Balancing bias, baryons, and scale cuts in LSST 3x2pt analysis
Abstract
Stage IV surveys such as LSST will probe deeply into the nonlinear regime, where systematic effects from galaxy bias and baryonic feedback become dominant and poorly constrained nuisance parameters can lead to degeneracies. In this work we present a 3x2pt analysis for LSST Y1 and Y10 data using the BACCO emulator for modelling both the hybrid-effective field theory (HEFT) for nonlinear galaxy bias and the baryonic feedback using the baryonification mechanism. We aim to find a balance between model complexity and scale cuts, with particular attention to parameter degeneracies and baryonic feedback effects on the galaxy-matter and galaxy-galaxy power spectra. First, we find that a linear bias model delivers percent-level unbiased constraints on Ωm and σ8 only up to kmax=0.1 h/Mpc, but pushing to smaller scales requires a perturbative approach. Second, we compare HEFT with a minimal bias variant with fixed higher-order terms, and find that the latter is unbiased in ΛCDM even at kmax=0.7 h/Mpc. We show that higher-order bias can mimic baryonic suppression, but baryons cannot reproduce the full range of higher-order bias behaviour within the parameter range allowed by the BACCO baryonification model. Third, we find that a detection of the total neutrino mass Mν is possible for both Y1 and Y10 for k ≥ 0.5 h/Mpc, at least when photo-z uncertainties and related nuisance parameters are precisely known. However, the specific measured value is not robust across equally plausible mock scenarios: the inferred Mν can be significantly biased by adopting the minimal bias model. The entire analysis is conducted with a new independent, open source pipeline MGL that we present for the first time in this work.
Related
- Heavy Dark Baryons as Self-Interacting Dark Matter: A GeV-Scale Coincidence
- Tide-and-Seek: Anisotropic scale-dependent bias in the Lyman-alpha forest and designer samples
- Merlin: Fast and flexible 3x2pt cosmology with simulation-based inference
- Connecting the Dots: Prospects for Detecting Multi-Source Inflation through Scale-Dependent and Stochastic Bias of Little Red Dots
- Finding the distribution of matter using lenses - II: deconvolution-based reconstruction with 3x2pt measurements
BibTeX
@misc{truttero2026balancing,
title = {{Balancing bias, baryons, and scale cuts in LSST 3x2pt analysis}},
author = {Ottavia Truttero and Maria Tsedrik and Joe Zuntz and Alkistis Pourtsidou and Nikolina Šarčević and Christos Georgiou and the LSST Dark Energy Science Collaboration},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.10679},
eprint = {2606.10679},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.10679},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Balancing bias, baryons, and scale cuts in LSST 3x2pt analysis
AU - Ottavia Truttero
AU - Maria Tsedrik
AU - Joe Zuntz
AU - Alkistis Pourtsidou
AU - Nikolina Šarčević
AU - Christos Georgiou
AU - the LSST Dark Energy Science Collaboration
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2606.10679
UR - https://arxiv.org/abs/2606.10679
AB - Stage IV surveys such as LSST will probe deeply into the nonlinear regime, where systematic effects from galaxy bias and baryonic feedback become dominant and poorly constrained nuisance parameters can lead to degeneracies. In this work we present a 3x2pt analysis for LSST Y1 and Y10 data using the BACCO emulator for modelling both the hybrid-effective field theory (HEFT) for nonlinear galaxy bias and the baryonic feedback using the baryonification mechanism. We aim to find a balance between model complexity and scale cuts, with particular attention to parameter degeneracies and baryonic feedback effects on the galaxy-matter and galaxy-galaxy power spectra. First, we find that a linear bias model delivers percent-level unbiased constraints on Ω_m and σ_8 only up to k_max=0.1 h/Mpc, but pushing to smaller scales requires a perturbative approach. Second, we compare HEFT with a minimal bias variant with fixed higher-order terms, and find that the latter is unbiased in ΛCDM even at k_max=0.7 h/Mpc. We show that higher-order bias can mimic baryonic suppression, but baryons cannot reproduce the full range of higher-order bias behaviour within the parameter range allowed by the BACCO baryonification model. Third, we find that a detection of the total neutrino mass M_ν is possible for both Y1 and Y10 for k ≥ 0.5 h/Mpc, at least when photo-z uncertainties and related nuisance parameters are precisely known. However, the specific measured value is not robust across equally plausible mock scenarios: the inferred M_ν can be significantly biased by adopting the minimal bias model. The entire analysis is conducted with a new independent, open source pipeline MGL that we present for the first time in this work.
ER -