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      Supergravity, Dark Energy and the Fate of the Universe

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          Abstract

          We propose a description of dark energy and acceleration of the universe in extended supergravities with de Sitter (dS) solutions. Some of them are related to M-theory with non-compact internal spaces. Masses of ultra-light scalars in these models are quantized in units of the Hubble constant: m^2 = n H^2. If dS solution corresponds to a minimum of the effective potential, the universe eventually becomes dS space. If dS solution corresponds to a maximum or a saddle point, which is the case in all known models based on N=8 supergravity, the flat universe eventually stops accelerating and collapses to a singularity. We show that in these models, as well as in the simplest models of dark energy based on N=1 supergravity, the typical time remaining before the global collapse is comparable to the present age of the universe, t = O(10^{10}) years. We discuss the possibility of distinguishing between various models and finding our destiny using cosmological observations.

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          SUPERGRAVITY DESCRIPTION OF FIELD THEORIES ON CURVED MANIFOLDS AND A NO GO THEOREM

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            A Dynamical Solution to the Problem of a Small Cosmological Constant and Late-time Cosmic Acceleration

            Increasing evidence suggests that most of the energy density of the universe consists of a dark energy component with negative pressure, a ``cosmological constant" that causes the cosmic expansion to accelerate. In this paper, we address the puzzle of why this component comes to dominate the universe only recently rather than at some much earlier epoch. We present a class of theories based on an evolving scalar field where the explanation is based entirely on internal dynamical properties of the solutions. In the theories we consider, the dynamics causes the scalar field to lock automatically into a negative pressure state at the onset of matter-domination such that the present epoch is the earliest possible time, consistent with nucleosynthesis restrictions, when it can start to dominate.
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              The Case for a Positive Cosmological Lambda-term

              Recent observations of Type 1a supernovae indicating an accelerating universe have once more drawn attention to the possible existence, at the present epoch, of a small positive Lambda-term (cosmological constant). In this paper we review both observational and theoretical aspects of a small cosmological Lambda-term. We discuss the current observational situation focusing on cosmological tests of Lambda 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 Lambda: the generation of Lambda in models with spontaneous symmetry breaking and through quantum vacuum polarization effects -- mechanisms which are known to give rise to alarge value of Lambda hence leading to the `cosmological constant problem'. More recent attempts to generate a small cosmological constant at the present epoch using either field theoretic techniques, or by modeling a dynamical Lambda-term by scalar fields are also extensively discussed. Anthropic arguments favouring a small cosmological constant are briefly reviewed. A comprehensive bibliography of recent work on Lambda is provided.
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                Author and article information

                Journal
                10.1103/PhysRevD.66.123503
                hep-th/0208156

                General relativity & Quantum cosmology,General astrophysics,High energy & Particle physics

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