Nested solitons in two-field fuzzy dark matter

• Published in: Monthly notices of the Royal Astronomical Society Vol. 527; no. 2; pp. 4162 - 4172
• Main Authors: Luu, Hoang Nhan, Mocz, Philip, Vogelsberger, Mark, May, Simon, Borrow, Josh, Tye, S-H Henry, Broadhurst, Tom
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 09.11.2023
• Subjects: ASTRONOMY AND ASTROPHYSICS; cosmology; dark matter; numerical; theory; methods: numerical; dark matter; cosmology: theory
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stad3482

Dark matter as scalar particles consisting of multiple species is well motivated in string theory where axion fields are ubiquitous. A two-field fuzzy dark matter (FDM) model features two species of ultralight axion particles with different masses, m1 ≠ m2, which is extended from the standard one-field model with $m_a \sim 10^{-22} \, {\rm eV}$. Here we perform numerical simulations to explore the properties of two-field FDM haloes. We find that the central soliton has a nested structure when m2 ≫ m1, which is distinguishable from the generic flat-core soliton in one-field haloes. However, the formation of this nested soliton is subject to many factors, including the density fraction and mass ratio of the two fields. Finally, we study non-linear structure formation in two-field cosmological simulations with self-consistent initial conditions and find that the small-scale structure in two-field cosmology is also distinct from the one-field model in terms of DM halo counts and soliton formation time.