描述膨胀和加速膨胀开始的可行改良$f(R)$重力分类
Class of viable modified $f(R)$ gravities describing inflation and the onset of accelerated expansion
摘要：
在Jordan框架和Einstein框架下，发展了一种可行的修正$f(R)$引力的一般方法。介绍了一类指数型的、现实的修正引力，并仔细地进行了研究。特别关注的是步类模型，最有前途的唯象的观点，并提供了一个自然的方式来分类所有可行的修改重力。明确考虑一步和两步模型，但分析可扩展到$N$步模型。早期宇宙的暴胀和最近加速膨胀的开始都以一种自然的、统一的方式出现在这些模型中。此外，它表明，在这一类别中的模型很容易通过所有的本地测试，包括稳定的球体解决方案，不违反牛顿定律，并产生一个非常沉重的正质量的额外的标量自由度。
英文摘要：
A general approach to viable modified $f(R)$ gravity is developed in both the Jordan and the Einstein frames. A class of exponential, realistic modified gravities is introduced and investigated with care. Special focus is made on step-class models, most promising from the phenomenological viewpoint and which provide a natural way to classify all viable modified gravities. One- and two-steps models are explicitly considered, but the analysis is extensible to $N$-step models. Both inflation in the early universe and the onset of recent accelerated expansion arise in these models in a natural, unified way. Moreover, it is demonstrated that models in this category easily pass all local tests, including stability of spherical body solution, non-violation of Newton's law, and generation of a very heavy positive mass for the additional scalar degree of freedom.
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