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arXiv 2004.02896gr-qcastro-ph.COhep-th
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多重分数时空中的暗能量

Dark energy in multi-fractional spacetimes

Gianluca Calcagni, Antonio De Felice

摘要:

我们研究的可能性,以获得宇宙学晚时间加速从几何形状的尺度变化,特别是在所谓的多重分数阶理论与$q$ -衍生物和加权导数。在$q$ -导数的理论中,光度距离与广义相对论中的相同,因此几何不能作为暗能量。在加权导数理论中,几何本身就能够维持一个晚期加速阶段而无需微调,同时与结构形成和大爆炸核合成边界兼容。这意味着以一种自然的方式将理论从小尺度扩展到大尺度的引力修正。令人惊讶的是,时空的豪斯多夫维数被限制为接近拓扑维数4。在论证了这一发现可能不是数值上的巧合之后,我们得出结论,现在的加速度可以被看作是时空几何的一个新的恢复定律的影响。

英文摘要:

We study the possibility to obtain cosmological late-time acceleration from a geometry changing with the scale, in particular, in the so-called multifractional theories with $q$-derivatives and with weighted derivatives. In the theory with $q$-derivatives, the luminosity distance is the same as in general relativity and, therefore, geometry cannot act as dark energy. In the theory with weighted derivatives, geometry alone is able to sustain a late-time acceleration phase without fine tuning, while being compatible with structure-formation and big-bang nucleosynthesis bounds. This suggests to extend the theory, in a natural way, from just small-scale to also large-scale modifications of gravity. Surprisingly, the Hausdorff dimension of spacetime is constrained to be close to the topological dimension 4. After arguing that this finding might not be a numerical coincidence, we conclude that present-day acceleration could be regarded as the effect of a new restoration law for spacetime geometry.

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