New Method for Reconstructing Initial Cosmic Matter Fields from Weak-Lensing Observations
Researchers have developed a field-level likelihood model that reconstructs the universe's initial matter density conditions from two-dimensional projected fields used in weak-lensing and photometric galaxy surveys. Unlike the full 3D case, 2D projected fields are only fully determined by their initial counterparts at linear order, with non-linear contributions from the entire volume introducing statistical uncertainty. The work advances cosmological inference by enabling initial-field reconstruction even in the presence of complex observational masks.
A new study submitted to the Journal of Cosmology and Astroparticle Physics (JCAP) presents a theoretical and computational framework for performing field-level inference on two-dimensional projected cosmological matter density fields. While the full 3D evolved matter density field is deterministically set by its initial conditions at fixed cosmological parameters, the 2D projected version loses this determinism at non-linear scales, where modes from the entire initial volume contribute. The authors model the evolved projected field as deterministic in the initial projected density field but probabilistic with respect to the remaining out-of-plane modes. Predictions derived from Lagrangian Perturbation Theory (LPT) are validated against an ensemble of N-body simulations run with fixed projected initial conditions, showing good agreement and confirming that information about initial projected fields is exponentially suppressed on non-linear scales. The team implemented this framework in a likelihood code using Hamiltonian Monte Carlo sampling, demonstrating successful reconstruction of initial fields even when non-trivial survey mask features are present. The significantly revised second version expands the paper from 13 to 20 pages and 4 to 11 figures, adding a full likelihood implementation based on 2D LPT.
What's missing
The study is a preprint that has not yet completed peer review at JCAP. The paper does not report tests on realistic survey noise levels, photometric redshift uncertainties, or baryonic feedback effects, which could affect applicability to real weak-lensing datasets such as those from Euclid or the Rubin Observatory. The scalability of the Hamiltonian Monte Carlo approach to full-survey data volumes is not assessed.
What different sources said
- arXiv astro-phCenter
Field-level likelihood for projected fields: Evolved projected fields from initial projected fields
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