paper

Tracing Signatures of Modified Gravity in Redshift-Space Galaxy Bispectrum Multipoles: Prospects for Euclid

arXiv:2508.19106 · doi:10.1103/gzk3-t6zw

Abstract

We study the galaxy bispectrum multipoles in the Hu-Sawicki gravity model, where a scalar degree of freedom mediates a fifth force that is screened in high-density environments. The model is specified by , the present-day background value of the scalar field, which controls the strength of deviations from General Relativity (GR). Using perturbation theory, we compute the redshift-space galaxy bispectrum with the full scale- and time-dependent second-order kernels, incorporating corrections from the scale-dependent growth rate and nonlinear screening. Expanding the bispectrum in spherical harmonics, we analyze the sensitivity of the multipoles to modified gravity and forecast their detectability in a \textit{Euclid}-like survey. The monopole () and quadrupole () show the strongest signatures, with relative deviations of -- at and (largest side of the triangle) for . Higher multipoles provide weaker but complementary signals. For \textit{Euclid}, we forecast signal-to-noise ratios up to for the monopole and for the quadrupole including the Finger-of-God damping and shot noise effect. These results demonstrate that bispectrum multipoles are a powerful probe of gravity, capable of breaking degeneracies with bias and velocity effects and strengthening constraints on deviations from CDM.

20 pages, 12 figures. Published in PRD

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