BibTeX

@article{2406.06067v1,
Author        = {Christopher Wilson and Rachel bean},
Title         = {Fisher's Mirage: Noise Tightening of Cosmological Constraints in
  Simulation-Based Inference},
Eprint        = {2406.06067v1},
ArchivePrefix = {arXiv},
PrimaryClass  = {astro-ph.CO},
Abstract      = {We systematically analyze the implications of statistical noise within
numerical derivatives on simulation-based Fisher forecasts for large scale
structure surveys. Noisy numerical derivatives resulting from a finite number
of simulations, $N_{sims}$, act to bias the associated Fisher forecast such
that the resulting marginalized constraints can be significantly tighter than
the noise-free limit. We show the source of this effect can be traced to the
influence of the noise on the marginalization process. Parameters such as the
neutrino mass, $\M$, for which higher-order forward differentiation schemes are
commonly used, are more prone to noise; the predicted constraints can be akin
to those purely from a random instance of statistical noise even using
$(1\mathrm{Gpc}/h)^{3}$ simulations with $N_{sims}=500$ realizations. We
demonstrate how derivative noise can artificially reduce parameter degeneracies
and seemingly null the effects of adding nuisance parameters to the forecast,
such as HOD fitting parameters. We mathematically characterize these effects
through a full statistical analysis, and demonstrate how confidence intervals
for the true noise-free, $N_{sims} \rightarrow \infty$, Fisher constraints can
be recovered even when noise comprises a consequential component of the
measured signal. The findings and approaches developed here are important for
ensuring simulation-based analyses can be accurately used to assess upcoming
survey capabilities.},
Year          = {2024},
Month         = {Jun},
Url           = {http://arxiv.org/abs/2406.06067v1},
File          = {2406.06067v1.pdf}
}