Lyman-$α$ Forest Signatures of Mixed Fuzzy and Cold Dark Matter
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2026
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| author | Wang, Yourong Frank |
| author_facet | Wang, Yourong Frank |
| contents | We investigate Lyman-alpha forest flux statistics in mixed fuzzy dark matter (FDM) and cold dark matter (CDM) cosmologies using the Fluctuating Gunn-Peterson Approximation (FGPA) applied to hybrid Schrödinger-Poisson and N-body simulations. We evolve the dark matter distribution from z = 120 to z = 2 for an axion mass ( m_22 = 0.01) and FDM fraction (f_A = 0.1), and compare two realizations with identical initial conditions: one evolved with a particle-only approximation and one with full wave--mechanical dynamics.
We find that, despite near-degeneracy in the nonlinear matter power spectrum, the corresponding Ly α flux power spectra differ at the 10 percent level on intermediate scales. This discrepancy arises from a strong suppression of small-scale velocity power in the Schrödinger--Poisson evolution, which is not captured by N-body treatments with matched initial transfer functions. As a result, the flux statistics cannot be fully characterized by the matter power spectrum alone, but depend sensitively on the dynamical evolution of the velocity field. These results demonstrate that wave-mechanical effects in FDM leave distinct kinematic imprints in Ly α observables beyond those associated with initial-condition suppression. While our analysis is based on an idealized FGPA framework, it isolates a mechanism by which mixed dark matter models can break degeneracies present in standard structure-based probes, motivating further investigation with full hydrodynamical simulations. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_06038 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Lyman-$α$ Forest Signatures of Mixed Fuzzy and Cold Dark Matter Wang, Yourong Frank Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies We investigate Lyman-alpha forest flux statistics in mixed fuzzy dark matter (FDM) and cold dark matter (CDM) cosmologies using the Fluctuating Gunn-Peterson Approximation (FGPA) applied to hybrid Schrödinger-Poisson and N-body simulations. We evolve the dark matter distribution from z = 120 to z = 2 for an axion mass ( m_22 = 0.01) and FDM fraction (f_A = 0.1), and compare two realizations with identical initial conditions: one evolved with a particle-only approximation and one with full wave--mechanical dynamics. We find that, despite near-degeneracy in the nonlinear matter power spectrum, the corresponding Ly α flux power spectra differ at the 10 percent level on intermediate scales. This discrepancy arises from a strong suppression of small-scale velocity power in the Schrödinger--Poisson evolution, which is not captured by N-body treatments with matched initial transfer functions. As a result, the flux statistics cannot be fully characterized by the matter power spectrum alone, but depend sensitively on the dynamical evolution of the velocity field. These results demonstrate that wave-mechanical effects in FDM leave distinct kinematic imprints in Ly α observables beyond those associated with initial-condition suppression. While our analysis is based on an idealized FGPA framework, it isolates a mechanism by which mixed dark matter models can break degeneracies present in standard structure-based probes, motivating further investigation with full hydrodynamical simulations. |
| title | Lyman-$α$ Forest Signatures of Mixed Fuzzy and Cold Dark Matter |
| topic | Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2604.06038 |