arXiv 1506.032322015-06-10astro-ph.CO

FRCAMB：一个计算微波背景各向异性的$f(R)$程序

FRCAMB: An $f(R)$ Code for Anisotropies in the Microwave Background

Lixin Xu

备注：: 8 pages, 7 figures

摘要：

本文提出了一个$f(R)$引力模型来实现宇宙的晚期加速膨胀。为了检验$f(R)$引力模型在宇宙观测中的可行性，需要求解背景演化和Einstein-Boltzmann方程，研究背景演化对宇宙微波背景功率谱和物质功率谱的影响。在市场上，我们已经有了{ \bf CAMB}代码的修改版本，例如{ \bf EFTCAMB}和{ \bf MGCAMB}。然而，在这些公开可用的爱因斯坦-玻尔兹曼代码中，假设了特定的背景宇宙学，例如$Λ$ CDM或$w$ CDM。这个假设对于一个特定的$f(R)$模型是不恰当的，因为在这个模型中背景演化可能不同于$Λ$ CDM宇宙学。因此，本文的主要任务是在{ \bf CAMB}程序的基础上，提出一个计算任意$f(R)$重力模型的微波背景各向异性的程序，即{ \bf FRCAMB}，其中一致地包含了背景和扰动的演化。结果表明，只要输入$f(R)$函数及其对$R$的前两阶导数，即$f_R\equiv df/dR$、$f_{RR}\equiv d^2f/dR^2$和模型参数的合理值，就可以把{ \bf FRCAMB}当作黑箱，输出CMB功率谱和物质功率谱。作为副产品，还可以输出$f(R)$模型的有效状态方程，无量纲能量密度的演化和其他有趣的宇宙学量。

英文摘要：

An $f(R)$ gravity model is proposed to realize a late time accelerated expansion of our Universe. To test the viability of an $f(R)$ gravity model through cosmic observations, the background evolution and the Einstein-Boltzmann equation should be solved for studying the effects on the cosmic microwave background power spectrum and on the matter power spectrum. In the market, we already have the modified versions of {\bf CAMB} code, for instance {\bf EFTCAMB} and {\bf MGCAMB}. However, in these publicly available Einstein-Boltzmann codes, a specific background cosmology, for example the $Λ$CDM or $w$CDM, is assumed. This assumption would be non-proper for a specific $f(R)$ model where the background evolution may be different from a $Λ$CDM cosmology. Therefore the main task for this paper is to present a code to calculate the anisotropies in the microwave background for any $f(R)$ gravity model based on {\bf CAMB} code, i.e. {\bf FRCAMB}, where the background and perturbation evolutions are included consistently. As results, one can treat {\bf FRCAMB} as a blackbox to output the CMB power spectrum and matter power spectrum, once an $f(R)$ function, its first two derivative with respect to $R$, i.e. $f_R\equiv df/dR$, $f_{RR}\equiv d^2f/dR^2$ and the reasonable values of the model parameters are inputted properly. As by-products, one can also output the effective equation of state of $f(R)$ model, the evolution of the dimensionless energy densities and other interesting cosmological quantities.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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