2000 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/629
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Item New cosmological model of quintessence and dark matter(2000-01-14) Sahni, Varun; Wang, LiminWe propose a new class of quintessence models in which late times oscillations of a scalar field give rise to an effective equation of state which can be negative and hence drive the observed acceleration of the universe. Our ansatz provides a unified picture of quintessence and a new form of dark matter we call Frustrated Cold Dark Matter (FCDM). FCDM inhibits gravitational clustering on small scales and could provide a natural resolution to the core density problem for disc galaxy halos. Since the quintessence field rolls towards a small value, constraints on slow-roll quintessence models are safely circumvented in our model.Item Living with Lambda(2000-10-24) Sahni, VarunThis talk presents a brief overview of recent results pertaining to the cosmological con- stant ‘ ’. I summarize the observational situation focussing on observations of high redshift Type Ia supernovae which suggest > 0. Observations of small angular anisotropies in the cosmic mi- crowave background complement Type Ia supernovae observations and both CMB and Sn can be combined to place strong constraints on the value of . The presence of a small -term increases the age of the universe and slows down the formation of large scale structure. I also review recent the- oretical attempts to generate a small -term at the current epoch and a model independent approach for determining the cosmic equation of state.Item Case for a Positive Cosmological Lambda-term(2000-04-25) Sahni, Varun; Starobinsky, A. A.Recent observations of Type 1a supernovae indicating an accelerat- ing universe have once more drawn attention to the possible existence, at the present epoch, of a small positive Λ-term (cosmological constant). In this paper we review both observational and theoretical aspects of a small cosmological Λ-term. We discuss the current observational situation focusing on cosmolog- ical tests of Λ including the age of the universe, high redshift supernovae, gravitational lensing, galaxy clustering and the cosmic microwave background. We also review the theoretical debate surrounding Λ: the generation of Λ in models with spontaneous symmetry breaking and through quantum vacuum polarization effects – mechanisms which are known to give rise to a large value of Λ hence leading to the ‘cosmological constant problem’. More recent at- tempts to generate a small cosmological constant at the present epoch using either field theoretic techniques, or by modeling a dynamical Λ-term by scalar fields are also extensively discussed. Anthropic arguments favouring a small Λ-term are briefly reviewed. A comprehensive bibliography of recent work on Λ is provided.