A Universal Bilinear Model for the Dependence of Void Asymmetry Distributions on $Omega_{m}$ and $sigma_{8}$

A Universal Bilinear Model for the Dependence of Void Asymmetry Distributions on $Omega_{m}$ and $sigma_{8}$
Geonwoo Kang (Seoul National University), Jounghun Lee (Seoul National University)
arXiv:2601.06589v2 Announce Type: replace
Abstract: $Aims$: We present a new independent diagnostics based on void properties, by which the matter density parameter ($Omega_{m}$) and amplitude of initial density field ($sigma_{8}$) can be constrained. This diagnostics utilizes coherent rotation of void galaxies, which can be observed as redshift asymmetry in opposite sides bisected by the projected spin axes of hosting voids.
$Methods$: Identifying the voids and their member galaxies in the AbacusSummit of cosmological simulations and searching for their projected spin axes with an iterative method, we numerically determine the void asymmetry distributions both in real and redshift spaces for three different classes of the background cosmologies: the $Lambda$CDM, the $w$CDM and the $w_{0}w_{a}$CDM.
$Results$: It is discovered that the void asymmetry distributions in real and redshift spaces are well approximated by the generalized Gamma models characterized by the scale and shape parameters for all of the $33$ background cosmologies considered. It turns out that the initial conditions affect only the scale parameter of the void asymmetry distributions that exhibits an almost linear dependence on each of $Omega_{m}$ and $sigma_{8}$ with being insensitive to $w$. Developing a bilinear model for the dependence of void asymmetry distributions on $Omega_{m}$ and $sigma_{8}$, we show that its coefficients are universal constants over the three cosmological classes.
$Conclusions$: Given that the void asymmetry distributions in redshift space are readily measurable properties, our universal model for the shape parameter of the void asymmetry distributions will in principle complement the standard cosmological diagnostics to break the $Omega_{m}$-$sigma_{8}$ degeneracy, regardless of $w$.arXiv:2601.06589v2 Announce Type: replace
Abstract: $Aims$: We present a new independent diagnostics based on void properties, by which the matter density parameter ($Omega_{m}$) and amplitude of initial density field ($sigma_{8}$) can be constrained. This diagnostics utilizes coherent rotation of void galaxies, which can be observed as redshift asymmetry in opposite sides bisected by the projected spin axes of hosting voids.
$Methods$: Identifying the voids and their member galaxies in the AbacusSummit of cosmological simulations and searching for their projected spin axes with an iterative method, we numerically determine the void asymmetry distributions both in real and redshift spaces for three different classes of the background cosmologies: the $Lambda$CDM, the $w$CDM and the $w_{0}w_{a}$CDM.
$Results$: It is discovered that the void asymmetry distributions in real and redshift spaces are well approximated by the generalized Gamma models characterized by the scale and shape parameters for all of the $33$ background cosmologies considered. It turns out that the initial conditions affect only the scale parameter of the void asymmetry distributions that exhibits an almost linear dependence on each of $Omega_{m}$ and $sigma_{8}$ with being insensitive to $w$. Developing a bilinear model for the dependence of void asymmetry distributions on $Omega_{m}$ and $sigma_{8}$, we show that its coefficients are universal constants over the three cosmological classes.
$Conclusions$: Given that the void asymmetry distributions in redshift space are readily measurable properties, our universal model for the shape parameter of the void asymmetry distributions will in principle complement the standard cosmological diagnostics to break the $Omega_{m}$-$sigma_{8}$ degeneracy, regardless of $w$.