1999 (IPP)

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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.
Oscillating non-singular relativistic spherical model
(2015-03-01) Dadhich, Naresh; Raychaudhuri, A.K.
A particular choice of the time function in the recently presented spherical solution by Dadhich [1] leads to a singularity free cosmological model which oscillates between two regular states. The energy-stress tensor involves anisotropic pressure and a heat flux term but is consistent with the usual energy conditions (strong, weak and dominant). By choosing the parameters suitably one can make the model consistent with observational data. An interesting feature of the model is that it involves blue shifts as in the quasi steady state model [2] but without violating general relativity.