论文标题

$λ$ CDM宇宙中LSS的摄动理论:精确的时间演变和两循环功率谱

Perturbation theory of LSS in the $Λ$CDM Universe: exact time evolution and the two-loop power spectrum

论文作者

Fasiello, Matteo, Fujita, Tomohiro, Vlah, Zvonimir

论文摘要

我们为$λ$ CDM宇宙学的Eulerian Standard扰动理论中的所有订单中的密度和速度字段提供了精确的分析解决方案。特别是,我们表明,密度和速度场内核可以在每个扰动顺序上以时间和动量为单位写入。内核溶液是由动量运算符及其时间相关系数的分析基础构建的,该系数求解了一组递归微分方程。我们还为此类系数提供了精确的封闭扰动解决方案,并围绕(准)EDS近似扩展。我们发现,扰动解决方案迅速收敛于数值获得的解决方案,其领先顺序结果足以满足任何实际要求。为了说明我们的发现,我们计算了$λ$ CDM宇宙学中的确切的两环暗物质密度和速度功率谱。我们表明,确切的$λ$ CDM与(准)EDS近似结果之间的差异可以达到数百分之几的水平(在Redshift Zero中,对于WaveNumbers $ k <1h/$ mpc)。可以通过用EFT对抗来利用堕落性来部分缓解这种偏差。作为我们算法对于时间相关系数解决方案的另一个好处,$λ$ CDM中的功率光谱循环的计算复杂性与EDS案例相当。在执行两循环计算时,我们设计了一种明确的方法来实施所谓的IR取消,以及由于质量和动量保护而产生的取消方法。

We derive exact analytic solutions for density and velocity fields to all orders in Eulerian standard perturbation theory for $Λ$CDM cosmology. In particular, we show that density and velocity field kernels can be written in a separable form in time and momenta at each perturbative order. The kernel solutions are built from an analytic basis of momentum operators and their time-dependent coefficients, which solve a set of recursive differential equations. We also provide an exact closed perturbative solution for such coefficients, expanding around the (quasi-)EdS approximation. We find that the perturbative solution rapidly converges towards the numerically obtained solutions and its leading order result suffices for any practical requirements. To illustrate our findings, we compute the exact two-loop dark matter density and velocity power spectra in $Λ$CDM cosmology. We show that the difference between the exact $Λ$CDM and the (quasi-)EdS approximated result can reach the level of several percent (at redshift zero, for wavenumbers $k<1h/$Mpc). This deviation can be partially mitigated by exploiting the degeneracy with the EFT counterterms. As an additional benefit of our algorithm for the solutions of time-dependent coefficients, the computational complexity of power spectra loops in $Λ$CDM is comparable to the EdS case. In performing the two-loop computation, we devise an explicit method to implement the so-called IR cancellations, as well as the cancellations arising as a consequence of mass and momentum conservation.

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