Oral Presentation

Reconstructing the Primordial Density Field with Differentiable N-body Simulations

Author(s): Sirawich Saranakomkoop (Nagoya University)

Presenter: Sirawich Saranakomkoop (Nagoya University)

In this study, we address the problem of reconstructing the initial density field of the universe by applying differentiable simulation techniques. Specifically, we implement pmwd (Particle-Mesh with Derivatives; Y. Li et al., ApJS, 2024), an adjoint-based differentiable N-body framework, to recover the primordial density field from evolved large-scale structures at redshift z = 0 obtained from the Indra simulation.
Our reconstructions show excellent agreement with target fields derived from the Indra simulation at z=0 for all the scales we explore. With iterative refinement of initial conditions, we improve the accuracy of the forward simulations, which leads to a closer alignment with the observed density field. Moreover, through reverse time integration, we recover the density field at higher redshifts (z = 10), especially on large scales, revealing meaningful similarities to the expected initial conditions. We find that increasing the simulation resolution improves the accuracy of the power spectrum on small scales at higher redshifts.