ar X iv : g r - qc / 9 31 20 25 v 1 1 5 D ec 1 99 3 Curvature and Flatness in a Brans - Dicke Universe
نویسنده
چکیده
The evolution of a universe with Brans-Dicke gravity and nonzero curvature is investigated here. We present the equations of motion and their solutions during the radiation dominated era. In a Friedman-Robertson-Walker cosmology we show explicitly that the three possible values of curvature κ = +1, 0,−1 divide the evolution of the Brans-Dicke universe into dynamically distinct classes just as for the standard model. Subsequently we discuss the flatness problem which exists in Brans-Dicke gravity as it does in the standard model. In addition, we demonstrate a flatness problem in MAD Brans-Dicke gravity. In general, in any model that addresses the horizon problem, including inflation, there are two components to the flatness issue: i) at the Planck epoch curvature gains importance, and ii) during accelerated expansion curvature becomes less important and the universe flattens. In many cases the universe must be very flat at the Planck scale in order for the accelerated epoch to be reached, thus there can be a residual flatness problem. to be published in Nuclear Physics B, submitted August 30, 1993
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ar X iv : g r - qc / 9 50 20 02 v 1 1 F eb 1 99 5 YITP / U - 95 - 2 Density fluctuations in Brans - Dicke inflation ∗
Spectrum of density perturbations in the Universe generated from quantumgravitational fluctuations in slow-roll-over inflationary scenarios with the Brans-Dicke gravity is calculated. It is shown that after inflation the isocurvature mode of perturbations may be neglected as compared to the adiabatic mode, and that an amplitude of the latter mode is not significantly different from that in the ...
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