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The linear cosmological perturbation theory of an almost homogeneous and isotropic perfect fluid universe is reconsidered and formally simplified by introducing new covariant and gauge-invariant variables with physical interpretations on…

General Relativity and Quantum Cosmology · Physics 2011-07-19 Winfried Zimdahl

Phantom cosmology allows to account for dynamics and matter content of the universe tracing back the evolution to the inflationary epoch, considering the transition to the non-phantom standard cosmology (radiation/matter dominated eras) and…

High Energy Physics - Theory · Physics 2008-11-26 S. Capozziello , S. Nojiri , S. D. Odintsov

We propose a new dark energy (DE) model from four parameter generalized entropy function of apparent horizon in a spatially flat universe. Such kind of generalized entropy is able to generalize all the known entropies proposed so far, for…

General Relativity and Quantum Cosmology · Physics 2025-07-22 Priyanka Adhikary , Sudipta Das , Sergei D. Odintsov , Tanmoy Paul

Here, we peruse cosmological usage of the most promising candidates of dark energy in the framework of f(R) theory. We reconstruct the different f(R) modified gravity models in the spatially flat FRW universe according to the ordinary and…

General Relativity and Quantum Cosmology · Physics 2011-07-18 K. Karami , M. S. Khaledian

The thermodynamical properties of dark energy are usually investigated with the equation of state $\omega =\omega_{0}+\omega_{1}z$. Recent observations show that our universe is accelerating, and the apparent horizon and the event horizon…

Astrophysics · Physics 2008-11-26 Yongping Zhang , Ze-Long Yi , Tong-Jie Zhang , Wenbiao Liu

Despite the success of Maxwell's electromagnetism in the description of the electromagnetic interactions on small scales, we know very little about the behaviour of electromagnetic fields on cosmological distances. Thus, it has been…

Cosmology and Nongalactic Astrophysics · Physics 2011-12-07 Jose Beltran Jimenez , Antonio L. Maroto

A generalized entropy arising in the context of superstatistics is obtained for an ideal gas. The curvature scalar associated to the thermodynamic space generated by this modified entropy is calculated using two formalisms of the geometric…

Statistical Mechanics · Physics 2018-04-18 J. L. López , O. Obregón , J. Torres-Arenas

It may be a common understanding at present that, once event horizons are in thermal equilibrium, the entropy-area law holds inevitably. However, no rigorous verification is given to such a very strong universality of the law in…

General Relativity and Quantum Cosmology · Physics 2011-09-06 Hiromi Saida

A possible solution to the dark energy problem is that Einstein's theory of general relativity is modified. A suite of models have been proposed that, in general, are unable to predict the correct amount of large scale structure in the…

Cosmology and Nongalactic Astrophysics · Physics 2010-05-28 Pedro G. Ferreira , Constantinos Skordis

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…

General Relativity and Quantum Cosmology · Physics 2016-11-02 Saugata Mitra , Subhajit Saha , Subenoy Chakraborty

The present work deals with universe bounded by the cosmological event horizon as a thermodynamical system which is irreversible in nature.Using non-equilibrium thermodynamical approach the entropy variation on the event horizon has been…

General Physics · Physics 2014-06-30 Subenoy Chakraborty , Atreyee Biswas

We study the semi-holographic idea in context of decaying dark components. The energy flow between dark energy and the compensating dark matter is thermodynamically generalized to involve a particle number variable dark component with…

Cosmology and Nongalactic Astrophysics · Physics 2015-06-12 Hui Li , Hongsheng Zhang , Yi Zhang

In this paper, we discuss the thermodynamical analysis for gravitationally induced particle creation scenario in the framework of DGP braneworld model. For this purpose, we consider apparent horizon as the boundary of the universe. We take…

General Physics · Physics 2018-03-14 Abdul Jawad , Shamaila Rani , Salman Rafique

It is shown that the first law of thermodynamics and the holographic principle applied to an arbitrary large cosmic causal horizon naturally demand the zero cosmological constant and non-zero dynamical dark energy in the form of the…

High Energy Physics - Theory · Physics 2015-03-13 Jae-Weon Lee

We suggest the modified gravity where some arbitrary function of Gauss-Bonnet (GB) term is added to Einstein action as gravitational dark energy. It is shown that such theory may pass solar system tests. It is demonstrated that modified GB…

High Energy Physics - Theory · Physics 2010-04-06 Shin'ichi Nojiri , Sergei D. Odintsov

A classical and quantum mechanical generalized second law of thermodynamics in cosmology implies constraints on the effective equation of state of the universe in the form of energy conditions, obeyed by many known cosmological solutions,…

General Relativity and Quantum Cosmology · Physics 2009-10-31 Ram Brustein

For several independent reasons, the idea that notorious sources of entropy could exist in the Universe has been recently revived. Taking advantage of a new framework accounting for non-equilibrium processes in cosmology, we explicitly…

General Relativity and Quantum Cosmology · Physics 2025-05-27 Jamy-Jayme Thézier , Aurélien Barrau , Killian Martineau

The cosmological Friedmann equation sourced by the trace anomaly of a conformal field theory that is dual to the five-dimensional Schwarzschild-AdS geometry can be derived from the first law of thermodynamics if the apparent horizon of the…

High Energy Physics - Theory · Physics 2013-11-20 James E. Lidsey

In this work we explore some cosmological properties coming from the particle and future horizons when are considered as candidates to model the dark energy sector within a holographic context in a flat Friedmann-Lemaitre-Robertson-Walker…

General Relativity and Quantum Cosmology · Physics 2020-04-29 Miguel Cruz , Samuel Lepe

The dark energy universe equation of state (EOS) with inhomogeneous,Hubble parameter dependent term is considered. The motivation to introduce such a term comes from time-dependent viscosity considerations and modifications of general…

High Energy Physics - Theory · Physics 2008-11-26 Shin'ichi Nojiri , Sergei D. Odintsov