二元波暗物質的宇宙學模擬

Abstract

波暗物質模型提出暗物質是由質量約$10^{-22}$eV的極輕粒子作構成。而在過往波暗物質的相關研究中，主要集中在討論只有一種粒子組成的情況。在本研究中，我們要探討波暗物質包含兩種不同質量的粒子組成的情況，以數值模擬進行宇宙學的演化，並分析此情況下形成的孤立子與暗物質暈的特徵。我們假設波暗物質的總質量密度其中$75\%$為主要組成粒子，其中$25\%$為次要組成粒子。兩種波暗物質組成粒子只透過共同的重力互相影響。主要組成的粒子質量$m_{major}$ 為 $1\times10^{-22}$eV。次要組成的粒子質量$m_{minor}$ 為 $ \frac{1}{3}\times10^{-22}$ eV 或 $3\times10^{-22}$ eV。我們發現當粒子質量比$\frac{m_{major}}{m_{minor}}=3$時，兩種波暗物質的孤立子可以同時存在。在每個暗物質暈中，次要組成形成的孤立子有比較低的峰值密度且半徑大約是主要組成形成的孤立子的三倍。而且，形成的總密度分佈會比單一粒子組成的情況更平緩。另一方面，粒子質量比$\frac{m_{major}}{m_{minor}}=\frac{1}{3}$時，次要組成的孤立子將無法形成，這是因為主要組成的孤立子的重力位能得得環境變得太熱。

The wave dark matter model proposes particles with masses around $10^{-22}$ eV as dark matter candidates. Unlike previous researches that focus on the single-component situation, we explore the scenario that the wave dark matter consists of the two components with different particle masses and investigate the properties of their solitons and halos via cosmological simulations. We assume wave dark matter has $75\%$ of major component and $25\%$ of minor component in total mass density. The two components are coupled only through a common gravitational potential. The major-component particle mass $m_{major}$ is $1\times10^{-22}$ eV and the minor-component particle mass $m_{minor}$ is $ \frac{1}{3}\times10^{-22}$ eV or $3\times10^{-22}$ eV. We find that solitons of both components can coexist when $\frac{m_{major}}{m_{minor}}=3$. In every halo, the minor-component soliton is lower in peak density but three times larger in core radius compared to the major-component one. Furthermore, the resulting total density profiles are smoother than the single-component results. On the other hand, for $\frac{m_{major}}{m_{minor}}=\frac{1}{3}$, the minor-component soliton cannot form since the environment is hot due to the potential of the major-component soliton.