AI 中文总结
本文提出有效场论形式体系，扩展轴子相对论行为建模至同步规范及含各向异性应力的牛顿规范，提出轴子场可视为完美流体的诠释，为宇宙学玻尔兹曼求解器纳入轴子奠定理论基础。
AI 中文摘要
在这项工作中，我们提出了一种形式体系来模拟轴子的相对论行为。轴子的相对论行为精确建模出奇地困难，因为它涉及远短于哈勃时间尺度的振荡。为克服这一挑战，通常需要诉诸某种有效处理，仅关注精确振荡的时间平均描述。Salehian、Namjoo 与 Kaiser 基于有效场论形式体系，为此类处理提供了系统框架。尽管上述研究是在无各向异性应力的牛顿规范下针对轴子扰动提出的，我们将该形式体系扩展到同步规范，后者在现实宇宙学背景的数值实现中更为常用。然而，与他们的工作不同，我们提出一种流体诠释，其中轴子场在所有时刻均可视为完美流体，无论是在精确还是有效范围内。此外，我们给出了具有非零各向异性应力的牛顿规范的有效场论，使原始形式体系更加通用，并适用于宇宙物质内容为多组分的情景。这些结果为配套论文奠定了理论基础，在配套论文中我们讨论了轴子场应如何与常见宇宙学玻尔兹曼求解器中的其他物种一同纳入。
英文摘要
In this work, we present a formalism to model the relativistic behavior of axions. The relativistic behavior of axions is surprisingly difficult to model precisely, as it involves oscillations on timescales much shorter than the Hubble timescale. To overcome this challenge, one typically resorts to some form of effective treatment, focusing only on the time-averaged description of the exact oscillations. Salehian, Namjoo & Kaiser provide a systematic framework for such treatment, based on the effective field theory formalism. While the aforementioned study was formulated for axion perturbations in the Newtonian gauge with no anisotropic stress, we extend the formalism to the synchronous gauge that is more conventionally used for numerical implementation in a realistic cosmological setting. Unlike their work, however, we propose a fluid interpretation in which the axion field can be identified as a perfect fluid at all times, both in the exact and effective regimes. Moreover, we present the effective field theory for the Newtonian gauge with non-zero anisotropic stress, making the original formulation more general and useful for scenarios where the matter content of the universe is multi-component. These results lay the theoretical foundation for a companion paper where we discuss how the axion field should be incorporated alongside other species in common cosmological Boltzmann solvers.
Comments20 pages, 1 figure. Small update to get the correct reference to the companion paper
