Browsing by Author "Pradhan, Anirudh"

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Bulk viscous solutions to the field equations and the deceleration parameter - revisited
(2011-07-06) Pradhan, Anirudh; Lotemshi, I.
We utilise a form for the Hubble parameter to generate a number of solutions to the Einstein ﬁeld equations with variable cosmological constant and variable gravitational constant in the presence of a bulk viscous ﬂuid. The Hubble law utilised yields a constant value for the deceleration parameter. A new class of solutions is presented in the Robertson-Walker spacetimes. The coefﬁcient of bulk vis- cosity is assumed to be a power function of the mass density. For a class of solutions, the deceleration parameter is negative which is consistent with the supernovae Ia observations.
Emergence and Expansion of Cosmic Space in BIonic system
(IUCAA, 2015-02) Sepehri, A.; Rahaman, Farook; Pradhan, Anirudh
Kaluza-Klein Type Robertson Walker Cosmological Model With Dynamical Cosmological Term Lambda
(2005-12-01) Pradhan, Anirudh; Khadekar, G. S.; Patki, Vrishali
In this paper we have analyzed the Kaluza-Klein type RobertsonWalker (RW) cosmological models by considering three diﬀerent forms of variable Λ: Λ ∼˙ a a 2 , Λ ∼ ¨ a a and Λ ∼ ρ. It is found that, the connecting free parameters of the models with cosmic matter and vacuum energy density parameters are equivalent, in the context of higher dimensional space time. The expression for the look back time, luminosity distance and angular diameter distance are also derived. This work has thus generalized to higher dimensions the well-known results in four dimensional space time. It is found that there may be signiﬁcant diﬀerence in principle at least, from the analogous situation in four dimensional space time.
LRS Bianchi I cosmological universe models with varying cosmological term
(2000-02-25) Pradhan, Anirudh; Kumar, Ambarish
Einstein's eld equations with cosmological term varying with time are considered in the context of general homogeneous, anisotropic universes in a way which conserves the energy{momentum tensor of matter content. It is shown that the eld equations are solvable for any arbitrary cosmic scale functions. Some physical and geometrical features of the models are discussed.
A new class of LRS Bianchi Type –I cosmological models in lyra geometry
(2015-03-01) Pradhan, Anirudh; Vishwakarma, Anil Kumar
LRS Bianchi type-1 models have been studied in the cosmological theory based on Lyra's geometry. A new class of exact solutions has been obtained by considering a time dependent and constant displacement field for constant deceleration parameter models of the universe. The physical behaviour of the models is examined in vacuum and in the presence of perfect fluids.
Nonsingular spherical models with a variable cosmological term
(2011-07-06) Pradhan, Anirudh; Srivastava, Kashika; Lal, Amrit
Exact solutions of the Einstein’s ﬁeld equations describing a spheri- cally symmetric cosmological model without a big bang or any other kind of singularity recently obtained by Dadhich and Patel (2000) are revis- ited. The matter content of the model is a shear-free perfect ﬂuid with isotropic pressure and a radial heat ﬂux. Three diﬀerent exact solutions are obtained for both perfect ﬂuid and ﬂuid with bulk viscosity. It turns out that the cosmological rerm Λ(t) is a decreasing function of time, which is consistent with recent observations of type Ia supernovae.
Plane symmetric inhomogeneous bulk viscous domain wall in Lyra geometry
(2005-07-01) Pradhan, Anirudh; Rai, Vandana; Otarod, Saeed
Some bulk viscous general solutions are found for domain walls in Lyra geometry in the plane symmetric inhomogeneous spacetime. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying displacement ﬁeld β. The viscosity coeﬃcient of bulk viscous ﬂuid is assumed to be a power function of mass density. Some physical consequences of the models are also given. Finally, the geodesic equations and acceleration of the test particle are discussed.
Plane symmetric inhomogeneous cosmological models with a perfect fluid in general relativity
(2006-01-01) Pradhan, Anirudh; Pandey, Purnima; Singh, Sunil Kumar
In this paper we investigate a class of solutions of Einstein equations for the plane- symmetric perfect ﬂuid case with shear and vanishing acceleration. If these solutions have shear, they must necessarily be non-static. We examine the integrable cases of the ﬁeld equations systematically. Among the cases with shear we ﬁnd three classes of solutions.
Some Bianchi Type I Viscous fluid cosmological models with a variable cosmological constant
(2011-07-06) Pradhan, Anirudh; Pandey, Purnima
Some Bianchi type I viscous ﬂuid cosmological models with a variable cosmological constant are investigated in which the expansion is considered only in two direction i.e. one of the Hubble parameter (H1 = A4 A ) is zero. The viscosity coeﬃcient of bulk viscous ﬂuid is assumed to be a power function of mass density whereas the coeﬃcient of shear viscosity is considered as constant in ﬁrst case whereas in other case it is taken as proportional to scale of expansion in the model. The cosmological constant Λ is found to be positive and is a decreasing function of time which is supported by results from recent supernovae Ia observations. Some physical and geometric properties of the models are also discussed.
Universe with time dependent deceleration parameter and /\ term in general relativity
(2006-07-28) Pradhan, Anirudh; Otarod, Saeed
A new class of exact solutions of Einstein’s ﬁeld equations with perfect ﬂuid for an LRS Bianchi type-I spacetime is obtained by using a time dependent deceleration parameter. We have obtained a general solution of the ﬁeld equations from which three models of the universe are derived: exponential, polynomial and sinusoidal form respectively. The behaviour of these models of the universe are also discussed in the frame of reference of recent supernovae Ia observations.