Uncertainty-Aware Neural Networks for Fuzzy Dark Matter Model Selection from x HIxHI Measurements
Abstract
The nature of dark matter remains a central question in cosmology, with fuzzy dark matter (FDM) models offering a compelling alternative to the cold dark matter (CDM) paradigm. We explore FDM scenarios by performing 21-cm simulations across a parameter space with f FDM ∈ [0.02, 0.10]fFDM in [0.02, 0.10] and m FDM ∈ [10-24, 10-21]\,eVmFDM in [10-24, 10-21] eV, obtaining global neutral hydrogen fractions (x HIxHI) for each model. Observational x HIxHI data and associated uncertainties from JWST are incorporated by estimating full probability density functions (PDFs) for both x HIxHI and redshift zz using Bayesian inference with the No-U-Turn Sampler (NUTS), yielding non-Gaussian multivariate uncertainty distributions. A hybrid machine learning framework is then trained on these observational PDFs to learn both central values and correlated uncertainties in x HIxHI and zz, iteratively refining its parameters in each training epoch through direct incorporation of the multivariate PDFs derived from observational constraints. We then compare the simulation outputs to the machine-learned observational trends to identify the most consistent models. Our results indicate that FDM models with m FDM 10-22\,eVmFDM approx 10-22 eV and f FDM 0.04fFDM approx 0.04 best match current data, while lighter masses are strongly constrained. By integrating simulations and machine learning in an uncertainty-aware framework, this work explores the physics of the early Universe and guides future studies of 21-cm cosmology and reionization.
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