We present an interpretable emulator for the linear matter power spectrum (MPS) in the standard cosmological model $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$), constructed via a physics-informed symbolic regression framework. By combining domain knowledge with a machine learning technique known as genetic algorithms (GA), we explore the space of analytic expressions to derive closed-form, smooth, physically motivated approximations of the MPS that match the accuracy of standard broadband reconstruction methodologies such as the Savitzky-Golay filter. Building upon this baseline, we incorporate transparent oscillatory corrections informed by the physics of baryon acoustic oscillations (BAO). The resulting expression delivers mean sub-percent fractional errors across a broad range of scales ($k\in [{10}^{-5},1.5]h{\mathrm{Mpc}}^{-1}$) with an average deviation of $\sim 0.4\%$ when tested against spectra computed with a Boltzmann solver. Moreover, a comparable level of fractional deviation is maintained on smaller scales when the GA-derived formulation is used as input to the nonlinear emulator halofit. To illustrate the versatility of the framework beyond $\mathrm{\Lambda }\mathrm{CDM}$, we apply it to a representative $f(R)$ gravity model. Rather than training a general modified-gravity (MG) emulator, we compute the corresponding linear spectra with a Boltzmann solver and fit a parametric deformation of the $\mathrm{\Lambda }\mathrm{CDM}$ smoothed component. This procedure achieves average errors at the 1.5–1.8% level and captures the leading modulation of the MPS induced by modified gravity, enabling a controlled study of its impact on the BAO scale. Our results provide compact, accurate, and physically motivated fitting functions for the linear MPS in both standard and MG cosmologies, offering a fast and transparent alternative to existing emulators for parameter inference and theoretical modeling in large-scale structure analyses.

Close

PrevNext

View figure in article

• Alternative gravity theories
• Cosmology
• Large scale structure of the Universe