Cosmic string loops are non-linear density fluctuations which form in the early universe and could play an important role in explaining many phenomena which are in tension with the standard ΛCDM model. Hence, the accretion process onto cosmic string loops should be studied in detail. Most previous works view loops as point masses and ignore the impact of a finite loop size. In this work, we utilize the Zel'dovich approximation to calculate the non-linear mass sourced by a static extended loop with a time-averaged density profile derived from the trajectory of the loop oscillation, and compare the result with what is obtained for a point-mass source. We find that the finite size of a loop mainly affects the evolution of turnaround shells during the early stages of accretion, converging to the point mass result after a critical redshift, zc ^{( II)/( III)}. For zc ^{( II)/( III)}, the total accreted mass surrounding a loop is suppressed relative to the point mass case and has a growth rate proportional to (1+z)^-3/2. As an immediate extension, we also qualitatively analyse the accretion onto moving point masses and onto moving extended loops. In addition to the reduction in the nonlinear mass, the loop finite size also changes the shape of the turnaround surface at early stages of accretion.

中文翻译：

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吸积到振荡的宇宙弦环上


宇宙弦环是在早期宇宙中形成的非线性密度涨落，在解释许多与标准 ΛCDM 模型存在矛盾的现象方面可以发挥重要作用。因此，应该详细研究宇宙弦环上的吸积过程。大多数先前的工作将循环视为点质量，并忽略有限循环大小的影响。在这项工作中，我们利用 Zel'dovich 近似来计算由静态扩展环路产生的非线性质量，该环路具有从环路振荡轨迹得出的时间平均密度分布，并将结果与​​从点质量源。我们发现，环的有限尺寸主要影响吸积早期阶段转向壳层的演化，在临界红移后收敛到点质量结果， zc ^(二)/(三) 。为了zc ^{( II)/( III)} ，围绕环的总吸积质量相对于点质量情况受到抑制，并且增长率与 (1+ z ) ^-3/2 。作为直接扩展，我们还定性分析了移动点质量和移动扩展环上的吸积。除了非线性质量的减少之外，环有限尺寸还改变了吸积早期阶段的转向表面的形状。