc^2$ that mimics dark matter and an internal energy term $u(ρ)=-P(ρ)-A$ that mimics dark energy. This decomposition leads to a natural, and physical, unification of dark matter and dark energy, and elucidates their mysterious nature. The logotropic model depends on a single paramete…
We perform a detailed comparison between the Logotropic model [P.H. Chavanis, Eur. Phys. J. Plus 130 (2015) 130] and the $Λ$CDM model. These two models behave similarly at large (cosmological) scales up to the present. Differences will appear only in the far future, in about $25\, {\rm Gyrs}$, when the Logotropic Universe becomes phantom while the $Λ$CDM Universe enters in the de Sitter era. However, the Logotropic model differs from the $Λ$CDM model at small (galactic) scales, where the latter encounters serious problems. Having a nonvanishing pressure, the Logotropic model can solve the cusp…
We here study extended classes of logotropic fluids as \textit{unified dark energy models}. Under the hypothesis of the Anton-Schmidt scenario, we consider the universe obeying a single fluid whose pressure evolves through a logarithmic equation of state. This result is in analogy with crystals under isotropic stresses. Thus, we investigate thermodynamic and dynamical consequences by integrating the speed of sound to obtain the pressure in terms of the density, leading to an extended version of the Anton-Schmidt cosmic fluids. Within this picture, we get significant outcomes expanding the Anto…
We propose a heuristic unification of dark matter and dark energy in terms of a single dark fluid with a logotropic equation of state $P=A\ln(ρ/ρ_P)$, where $ρ$ is the rest-mass density, $ρ_P$ is the Planck density, and $A$ is the logotropic temperature. The energy density $ε$ is the sum of a rest-mass energy term $ρc^2$ mimicking dark matter and an internal energy term $u(ρ)=-P(ρ)-A$ mimicking dark energy. The logotropic temperature is approximately given by $A \simeq ρ_Λc^2/\ln(ρ_P/ρ_Λ)\simeqρ_Λc^2/[123 \ln(10)]$, where $ρ_Λ$ is the cosmological density. More precisely, we obtain $A=2.13\tim…
In a previous paper we have introduced a new cosmological model that we called the logotropic model. The logotropic model is able to account, without free parameter, for the constant surface density of the dark matter halos, for their mass-radius relation, and for the Tully-Fisher relation. In this paper, we explore other consequences of this model. By advocating a form of "strong cosmic coincidence" we predict that the present proportion of dark energy in the Universe is $Ω_{\rm de,0}=e/(1+e)\simeq 0.731$ which is close to the observed value. We also remark that the surface density of dark ma…
In this paper, we study the model of $f(T, B)$ gravity with viscous fluid in flat-FRW metric, in which $T$ and $B$ are torsion scalar and boundary term, respectively. We obtain the Friedmann equations in the framework of modified teleparallel gravity by tetrad components. We consider an interacting model between matter and dark energy so that universe dominates by viscous fluid. Then, we write the corresponding cosmological parameters in terms of the redshift parameter, and, we parameterize the Hubble parameter with experimental data. In what follows, we plot the corresponding cosmological par…
A significant observational effort has been directed to unveil the nature of the so-called dark energy. However, given the large number of theoretical possibilities, it is possible that such a task cannot be performed on the basis only of the observational data. In this article we discuss some thermodynamic properties of this energy component by assuming that its constituents are massless quanta with a general time-dependent equation-of-state parameter $ω(z)=ω_0 + ω_a f(z)$, where $ω_0$ and $ω_a$ are constants and $f(z)$ may assume different forms. We show that very restrictive bounds can be p…
The thermodynamics-gravity conjecture reveals that one can derive the gravitational field equations by using the first law of thermodynamics and vice versa. Considering the entropy associated with the horizon in the form of non-extensive Tsallis entropy, $S\sim A^β$ here we first derive the corresponding gravitational field equations by applying the Clausius relation $δQ=T δS$ to the horizon. We then construct the Friedmann equations of Friedmann-Lemaître-Robertson-Walker (FLRW) universe based on Tsallis modified gravity (TMG). Moreover, in order to constrain the cosmological parameters of TMG…
Particle creation (or annihilation) mechanisms, described by either quantum field theoretical models, or by the thermodynamics of irreversible processes, play an important role in the evolution of the early Universe, like, for example, in the warm inflationary scenario. Following a similar approach, based on the thermodynamics of open systems, in the present work we investigate the consequences of the interaction, decay, and particle generation in a many-component Universe, containing dark energy, dark matter, radiation, and ordinary matter, respectively. In this model, due to the interaction …
We apply the holographic principle in the cosmological context through the nonadditive Tsallis entropy, used to describe the thermodynamic properties of nonstandard statistical systems such as the gravitational ones. Assuming the future event horizon as the infrared cutoff, we build a dark energy model free from cosmological inconsistencies, which includes standard thermodynamics and standard holographic dark energy as a limiting case. We thus describe the dynamics of Tsallis holographic dark energy in a flat FLRW background. Hence, we investigate cosmological perturbations in the linear regim…
Observational and Thermodynamic aspects of one-dimensional Dark Energy EoS parametrization models
Institute of Fundamental Physics and Quantum Technology, Department of Physics, School of Physical Science and Technology, Ningbo University（宁波大学物理科学与技术学院基础物理与量子技术研究所）
Recently, we have investigated the dynamics of the universe in tachyon cosmology with non-minimal coupling to matter \cite{faraj}-\cite{faraj3}. In particular, for the interacting holographic dark energy (IHDE), the model is studied in \cite{Ravanpak}. In the current work, a significant observational program has been conducted to unveil the model's thermodynamic properties. Our result shows that the IHDE version of our model better fits the observational data than $Λ$CDM model. The first and generalized second thermodynamics laws for the universe enveloped by cosmological apparent and event ho…
We propose a model-independent parametrization of dark energy motivated by thermodynamics. To this aim, we consider Padé polynomials to reconstruct the form of deceleration parameter adequate to describe different epochs of cosmic history and divergence-free in the far future. The proposed scenario also fulfills the demand of structure formation and contains the $Λ$CDM model as a limiting case. Thus, a numerical analysis at both background and perturbation levels is performed through the Markov Chain Monte Carlo method in view of the most recent cosmic data. We then use the observational const…
In this paper, the generalized second law (GSL) of thermodynamics and entropy is revisited in the context of cosmological models in Gauss-Bonnet gravity with the boundary of the universe is assumed to be enclosed by the dynamical apparent horizon. The model is best fitted with the observational data for distance modulus. The best fitted geometric and thermodynamic parameters such as equation of state parameter, deceleration parameter and entropy are derived. To link between thermodynamic and geometric parameters, the "entropy rate of change multiplied by the temperature" as a model independent…
In this paper we have investigated the limits imposed by thermodynamics on a dark energy fluid. We have obtained the heat capacities and the compressibilities for a dark energy fluid. The thermal and mechanical stabilities require these quantities to be positive. We have shown that dark energy fluids must satisfy the stability conditions and that such requirement put difficulties in the cosmic fluid models with negative constant EoS parameters. We have also shown that the observational constraints imposed by SN Ia, BAO and $H(z)$ data on a general dark energy fluid with a time-dependent EoS pa…
Physical limits on the equation-of-state (EoS) parameter of a dark energy component non-minimally coupled with the dark matter field are examined in light of the second law of thermodynamics and the positiveness of entropy. Such constraints are combined with observational data sets of type Ia supernovae, baryon acoustic oscillations and the angular acoustic scale of the cosmic microwave background to impose restrictions on the behaviour of the dark matter/dark energy interaction. Considering two EoS parameterisations of the type $w = w_0 + w_aζ(z)$, we derive a general expression for the evolu…
Kruglov-entropy cosmology from apparent-horizon thermodynamics: background dynamics and observational constraints
The Institute for Fundamental Study “The Tah Poe Academia Institute”, Naresuan University（那莱苏安大学基础研究院“塔波学术院”）；NAS, Centre for Theoretical Physics & Natural Philosophy, Mahidol University（马希隆大学自然与科学研究中心理论物理与自然哲学中心）；Department of Physics, Naresuan University（那莱苏安大学物理系）
It is argued that the discovery of cosmic acceleration could have been anticipated on thermodynamic grounds, namely, the generalized second law and the approach to equilibrium at large scale factor. Therefore, the existence of dark energy -or equivalently, some modified gravity theory- should have been expected. In general, cosmological models that satisfy the above criteria show compatibility with observational data.
Viscous Ghost Dark Energy in $f(Q, L_m)$ Gravity: Observational and Thermodynamic Validity
School of Technology Management & Engineering, SVKM’s NMIMS (Deemed to be University)（SVKM's NMIMS（认定大学）技术与工程学院）；Department of Mathematics, Maharaja Agrasen University（Maharaja Agrasen 大学数学系）
Thermodynamic implications and observational constraints of interacting $f(Q,\mathcal{T})$ gravity in FRW Universe
S.P.M. Science and Gilani Arts, Commerce College（S.P.M. 科学与吉拉尼艺术商业学院）；L N Gumilyov Eurasian National University（L.N. 古米廖夫欧亚国立大学）；Pacif Institute of Cosmology and Selfology (PICS)（Pacif 宇宙学与自我学研究所（PICS））；Government Vidarbha Institute of Science and Humanities（政府维达尔巴科学与技术人文学院）；Maharaja Agrasen University（玛哈拉贾·阿格拉森大学）；Government college of Arts and Science, Chh. Sambhajinagar（Chh. 桑巴吉纳加尔艺术与科学学院）
We investigate various scenarios which include interaction forms between dark matter and dark energy that exhibit sign reverse, namely where the transfer of energy between the dark fluids changes sign during evolution. We study the large-scale inhomogeneities in such interacting scenarios and we confront them with the latest astronomical data. Our analysis shows that the sign-changeable interaction models are able to produce stable perturbations. Additionally, the data seem to slightly favor a non-zero interaction, however, within $1σ$ confidence level (CL) the scenarios cannot be distinguishe…
The thermodynamic and dynamical properties of a variable dark energy model with density scaling as rho_x \propto (1+z)^m, z being the redshift, are discussed following the outline of Jetzer et al. This kind of models are proven to lead to the creation/disruption of matter and radiation, which affect the cosmic evolution of both matter and radiation components in the Universe. In particular, we have concentrated on the temperature-redshift relation of radiation, which has been constrained using a very recent collection of cosmic microwave background (CMB) temperature measurements up to z ~ 3. F…
Thermodynamics, thermodynamic geometry, and the shadow of a Bardeen black hole surrounded by a Kiselev fluid: the role of regularity, asymptotics, and observational self-consistency
Branch structure and nonextensive thermodynamics of Kalb-Ramond-ModMax black holes: observational signatures
Eastern Mediterranean University（东地中海大学）；National Observatory of Athens（雅典国家天文台）；Universidad Católica del Norte（北天主教学会）；University of Science and Technology of China（中国科学技术大学）
Null Geodesics, Thermodynamics, Weak Gravitational Lensing, and Black Hole Shadow Characteristics of a Frolov Regular Black Hole with Constraints from EHT Observations
Is Dark Energy an Effective Manifestation of Non-equilibrium Thermodynamics? -- Insights from DESI
Indian Statistical Institute（印度统计研究所）；Presidency University（总统大学）；Universitat Politècnica de Catalunya（加泰罗尼亚理工大学）；Durban University of Technology（德班理工大学）；National Observatory of Athens（雅典国家天文台）；Universidad Católica del Norte（北天主教学会大学）；University of Science and Technology of China（中国科学技术大学）
The present work deals with a detailed study of universal thermodynamics in different modified gravity theories. The validity of the generalized second law of thermodynamics (GSLT) and thermodynamical equilibrium (TE) of the Universe bounded by a horizon (apparent/event) in f(R)-gravity, Einstein-Gauss-Bonnet gravity, RS-II brane scenario and DGP brane model has been investigated. In the perspective of recent observational evidences, the matter in the Universe is chosen as interacting holographic dark energy model. The entropy on the horizons are evaluated from the validity of the unified firs…
Recent observational evidences claim an accelerating expansion of the universe at present epoch. It is commonly incorporated in standard cosmology by the introduction of an exotic matter (that violates the strong energy condition) known as dark energy (DE). As event horizon exists for accelerating universe so there has been a lot of work on universal thermodynamics (i.e., thermodynamics of the universe bounded by apparent or event horizon). Recently, thermodynamical equilibrium has been examined for both the horizons. In the present work we show that universal thermodynamics with event horizon…
Here we are trying to find the conditions for the validity of the generalized second law of thermodynamics (GSLT) assuming the first law of thermodynamics on the event horizon in both cases when the FRW universe is filled with interacting two fluid system- one in the form of cold dark matter and the other is either holographic dark energy or new age graphic dark energy. Using the recent observational data we have found that GSLT holds both in quintessence era as well as in phantom era for new age graphic model while for holographic dark energy GSLT is valid only in phantom era.
We construct modified cosmological scenarios through the application of the first law of thermodynamics in the universe horizon, but using the generalized, nonextensive Tsallis entropy instead of the usual Bekenstein-Hawking one. We result to modified cosmological equations that possess the usual ones as a particular limit, but which in the general case contain extra terms that appear for the first time, that constitute an effective dark energy sector quantified by the nonextensive parameter $δ$. When the matter sector is dust, we extract analytical expressions for the dark energy density and …
In what follows, we investigate the relation between the Friedmann and thermodynamic pressure equations, through solving the Friedmann and thermodynamic pressure equations simultaneously. Our investigation shows that a perfect fluid, as a suitable solution for the Friedmann equations leading to the standard modelling of the universe expansion history, cannot simultaneously satisfy the thermodynamic pressure equation and those of Friedmann. Moreover, we consider various energy definitions, such as the Komar mass, and solve the Friedmann and thermodynamic pressure equations simultaneously to get…
In this paper we study the consistency of a cosmological model representing a universe filled with a one-component dissipative dark matter fluid, in the framework of the causal Israel-Stewart theory, where a general expression arising from perturbation analysis for the relaxation time $τ$ is used. This model is described by an exact analytic solution recently found in [N. Cruz, E. González and G. Palma, Gen. Rel. Grav. \textbf{52}, 62 (2020), which depends on several model parameters as well as integration constants, allowing the use of Type Ia Supernovae and Observational Hubble data to perfo…
A new cosmic scenario with gravitationally induced particle creation is proposed. In this model the Universe evolves from an early to a late time de Sitter era, with the recent accelerating phase driven only by the negative creation pressure associated with the cold dark matter component. The model can be interpreted as an attempt to reduce the so-called cosmic sector (dark matter plus dark energy) and relate the two cosmic accelerating phases (early and late time de Sitter expansions). A detailed thermodynamic analysis including possible quantum corrections is also carried out. For a very wid…
This paper investigates a newly proposed fluid description of dark energy within the framework of the late-time accelerated expansion of the universe. Our primary objective is to explore the theoretical foundation of the proposed equation of state by establishing its correspondence with well-known scalar field models such as quintessence, k-essence, and DBI-essence. Through this correspondence, we reconstruct key field parameters, including the scalar field $ϕ$ and scalar potential $V(ϕ)$, and analyze their evolutionary behavior across cosmic time. The study also evaluates the model's physical…
In this paper, we first obtain the energy density by the approach of the new agegraphic dark energy model, and then the $f(T,B)$ gravity model is studied as an alternative to the dark energy in a viscous fluid by flat-FRW background, in which $T$ and $B$ are torsion scalar and boundary term. The Friedmann equations will obtain in the framework of modified teleparallel gravity by tetrad components. We consider that the universe dominates with components such as matter and dark energy by an interacting model. The Hubble parameter is parameterized by the power-law for the scale factor, and then w…
We study the evolution of the universe in the presence of inflaton, matter, radiation, and holographic dark energy. The time evolution of the scale factor is obtained by solving the Friedmann equation of the universe with a good approximation. We present two independent ways which determine the value of the dark energy constant $d\sim 1$ from the observational data. The two ways are measuring the deceleration parameter and measuring a universal constant depending only on $d$. The universal constant is given by a dimensionless combination of three scale factors at the equipartition times of rad…
Gravitational particle production has been investigated by using Einstein's gravitational field equations in the presence of a cosmological constant. To study the mechanism of particle creation, the Universe has been considered as a thermodynamics system and non-equilibrium thermodynamics has been employed. In order to estimate the cosmological parameters with observational data, including SNe Ia, BAO, Planck 2015 and HST, we have chosen a phenomenological approach for the rate of particle creation. A non-zero particle production rate was obtained implying that the possibility of the particle …
Observational constraints on the modified cosmology inspired by string T-duality
Universidad de Lleida（莱里达大学）；Durban University of Technology（德班理工大学）；National Institute for Theoretical and Computational Sciences (NITheCS)（南非理论与计算科学国家研究所）；Universidad Catòlica del Norte（北天主教大学）；Shiraz University（设拉子大学）
