Professor T. Padmanabhan

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End date: 1989Subject: search.filters.subject.Cosmology

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    Horizon problem and inflation
    (Indian Academy of Sciences, 1987-06-24) Padmanabhan, T.; Seshadri, T. R.
    We show that, the part of the universe that is observable today (in principle), could not have evolved out of a domain which was causally connected in the past. This and other issues related to horizon problem in inflationary models are discussed.
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    Dynamical scenarios with unstable neutrinos
    (American Astronomical Society, 1987-04-15) Padmanabhan, T.; Vasanthi, M. M.
    We describe a cosmological scenario with an unstable warm dark matter candidate (a heavy neutrino νH with mass of ~120 eV) which decays into a “hot” particle (a light nuetrino νL with mass of ~6 eV) and a relativistic boson. Theoretical and observational constraints on such a model are discussed. We note that (1) decay of νH disrupts the condensates made of primordial νL, lowering their mass to acceptable values of ~1012 M⊙. (2) The relativistic boson can contribute nearly 0.25 to the total density in a “recent” decay. The model predicts two prominent scales in dark matter distribution: (i) a mass of about ~4 × 1012M⊙ around the galaxies, distributed over about ~200 kpc, and (ii)a smoother density of ~10-27 g cm-3 distributed over ~1 Mpc. We argued that the model agrees with observations at all scales.
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    Gaussian states in the De-Sitter spacetime and the evolution of semiclassical density perturbations: 1. Homogeneous mode
    (Indian Academy of Sciences, 1989-08-08) Seshadri, T. R.; Padmanabhan, T.
    The evolution of Gaussian quantum states in the de Sitter phase of the early universe is investigated. The potential is approximated by that of an inverted oscillator. We study the origin and magnitude of the density perturbations with special emphasis on the nature of the semiclassical limits.
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    Quantum fluctuations and the non-avoidance of singularities in bianchi type I cosmologies
    (Springer, 1980-04-28) Padmanabhan, T.
    An effective metric is defined and used for analyzing the quantum fluctuations in a classical geometry. Early work showing that quantum conformal fluctuations avoid the classical singularity in the case of spherically symmetric collapse is briefly reviewed it is shown that this result does not extend to anisotropic Bianchi type I cosmology. Here the dispersion in the fluctuations increase to slowly to quench the classical singularity. The singularity persists in the space-time describe by the effective metric.
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    Quantum cosmology as a cure for three ailments of classical cosmology
    (Astronomical Society of India, 1983-08-12) Narlikar, J. V.; Padmanabhan, T.
    The standard big bang models of classical cosmology are known to possess three defects. The oldest known defect is spacetime singularity whose existence seems inevitable within the classical framework. The second defect is the existence of a particle horizon which severely limits communications across the distant parts of the universe whose observed homogeneity therefore becomes inexplicable. Recently a third defect has been highlighted, viz., the required fine tuning of the early universe close to the flat spatial model in order to account for the present range of its mean density. We show before that the injection of quantum ideas holds out hope of a cure for all the three ailments described above. Using a simple path integral formalism for quantum cosmology we present arguments which suggest that (i) it is extremely unlikely that the universe evolved to the present state from quantum states of singularity and particles horizon;(ii) of all the possible Robertson-Walker models that could evolve our of quantum fluctuations of the empty Minkowski universe the flat model is overwhelmingly probable.