标题： 尘宇宙中的不均匀性——暗能量的可能替代方案？ 显示英文标题

标题： Inhomogeneities in dusty universe - a possible alternative to dark energy?

摘要： 近年来，关于不均匀性在解释宇宙晚期加速膨胀中的作用重新引起了讨论。 我们在球对称但非均匀的 Lemaitre-Tolman-Bondi (LTB) 模型的基础上，借助解析方法研究了这一问题，并将其推广到高维情况。 观察发现，与 Kolb 等人的主张相反，如果物质场满足能量条件，则不均匀性和额外维度的存在并不能反转减速参数的符号。 著名的 Raychaudhuri 方程也指向同样的结果。 然而，无需明确求解场方程即可证明，尽管总减速率在所有地方都为正，但这并不排除在纯尘宇宙中存在径向加速的可能性——只要角尺度因子减速足够快即可，反之亦然。 此外还发现，引入额外维度并不能改变这种情形，反而实际上有助于减速过程。 显示英文摘要

摘要： There have been of late renewed debates on the role of inhomogeneities to explain the observed late acceleration of the universe. We have looked into the problem analytically with the help of the well known spherically symmetric but inhomogeneous Lemaitre-Tolman-Bondi(LTB) model generalised to higher dimensions. It is observed that in contrast to the claim made by Kolb et al the presence of inhomogeneities as well as extra dimensions can not reverse the signature of the deceleration parameter if the matter field obeys the energy conditions. The well known Raychaudhuri equation also points to the same result. Without solving the field equations explicitly it can, however, be shown that although the total deceleration is positive everywhere nevertheless it does not exclude the possibility of having radial acceleration, even in the pure dust universe, if the angular scale factor is decelerating fast enough and vice versa. Moreover it is found that introduction of extra dimensions can not reverse the scenario. To the contrary it actually helps the decelerating process.