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We discuss a cosmology in which cold dark-matter particles decay into relativistic particles. We argue that such decays could lead naturally to a bulk viscosity in the cosmic fluid. For decay lifetimes comparable to the present hubble age,…

Astrophysics · Physics 2008-11-26 James R. Wilson , Grant J. Mathews , George M. Fuller

We study the late acceleration of the universe by incorporating bulk viscous matter with the running vacuum. The vacuum energy density varies as the squares of the Hubble parameter ($\rho_{\Lambda}\propto H^2$), and the coefficient of bulk…

General Relativity and Quantum Cosmology · Physics 2022-04-27 Sarath N , Jerin Mohan N D , Titus K Mathew

Conformally flat tilted Bianchi type V cosmological models in presence of a bulk viscous fluid and heat flow are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. The cosmological constant is…

General Relativity and Quantum Cosmology · Physics 2008-07-30 Anirudh Pradhan , S. K. Srivastav

We study a full causal bulk viscous cosmological model with flat FRW symmetries and where the ``constants'' $G,c$ and $\Lambda $ vary. We take into account the possible effects of a $c-$variable into the curvature tensor in order to outline…

General Relativity and Quantum Cosmology · Physics 2016-08-16 J. A. Belinchón

Based on the assumption that the dark energy possessing bulk viscosity is homogenously and isotropically permeated in the universe, we propose three new viscous dark energy (VDE) models to characterize the accelerating universe. By…

Cosmology and Nongalactic Astrophysics · Physics 2021-03-30 Deng Wang , Yang-Jie Yan , Xin-He Meng

We investigate the cosmological viability of symmetric teleparallel gravity, specifically the $f(Q)$ gravity model with a power-law form $f(Q) = \alpha Q^n$, in combination with two widely used dark energy parameterizations: Chevallier…

General Relativity and Quantum Cosmology · Physics 2025-07-09 Rajdeep Mazumdar , Mrinnoy M. Gohain , Kalyan Bhuyan

In this study, we investigate the cosmological history within the framework of modified $f(Q)$ gravity, which proposes an alternative theory of gravity where the gravitational force is described by a non-metricity scalar. By employing a…

General Relativity and Quantum Cosmology · Physics 2023-08-30 N. Myrzakulov , M. Koussour , A. Mussatayeva

In this paper, we explore the model of $f(Q,T)$ gravity, an extension of symmetric teleparallel gravity where the nonmetricity scalar $Q$ is non-minimally coupled to the trace of the energy-momentum tensor $T$. To ensure general covariance…

General Relativity and Quantum Cosmology · Physics 2025-09-09 Rahul Bhagat , Santosh V. Lohakare , B. Mishra

A generally parameterized equation of state (EOS) is investigated in the cosmological evolution with bulk viscosity media modelled as dark fluid, which can be regarded as a unification of dark energy and dark matter. Compared with the case…

Astrophysics · Physics 2009-11-13 J. Ren , Xin He Meng

The viscous Cardassian cosmology is discussed, assuming that there is a bulk viscosity in the cosmic fluid. The dynamical analysis indicates that there exists a singular curve in the phase diagram of viscous Cardassian model. In the viscous…

General Relativity and Quantum Cosmology · Physics 2014-11-18 Chang-Bo Sun , Jia-Ling Wang , Xin-Zhou Li

In this paper, we investigate Bianchi type$-V$ cosmological models with bulk viscous fluid and time varying cosmological $\Lambda$ and Newtonian $G$ parameters. The Einstein's field equations have been transformed into a coupling…

A model with flat FRW symmetries and G and Lambda variable,is considered in such a way that the momentum-energy tensor that describes the model is characterized by a bulk viscosity parameter. In this paper it is showed how to apply the…

General Physics · Physics 2007-05-23 J. A. Belinchon

We consider the evolution of a flat Friedmann-Robertson-Walker Universe, filled with a causal bulk viscous cosmological fluid, in the presence of variable gravitational and cosmological constants. The basic equation for the Hubble…

General Relativity and Quantum Cosmology · Physics 2008-11-26 M. K. Mak , J. A. Belinchon , T. Harko

Bulk viscosity in cold dark matter is an appealing feature that introduces distinctive phenomenological effects in the cosmological setting as compared to the $\Lambda$CDM model. Under this view, we propose a general parametrization of the…

General Relativity and Quantum Cosmology · Physics 2023-08-24 Gabriel Gómez , Guillermo Palma , Ángel Rincón , Norman Cruz , Esteban González

We probe into universes filled with Quark Gluon Plasma with non-zero viscosities. In particular, we study the evolution of a universe with non-zero shear viscosity motivated by the theoretical result of a non-vanishing shear viscosity in…

General Relativity and Quantum Cosmology · Physics 2019-10-03 Sergio Bravo Medina , Marek Nowakowski , Davide Batic

Spatially homogeneous and anisotropic Bianchi type V space-time with bulk viscous fluid source and time varying gravitational constant $G$ and cosmological term $\Lambda$ are considered. Coefficient of bulk viscosity $\zeta$ is assumed as a…

General Relativity and Quantum Cosmology · Physics 2012-05-25 Prashant S. Baghel , J. P. Singh

This paper examines the late-time accelerating Universe and the formation of large-scale structures within the modified symmetric teleparallel gravity framework, specifically using the $f(Q)$-gravity model, in light of recent cosmological…

General Relativity and Quantum Cosmology · Physics 2024-12-31 Shambel Sahlu , Amare Abebe

Despite the significant accomplishments of general relativity, numerous unresolved issues persist in our understanding of the cosmos. One of the most perplexing challenges is the ongoing accelerated expansion of the Universe, which…

Cosmology and Nongalactic Astrophysics · Physics 2023-11-22 M. Koussour , N. Myrzakulov , Alnadhief H. A. Alfedeel , Amare Abebe

Within the limits of the present cosmological observations in f(R,T) gravity theory, we have analyzed a spherically symmetric space-time in 5D setting. The field equations have been carefully studied considering reasonable cosmological…

General Relativity and Quantum Cosmology · Physics 2020-10-28 Pheiroijam Suranjoy Singh , Kangujam Priyokumar Singh

In this study, we examined the late-time cosmic expansion of the universe within the framework of $f(Q, L_m)$ gravity, where $Q$ denotes the non-metricity and $L_{m}$ represents the matter Lagrangian. We analyzed a linear $f(Q, L_m)$ model…

Cosmology and Nongalactic Astrophysics · Physics 2024-08-15 Yerlan Myrzakulov , O. Donmez , M. Koussour , D. Alizhanov , S. Bekchanov , J. Rayimbaev