标题： 一种在修改引力中宇宙扰动的实用方法 显示英文标题

标题： A practical approach to cosmological perturbations in modified gravity

摘要： 下一代大规模调查不仅将在广义相对论框架内测量宇宙学参数，还将允许对框架本身进行精确测试。 在线性扰动的阶次上，LCDM模型中增长的偏离可以用两个关于时间和傅里叶数k的时间函数来量化。我们认为，在局部引力理论中，在准静态近似下，这些函数必须是k的多项式的比值，其中一个函数的分子等于另一个函数的分母。 此外，实际上所有目前考虑的可行模型中的多项式都是偶次且二次的。 这意味着，为了不显著损失一般性，可以使用数据仅约束五个单变量函数，而不是两个双变量函数。 此外，由于这五个函数预计变化缓慢，可以借助显式的平滑先验以非参数方式对它们进行拟合。 我们讨论了这种参数化在预测和拟合中的实际应用。 显示英文摘要

摘要： The next generation of large scale surveys will not only measure cosmological parameters within the framework of General Relativity, but will also allow for precision tests of the framework itself. At the order of linear perturbations, departures from the growth in the LCDM model can be quantified in terms of two functions of time and Fourier number k. We argue that in local theories of gravity, in the quasi-static approximation, these functions must be ratios of polynomials in k, with the numerator of one function being equal to the denominator of the other. Moreover, the polynomials are even and of second degree in practically all viable models considered today. This means that, without significant loss of generality, one can use data to constraint only five functions of a single variable, instead of two functions of two variables. Furthermore, since the five functions are expected to be slowly varying, one can fit them to data in a non-parametric way with the aid of an explicit smoothness prior. We discuss practical application of this parametrization to forecasts and fits.