STAR NRE: Solving supernova selection effects with set-based truncated auto-regressive neural ratio estimation

TL;DR

STAR NRE is a scalable, simulation-based neural ratio estimation method that effectively accounts for supernova selection effects, enabling unbiased cosmological inference from large photometric surveys.

Contribution

It introduces a set-based truncated auto-regressive neural ratio estimation approach that scales to large datasets and complex selection functions in supernova cosmology.

Findings

Achieves unbiased cosmological parameter inference from ~100,000 mock supernovae.

Handles complex selection criteria including transient classification.

Demonstrates precise inference of redshift evolution of supernova rates.

Abstract

Accounting for selection effects in supernova type Ia (SN Ia) cosmology is crucial for unbiased cosmological parameter inference -- even more so for the next generation of large, mostly photometric-only surveys. The conventional "bias correction" procedure has a built-in systematic bias towards the fiducial model used to derive it and fails to account for the additional Eddington bias that arises in the presence of significant redshift uncertainty. On the other hand, likelihood-based analyses within a Bayesian hierarchical model, e.g. using MCMC, scale poorly with the data set size and require explicit assumptions for the selection function that may be inaccurate or contrived. To address these limitations, we introduce STAR NRE, a simulation-based approach that makes use of a conditioned deep set neural network and combines efficient high-dimensional global inference with subsampling-based truncation in order to scale to very large survey sizes while training on sets with varying cardinality. Applying it to a simplified SN Ia model consisting of standardised brightnesses and redshifts with Gaussian uncertainties and a selection procedure based on the expected LSST sensitivity, we demonstrate precise and unbiased inference of cosmological parameters and the redshift evolution of the volumetric SN Ia rate from ~100 000 mock SNae Ia. Our inference procedure can incorporate arbitrarily complex selection criteria, including transient classification, in the forward simulator and be applied to complex data like light curves. We outline these and other steps aimed at integrating STAR NRE into an end-to-end simulation-based pipeline for the analysis of future photometric-only SN Ia data.