Local Nonlinear Transforms Effectively Extract Cosmological Information From Large-Scale Structure

Abstract

Extracting cosmological information from nonlinear and non-Gaussian large-scale structure remains a major challenge. We introduce the (Zel'dovich-inspired) ZI transform, a simple one-parameter local nonlinear transform in which $\eta$ controls the weighting of higher-order information in the transformed density field. For $\eta\geq3$, the transform can substantially suppress gravitational non-Gaussianity. Using the \textsc{Quijote} suite and Fisher information analysis over summed neutrino mass $M_\nu$, primordial non-Gaussianity $f_\mathrm{NL}$ with different shapes, and $\Lambda$CDM parameters, we find that the joint data vector of three transformed-field power spectra with $\{\eta=\infty, 6, 3\}$, denoted $P_\mathrm{ZI}$, tightens all constraints relative to the ordinary power spectrum, especially boosting the constraining power by factors of $290$ for $f_\mathrm{NL}^\mathrm{local}$ and $107$ for $M_\nu$, while yielding nearly unbiased parameter estimates. Compared further with other statistics beyond the ordinary power spectrum, $P_\mathrm{ZI}$ stands out as a powerful cosmological probe.