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arXiv · 2608.15635

Modelling the nonlinear matter power spectrum in Hu-Sawicki $f(R)$ gravity with the Web-Halo Model

Xin Wang·Zhiqi Huang
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Abstract

We develop a semi-analytic extension of the Web-Halo Model (WHM) to Hu-Sawicki $f(R)$ gravity, with the aim of linking nonlinear matter clustering to the successive stages of cosmic-web collapse. The cylindrical sheet and filament windows of the original WHM are replaced by axisymmetric ellipsoidal top-hat windows, yielding a modest improvement around the perturbative-to-nonlinear transition without introducing additional fitting parameters. Modified gravity is incorporated through environment-dependent chameleon spherical collapse, from which the collapse threshold and virial overdensity are obtained and propagated through the sheet, filament, and halo contributions. For $|f_{R0}|=10^{-5}$ and $10^{-6}$, the predicted nonlinear enhancement is broadly consistent with the scale-, redshift-, and field-strength dependence seen in the e-MANTIS emulator, with closer agreement for the weaker field and at higher redshift. The component responses show that sheets and filaments contribute substantially around the transition regime, while the halo response becomes increasingly important at smaller scales. As complementary diagnostics, no displacement of the BAO peak is resolved, whereas tomographic weak-lensing spectra retain a percent-level response to the modified matter power spectrum. The extended WHM therefore provides a physically interpretable framework for tracing screened modified-gravity effects across the cosmic-web collapse hierarchy.

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Xin Wang, Zhiqi Huang. 2026-08-16. Modelling the nonlinear matter power spectrum in Hu-Sawicki $f(R)$ gravity with the Web-Halo Model. https://arxiv.org/abs/2608.15635

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