SimBIG: mock challenge for a forward modeling approach to galaxy clustering

Simulation-Based Inference of Galaxies (${\rm S{\scriptsize IM}BIG}$) is a forward modeling framework for analyzing galaxy clustering using simulation-based inference. In this work, we present the ${\rm IM}BIG}$ model, which designed to match observed SDSS-III BOSS CMASS sample. The model based on high-resolution Q{\scriptsize UIJOTE}}$ $N$-body simulations and flexible halo occupation model. It includes full survey realism models observational systematics such as angular masking fiber collisions. We "mock challenge" validating accuracy posteriors inferred from suite 1,500 test constructed with different simulation, finder, prescription. As demonstration IM}BIG}$, analyze power spectrum multipoles out $k_{\rm max} = 0.5\,h/{\rm Mpc}$ infer posterior $\Lambda$CDM cosmological parameters. Based mock challenge, find that our constraints $\Omega_m$ $\sigma_8$ are unbiased, but conservative. Hence, challenge demonstrates provides robust inferring parameters non-linear scales complete handling systematics. subsequent will use summary statistics beyond including bispectrum, marked spectrum, skew wavelet statistics, field-level statistics.