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arXiv 1503.01374gr-qc
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自作用力与后牛顿动力学的比较:超越圆轨道

Comparison Between Self-Force and Post-Newtonian Dynamics: Beyond Circular Orbits

Sarp Akcay, Alexandre Le Tiec, Leor Barack, Norichika Sago, Niels Warburton

摘要:

引力自作用力(GSF)和后牛顿(PN)方案是用于模拟紧凑二元系统动力学的互补近似方法。在有效性的重叠域中比较它们的结果为这两种方法提供了关键的测试,并且可以用于提高它们的准确性,例如通过确定先前未知的PN参数。在这里,我们第一次将这种比较扩展到非圆轨道-具体地说,扩展到两个非自旋物体在一个约束(偏心)轨道上的系统。为了能够进行比较,我们使用了一个特定的轨道平均量$\langle U \rangle$,它推广了德特韦勒的红移不变量。函数关系$\langle U \rangle(Ω_r,Ω_ϕ)$是保守动力学的不变特征,其中$Ω_r$和$Ω_ϕ$是径向和方位运动的频率。我们计算$\langle U \rangle(Ω_r,Ω_ϕ)$数值通过线性顺序的质量比$q$,使用GSF代码,这是基于频域处理的线性化爱因斯坦方程的洛伦兹规范。我们还推导出$\langle U \rangle(Ω_r,Ω_ϕ)$解析通过3 PN顺序,对于任意$q$,使用已知的近区3 PN度量和广义准开普勒表示的运动。我们证明了分析PN预测的$\mathcal{O}(q)$片段与数值GSF结果完全一致,并且我们使用后者来估计在$\mathcal{O}(q)$的4PN表达的未知片段。

英文摘要:

The gravitational self-force (GSF) and post-Newtonian (PN) schemes are complementary approximation methods for modelling the dynamics of compact binary systems. Comparison of their results in an overlapping domain of validity provides a crucial test for both methods, and can be used to enhance their accuracy, e.g. via the determination of previously unknown PN parameters. Here, for the first time, we extend such comparisons to noncircular orbits---specifically, to a system of two nonspinning objects in a bound (eccentric) orbit. To enable the comparison we use a certain orbital-averaged quantity $\langle U \rangle$ that generalizes Detweiler's redshift invariant. The functional relationship $\langle U \rangle(Ω_r,Ω_ϕ)$, where $Ω_r$ and $Ω_ϕ$ are the frequencies of the radial and azimuthal motions, is an invariant characteristic of the conservative dynamics. We compute $\langle U \rangle(Ω_r,Ω_ϕ)$ numerically through linear order in the mass ratio $q$, using a GSF code which is based on a frequency-domain treatment of the linearized Einstein equations in the Lorenz gauge. We also derive $\langle U \rangle(Ω_r,Ω_ϕ)$ analytically through 3PN order, for an arbitrary $q$, using the known near-zone 3PN metric and the generalized quasi-Keplerian representation of the motion. We demonstrate that the $\mathcal{O}(q)$ piece of the analytical PN prediction is perfectly consistent with the numerical GSF results, and we use the latter to estimate yet unknown pieces of the 4PN expression at $\mathcal{O}(q)$.

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