2026/03/12 by Sankarshana Srinivasan, Shreya Prabhu, Kai Lehman +3
Physics and Astronomy · #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #Astronomy and Astrophysical Research
paper · pdf · doi:10.1088/1475-7516/2026/07/058
Abstract As cosmology rapidly approaches the data-dominated phase of stage IV large scale structure surveys, the modelling of nonlinear scales has become a serious challenge that faces the community, particularly when analysing models beyond w CDM. In this work, we emulate the matter power spectrum in a phenomenological parameterisation of modified gravity in which a time-varying effective gravitational constant μ and a gravitational slip η are binned in redshift. We are able to achieve accuracy < 1% in the modified gravity boost relative to COLA (COmoving Lagrangian Acceleration) simulations, up to k = 1 h Mpc -1 . The emulator is publicly available at https://github.com/sankarshana16/mgbinnedboostemulator . We forecast the constraining power for each bin using a simulated 3 × 2pt LSST Y10-like data vector and a 6 × 2pt LSST Y10 x Simons Observatory cosmic microwave background (CMB) lensing data vector. We recover the characteristic degeneracy between μ and η previously identified in Fisher forecasts and demonstrate that the best-constrained direction corresponds to the combination Σ = μ (1 + η )/2 which governs the lensing potential. We show that while large scale structure is sensitive to growth of structure at low redshift, CMB lensing extends the sensitivity to a higher redshift range. These results demonstrate that fast emulation of nonlinear modified-gravity effects enables full Bayesian analyses of model-agnostic gravity parameterisations with realistic survey data vectors and astrophysical systematics.