Research Papers (TP)

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    Bounds on vacuum energy density in a general cosmological scenario
    (Elsevier Science Publishers, 1987-02-09) Joshi, P. S.; Padmanabhan, T.; Chitre, S. M.
    General limits on the cosmological constant (or equivalently the vacuum energy density) are derived for an inflationary universe. This is accomplished under the general assumption of global hyperbolicity and without the use of any special properties like spherical symmetry or homogeneity ofthe underlying spacetime. Aclear upper limit of 1/3 is obtained for the vacuum energy density parameterQ~,while the lower limit is found to depend on the age of the oldest object in the universe.
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    Is gravitational lensing a local phenomenon caused by Pop - III objects?
    (Gordon and Breach Science Publishers, 1986-01-31) Padmanabhan, T.; Chitre, S. M.
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    Temperature fluctuations of cosmic microwave background induced by gravitational lensing
    (Elsevier Science Publishers, 1986-08-25) Chitre, S. M.; Narlikar, J. V.; Padmanabhan, T.
    Adopting the accepted interpretation of the cosmic microwave background (CMBR) as a relic of the early hot universe we show that any angular intensity variations existing in the background at the "last scattering surface" at the redshift of ~10³ will induce bright fluctuations through gravitational lensing by intervening masses. The resulting temperature variations ΔT are estimated for gravitating masses like distant galaxies (z ~1) and local dark objects (e.g. population III stars) in our own Galaxy. It is found that the value of ΔT/T produced by the above mechanisms further constrains the theories of galaxy formation. The calculation also limits the amount of matter present in the form of population III objects in the galaxy.
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    Viscous universes
    (Elsevier Science Publishers, 1987-03-23) Padmanabhan, T.; Chitre, S. M.
    The effect of bulk viscosity on the evolution of the universe at large is investigated. It is demonstrated that bulk viscosity can lead to inflation-like solutions.