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Full causal bulk viscous LRS Bianchi I with time varying constants  [PDF]
J. A. Belinchón
Physics , 2004, DOI: 10.1007/s10509-005-3424-4
Abstract: In this paper we study the evolution of a LRS Bianchi I Universe, filled with a bulk viscous cosmological fluid in the presence of time varying constants "but" taking into account the effects of a c-variable into the curvature tensor. We find that the only physical models are those which ``constants'' $G$ and $c$ are growing functions on time $t$, while the cosmological constant $\Lambda$ is a negative decreasing function. In such solutions the energy density obeys the ultrastiff matter equation of state i.e. $\omega=1$.
Bianchi Type V Universe with Bulk Viscous Matter and Time Varying Gravitational and Cosmological Constants  [PDF]
Prashant S. Baghel,J. P. Singh
Physics , 2012,
Abstract: 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 simple linear function of Hubble parameter $H$ (i.e. $\zeta=\zeta_0+\zeta_1 H$, where $\zeta_0$ and $\zeta_1$ are constants). The Einstein field equations are solved explicitly by using a law of variation for the Hubble parameter, which yields a constant value of deceleration parameter. Physical and kinematical parameters of the models are discussed. The models are found to be compatible with the results of astronomical observations.
Bianchi-Type VI0 Bulk Viscous Fluid Models with Variable Gravitational and Cosmological Constants  [PDF]
Manoj K. Verma, Shri Ram
Applied Mathematics (AM) , 2011, DOI: 10.4236/am.2011.23041
Abstract: This paper deals with Bianchi type VI0 anisotropic cosmological models filled with a bulk viscous cosmic fluid in the presence of time-varying gravitational and cosmological constant. Physically realistic solutions of Einstein's field equations are obtained by assuming the conditions 1) the expansion scalar is proportional to shear scalar 2) the coefficient of the bulk viscosity is a power function of the energy density and 3) the cosmic fluid obeys the barotropic equation of state. We observe that the corresponding models retain the well established features of the standard cosmology and in addition, are in accordance with recent type Ia supernovae observations. Physical behaviours of the cosmological models are also discussed.
Bianchi Type-V Bulk Viscous Barotropic Fluid Cosmological Model with Variable G and Λ
中国物理快报 , 2008,
Abstract: We investigate the Bianchi type-V bulk viscous barotropic fluid cosmological model with variable gravitational constant G and the cosmological constant Λ, assuming the condition on metric potential as A'/A=B'/B=C'/C=m/tn, where A, B, and C are functions of time t, while m and n are constants. To obtain the deterministic model, we also assume the relations P = p - 3ηH, p =γρ, η=η0ρs, where p is the isotropic pressure, η the bulk viscosity, 0≤γ≤1, H the Hubble constant, η0 and s are constants. Various physical aspects of the model are discussed. The case of n = 1 is also discussed to compare the results with the actual universe.
Tilted Bianchi Type V Bulk Viscous Cosmological Models in General Relativity  [PDF]
Anirudh Pradhan,Abha Rai
Physics , 2003, DOI: 10.1023/B:astr.0000032069.58003.b4
Abstract: 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. Some physical and geometric aspects of the models are also discussed.
Bianchi Type I Universes with Causal Bulk Viscous Cosmological Fluid  [PDF]
M. K. Mak,T. Harko
Physics , 2001, DOI: 10.1142/S0218271802001743
Abstract: We consider the dynamics of a causal bulk viscous cosmological fluid filled constantly decelerating Bianchi type I space-time. The matter component of the Universe is assumed to satisfy a linear barotropic equation of state and the state equation of the small temperature Boltzmann gas. The resulting cosmological models satisfy the condition of smallness of the viscous stress. The time evolution of the relaxation time, temperature, bulk viscosity coefficient and comoving entropy of the dissipative fluid is also obtained.
Bianchi Type III Bulk Viscous Barotropic Fluid Cosmological Models with Variable G and Λ
中国物理快报 , 2009,
Abstract: Bianchi type-III bulk viscous barotropic fluid cosmological model with variables G and Λ is investigated. To obtain the realistic model, we assume the conditions between the metric potentials A, B, C as ・A/A=・B/B=m1/tn and ・C/C=m2/tn, P=p-3ηH,η=η0 ρs, p =γρ, 0≤γ≤1, where p is isotropic pressure, η the coefficient of bulk viscosity, η0 and S the constants, H the Hubble constant, m1= 2m2 where m1>0, m2>0. The solutions obtained lead to inflationary phase and the results obtained match with the observations. The case n=1 for S=1 is also discussed, relating the results with the observations.
Bulk viscous FWR with time varying constants revisited  [PDF]
J. A. Belinchón
Physics , 2005,
Abstract: 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 the field equations. Using the Lie method we find the possible forms of the ``constants'' $G$ and $c$ that make integrable the field equations as well as the equation of state for the viscous parameter. It is found that $G,c$ and $\Lambda $ follow a power law solution verifying the relationship $G/c^{2}=\kappa .$ Once these possible forms have been obtained we calculate the thermodynamical quantities of the model in order to determine the possible values of the parameters that govern the quantities, finding that only a growing $G$ and $c$ are possible while $% \Lambda $ behaves as a negative decreasing function.
Tilted Bianchi Type V Bulk Viscous Cosmological Models with Varying $Λ$-Term  [PDF]
Anirudh Pradhan,S. K. Srivastav
Physics , 2004,
Abstract: 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 found to be a decreasing function of time, which is supported by results from recent type Ia supernovae observations. Some physical and geometric aspects of the models are also discussed.
Bulk Viscous Bianchi Type V Space-Time with Generalized Chaplygin Gas and with Dynamical G and Λ  [PDF]
Shubha S. Kotambkar, Gyan Prakash Singh, Rupali R. Kelkar
International Journal of Astronomy and Astrophysics (IJAA) , 2015, DOI: 10.4236/ijaa.2015.53025
Abstract: In this paper, bulk viscous Bianchi type V cosmological model with generalized Chaplygin gas, dynamical gravitational and cosmological constants has been investigated. We are assuming the condition on metric potential \"\". To obtain deterministic model, we have considered physically plausible relations like \"\", and the generalized Chaplygin gas is described by equation of state \"\". A new set of exact solutions of Einstein’s field equations has been obtained in Eckart theory, truncated theory and full causal theory. Physical behavior of the models has been discussed.
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