18,432 research outputs found

    Variable Speed of Light Cosmology and Bimetric Gravity: An Alternative to Standard Inflation

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    A scalar-tensor bimetric gravity model of early universe cosmology is reviewed. The metric frame with a variable speed of light (VSL) and a constant speed of gravitational waves is used to describe a Friedmann-Robertson-Walker universe. The Friedmann equations are solved for a radiation dominated equation of state and the power spectrum is predicted to be scale invariant with a scalar mode spectral index ns=0.97n_s=0.97. The scalar modes are born in a ground state superhorizon and the fluctuation modes are causally connected by the VSL mechanism. The cosmological constant is equated to zero and there is no significant dependence on the scalar field potential energy. A possible way of distinguishing the metric gravity model from standard inflationary models is discussed.Comment: 10 pages. Latex file. No figures. Talk given at the Coral Gables Conference on High Energy Physics and Cosmology, Fort Lauderdale, Florida, December 17-21, 2003. Typos corrected. Reference adde

    Massive NGT and Spherically Symmetric Systems

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    The arguments leading to the introduction of the massive Nonsymmetric Gravitational action are reviewed \cite{Moffat:1994,Moffat:1995b}, leading to an action that gives asymptotically well-behaved perturbations on GR backgrounds. Through the analysis of spherically symmetric perturbations about GR (Schwarzschild) and NGT (Wyman-type) static backgrounds, it is shown that spherically symmetric systems are not guaranteed to be static, and hence Birkhoff's theorem is not valid in NGT. This implies that in general one must consider time dependent exteriors when looking at spherically symmetric systems in NGT. For the surviving monopole mode considered here there is no energy flux as it is short ranged by construction. Further work on the spherically symmetric case will be motivated through a discussion of the possibility that there remain additional modes that do not show up in weak field situations, but nonetheless exist in the full theory and may again result in bad global asymptotics. A presentation of the action and field equations in a general frame is given in the course of the paper, providing an alternative approach to dealing with the algebraic complications inherent in NGT, as well as offering a more general framework for discussing the physics of the antisymmetric sector.Comment: `Final' version (minor changes have been made to the original), to be published in J. Math. Phys. Typset using ReVTeX and amssymbols. 29 page

    Issues in Quantum-Geometric Propagation

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    A discussion of relativistic quantum-geometric mechanics on phase space and its generalisation to the propagation of free, massive, quantum-geometric scalar fields on curved spacetimes is given. It is shown that in an arbitrary coordinate system and frame of reference in a flat spacetime, the resulting propagator is necessarily the same as derived in the standard Minkowski coordinates up to a Lorentz boost acting on the momentum content of the field, which is therefore seen to play the role of Bogolubov transformations in this formalism. These results are explicitly demonstrated in the context of a Milne universe.Comment: 19 pages; requires amsart, amssymb, amsmat

    Interface-induced magnetism in perovskite quantum wells

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    We investigate the angular dependence of the magnetoresistance of thin (< 1 nm), metallic SrTiO3 quantum wells epitaxially embedded in insulating, ferrimagnetic GdTiO3 and insulating, antiferromagnetic SmTiO3, respectively. The SrTiO3 quantum wells contain a high density of mobile electrons (~7x10^14 cm^-2). We show that the longitudinal and transverse magnetoresistance in the structures with GdTiO3 are consistent with anisotropic magnetoresistance, and thus indicative of induced ferromagnetism in the SrTiO3, rather than a nonequilibrium proximity effect. Comparison with the structures with antiferromagnetic SmTiO3 shows that the properties of thin SrTiO3 quantum wells can be tuned to obtain magnetic states that do not exist in the bulk material.Comment: Accepted for publication as a Rapid Communication in Physical Review
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