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arXiv 1102.2663gr-qc
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一般LTB尘埃模型中的反作用和有效加速度

Back-reaction and effective acceleration in generic LTB dust models

Roberto A Sussman

摘要:

我们提供了一个彻底的检查的条件存在的反反应和“有效”的加速度(在布歇特的平均形式主义的背景下)在经常通用的球对称Lemaitre-Tolman-Bondi(LTB)灰尘模型。通过考虑任意球形共动域,我们严格验证这些条件的履行表示在每个域的边界处进行评估的合适的标量变量。有效减速必然发生在所有的域中:(a)收敛到FLRW背景的模型的渐近径向范围,(b)非真空双曲模型的渐近时间范围,(c)LTB自相似解和(d)同时大爆炸附近。加速域被证明存在于下列情况下:(i)中央真空区,(ii)中央(非真空)密度空洞,(iii)收敛到FLRW背景的模型的中间径向范围,(iv)收敛到闵可夫斯基真空的模型的渐近径向范围和(v)附近和/或相交的非同时大爆炸域。所有这些场景都发生在双曲模型与负平均和局部空间曲率,虽然场景(iv)和(v)也可能在低密度区域的一类椭圆模型,其中局部空间曲率是负的,但其平均值是正的。发现有效减速参数的粗略数值估计在-0.003和-0.5之间。虽然在收敛到爱因斯坦德西特背景的模型中和在经历引力坍缩的区域中不能排除加速区域的存在,但这种情况的条件非常严格。所得结果可为更一般的非球模型中的反作用和平均效应提供重要的理论线索。

英文摘要:

We provide a thorough examination of the conditions for the existence of back-reaction and an "effective" acceleration (in the context of Buchert's averaging formalism) in regular generic spherically symmetric Lemaitre-Tolman-Bondi (LTB) dust models. By considering arbitrary spherical comoving domains, we verify rigorously the fulfillment of these conditions expressed in terms of suitable scalar variables that are evaluated at the boundary of every domain. Effective deceleration necessarily occurs in all domains in: (a) the asymptotic radial range of models converging to a FLRW background, (b) the asymptotic time range of non-vacuum hyperbolic models, (c) LTB self-similar solutions and (d) near a simultaneous big bang. Accelerating domains are proven to exist in the following scenarios: (i) central vacuum regions, (ii) central (non-vacuum) density voids, (iii) the intermediate radial range of models converging to a FLRW background, (iv) the asymptotic radial range of models converging to a Minkowski vacuum and (v) domains near and/or intersecting a non-simultaneous big bang. All these scenarios occur in hyperbolic models with negative averaged and local spatial curvature, though scenarios (iv) and (v) are also possible in low density regions of a class of elliptic models in which local spatial curvature is negative but its average is positive. Rough numerical estimates between -0.003 and -0.5 were found for the effective deceleration parameter. While the existence of accelerating domains cannot be ruled out in models converging to an Einstein de Sitter background and in domains undergoing gravitational collapse, the conditions for this are very restrictive. The results obtained may provide important theoretical clues on the effects of back-reaction and averaging in more general non-spherical models.

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