Browsing by Author "Patel, L.K."

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A class of cylindrically symmetric models in string cosmology
(2015-02-09) Tikekar, R.; Patel, L.K.; Dadhich, Naresh
A new class of physically relevant explicit solutions for string cosmological models endowed with cylindrical symmetry on the background of singularity free cosmological space times have been obtained and their physical and the kinematical features are discussed. The matter free limits of this class of solutions are observed to be the singularity free vacuum solutions of Patel and Dadhich.
Cylindrical universes with heat and null radiation flow
(2014-11-25) Patel, L.K.; Dadhich, Naresh
In paper-I(Patel and Dadhich ,1992) we have discussed cylindrically symmetric viscous fluid models with the Kasnerian time evolution. In this paper we incorporate heat flow and null radiation flow with the perfect fluid. Here again, in the case of heat flow the Kasner spacetime is the matter-free limit of the model. We establish a general result that a static perfect fluid distribution will on Kasnerization (introduce t4/3, t4/3, and t−2/3 in the coefficients of dr2, dΦ2, and dz2) yield a time-dependent distribution with the same equation of state and with or without heat flow.
Cylindrically symmetric cosmological models in the Kaluza-Klein space time
(2015-01-27) Patel, L.K.; Dadhich, Naresh
We consider a non-diagonal cylindrically symmetric metric in the Kaluza-Klein spacetime. We obtain a number of homogeneous and inhomogeneous perfect fluid cosmological models, which include the 5-dimensional analogue of the recently found 4-dimensional non-singular stiff fluid model. Amongst the homogeneous models, which are all as expected big-bang singular, there is the 5-dimensional version of the Friedman-Robertson-Walker flat model.
Cylindrically symmetric viscous universes
(2014-11-26) Patel, L.K.; Dadhich, Naresh
We have considered here cylindrically symmetric cosmological models with viscous fluid having the Kasnerian time evolution. It turns out that the ‘‘no‐matter’’ limit of our geodetic viscous universes, which can as well be looked upon as string dust universes, is the non-flat empty Kasner spacetime. We thus propose that the universe may be born with the Kasner geometry at t = 0 with matter in the form of viscous fluid, then it may follow the path: geodetic to non-geodetic and finally to the radiation phase when viscosity is fully worn out. We have solutions to describe each phase separately.
Domain walls in kaluza-klein spacetime
(2015-03-01) Patel, L.K.; Dadhich, Naresh; Tikekar, R.
Three families of exact solutions of Einstein field equations are found. Each family contains three parameters. Two of these families represent thick domain walls in a five dimensional Kaluza-Klein spacetime.The dynamical behaviour of our models is briefly discussed. The spacetime in all the cases is found to be reflection symmetric with respect to the wall.
A duality relation for fluid spacetime
(2015-03-11) Dadhich, Naresh; Patel, L.K.; Tikekar, R.
Exact solutions for null fluid collapse in higher dimensions
(2015-03-01) Patel, L.K.; Dadhich, Naresh
A large family of inhomogeneous non-static spherically symmetric solutions of the Einstein equation for null fluid in higher dimensions has been obtained. It encompasses higher dimensional versions of many previously known solutions such as Vaidya, charged Vaidya and Husain solutions and also some new solutions representing global monopole or string dust. It turns out that physical properties of the solutions carry over to higher dimensions.
Global monopole as dual-vacuum solution in kaluza-klein spacetime
(2015-03-01) Dadhich, Naresh; Patel, L.K.; Tikekar, R.
By application of the duality transformation, which implies interchange of active and passive electric parts of the Riemann curvature (equivalent to interchange of Ricci and Einstein tensors) it is shown that the global monopole solution in the Kaluza-Klein spacetime is dual to the corresponding vacuum solution. Further we also obtain solution dual to flat space which would in general describe a massive global monopole in 4-dimensional Euclidean space and would have massless limit analogus to the 4-dimensional dual-flat solution.
Gravoelectric-dual of the kerr solution
(2015-03-01) Dadhich, Naresh; Patel, L.K.
By decomposing the Riemann curvature into electric and magnetic parts, we define the gravoelectric duality transformation by interchange of active and passive electric parts which amounts to interchange of the Ricci and Einstein tensors. It turns out that the vacuum equation is duality-invariant. We obtain solutions dual to the Kerr solution by writing an effective vacuum equation in such a way that it still admits the Kerr solution but is not duality invariant. The dual equation is then solved to obtain the dual-Kerr solution which can be interpreted as the Kerr black hole sitting in a string dust universe.
Higher dimensional analogue of McVittie solution
(2015-03-01) Patel, L.K.; Tikekar, R.; Dadhich, Naresh
Inhomogeneous cosmological models with heat flux
(2015-02-07) Patel, L.K.; Tikekar, R.; Dadhich, Naresh
We present a general class of inhomogeneous cosmological models filled with non-thermalized perfect fluid by assuming that the background spacetime admits two space-like commuting Killing vectors and has separable metric coefficients. The singularity structure of these models depends on the choice of the parameters and the metric functions, A number of previously known perfect fluid models follow as particular cases of this general class. Physical and geometrical features of these models are studied and the general expression for temperature distribution is given
On singularity free cosmological model
(2015-01-13) Dadhich, Naresh; Tikekar, R.; Patel, L.K.
The role of shear in expanding cylindrical perfect fluid models
(2015-01-27) Dadhich, Naresh; Patel, L.K.
For orthogonal cylindrically symmetric expanding perfect fluid spacetime we prove that vanishing of shear implies vanishing of acceleration which further renders spacetime homogeneous. That means inhomogeneous spacetimes must always be shearing and anisotropic. Non-singular spacetimes will thus be both inhomogeneous and anisotropic.
A simple shear-free-non-singular spherical model with heat flux
(2015-03-01) Dadhich, Naresh; Patel, L.K.
We obtain an exact simple solution of the Einstein equation describing a spherically symmetric cosmological model without the bigbang or any other kind of singularity. The matter content of the model is shear free isotropic fluid with radial heat flux and it satisfies the weak and strong energy conditions. It is pressure gradient combined with heat flux that prevents occurrence of singularity. So far all known non-singular models have non-zero shear. This is the first shear free non-singular model, which is also spherically symmetric.
Singularity free inhomogeneous viscous fluid cosmological models
(2014-11-23) Patel, L.K.; Dadhich, Naresh
We obtain two new classes of singularity free inhomogeneous viscous fluid cosmological solutions, which reduce to the Senovilla [1] class when viscosity is switched off. It is interesting to note that inclusion of viscosity does not disturb the singularity free character and general behavior of the models remains qualitatively same.
String-dust in Einstein and godel universes
(2015-01-27) Dadhich, Naresh; Patel, L.K.
We consider the mixture of perfect fluid and string-dust and obtain string-dust generalization of the Einstein and godel universes.