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arXiv 1507.05565astro-ph.COgr-qchep-th
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大爆炸核合成过程中修正的Gauss-Bonnet引力的约束

Constraints on modified Gauss-Bonnet gravity during big bang nucleosynthesis

Motohiko Kusakabe, Seoktae Koh, K. S. Kim, Myung-Ki Cheoun

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29 pages, 24 figures
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摘要：

修正的引力被认为是对现在和早期宇宙加速膨胀的可能解释之一。研究了修正引力对大爆炸核合成的影响。如果在BBN时期修正重力的影响是显着的，它们应该被观察到的原始轻元素丰度的变化。我们假设在BBN时期期间具有高斯-邦内项$G$的$f(G)$项。对于函数$f(G)$，假设$df/dG \propto t^p$的幂律关系，其中$t$是宇宙时间。数值求解了$f(G)$重力模型中BBN过程中物理量的时间演化，并对计算结果进行了分析。发现在某些参数范围内，宇宙膨胀率的正确解可能会丢失。此外，我们表明，原始轻元素丰度的计算结果可以显着不同的观测数据。特别是，原始D丰度的观测极限导致对$f(G)$引力的最强约束。然后，我们推导出的$f(G)$重力的参数的限制，考虑到存在的解决方案的膨胀率和最终的轻元素丰度。

英文摘要：

The modified gravity is considered to be one of possible explanations of the accelerated expansions of the present and the early universe. We study effects of the modified gravity on big bang nucleosynthesis (BBN). If effects of the modified gravity are significant during the BBN epoch, they should be observed as changes of primordial light element abundances. We assume a $f(G)$ term with the Gauss-Bonnet term $G$, during the BBN epoch. A power-law relation of $df/dG \propto t^p$ where $t$ is the cosmic time was assumed for the function $f(G)$ as an example case. We solve time evolutions of physical variables during BBN in the $f(G)$ gravity model numerically, and analyzed calculated results. It is found that a proper solution for the cosmic expansion rate can be lost in some parameter region. In addition, we show that calculated results of primordial light element abundances can be significantly different from observational data. Especially, observational limits on primordial D abundance leads to the strongest constraint on the $f(G)$ gravity. We then derive constraints on parameters of the $f(G)$ gravity taking into account the existence of the solution of expansion rate and final light element abundances.

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