251 research outputs found

    A model of nonsingular universe

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    In the background of Friedmann-Robertson-Walker Universe, there exists Hawking radiation which comes from the cosmic apparent horizon due to quantum effect. Although the Hawking radiation on the late time evolution of the universe could be safely neglected, it plays an important role in the very early stage of the universe. In view of this point, we identify the temperature in the scalar field potential with the Hawking temperature of cosmic apparent horizon. Then we find a nonsingular universe sourced by the temperature-dependant scalar field. We find that the universe could be created from a de Sitter phase which has the Planck energy density. Thus the Big-Bang singularity is avoided.Comment: 6 pages, 3 figures. To appear in Entrop

    A Static Spherically Symmetric Solution of the Einstein-aether Theory

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    By using of the Euler-Lagrange equations, we find a static spherically symmetric solution in the Einstein-aether theory with the coupling constants restricted. The solution is similar to the Reissner-Nordstrom solution in that it has an inner Cauchy horizon and an outer black hole event horizon. But a remarkable difference from the Reissner-Nordstrom solution is that it is not asymptotically flat but approaches a two dimensional sphere. The resulting electric potential is regular in the whole spacetime except for the curvature singularity. On the other hand, the magnetic potential is divergent on both Cauchy horizon and the outer event horizon.Comment: 12 pages, 8 figures. To appear in PR

    Cosmic evolution of scalar fields with multiple vacua: generalized DBI and quintessence

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    We find a method to rewrite the equations of motion of scalar fields, generalized DBI field and quintessence, in the autonomous form for\emph{arbitrary} scalar potentials. With the aid of this method, we explore the cosmic evolution of generalized DBI field and quintessence with the potential of multiple vacua. Then we find that the scalars are always frozen in the false or true vacuum in the end. Compared to the evolution of quintessence, the generalized DBI field has more times of oscillations around the vacuum of the potential. The reason for this point is that, with the increasing of speed ϕ˙\dot{\phi}, the friction term of generalized DBI field is greatly decreased. Thus the generalized DBI field acquires more times of oscillations.Comment: 8 pages, 9 figures, accepted by IJTP. A number of typos correcte