Hefty enhancement of cosmological constraints from the DES Y1 data using a Hybrid Effective Field Theory approach to galaxy bias

Abstract: We present a re-analysis of cosmic shear and galaxy clustering from first-year Dark Energy Survey data (DES Y1), making use of a Hybrid Effective Field Theory (HEFT) approach to model the galaxy-matter relation on weakly non-linear scales, initially proposed in Modi et al. (2020) (arXiv:1910.07097). This allows us to explore the enhancement in cosmological constraining power enabled by extending the galaxy clustering scale range typically used in projected large-scale structure analyses. Our analysis is based on a recomputed harmonic-space data vector and covariance matrix, carefully accounting for all sources of mode-coupling, non-Gaussianity and shot noise, which allows us to provide robust goodness-of-fit measures. We use the \textsc{AbacusSummit} suite of simulations to build an emulator for the HEFT model predictions. We find that this model can explain the galaxy clustering and shear data up to wavenumbers $k_{\rm max}\sim 0.6\, {\rm Mpc}^{-1}$. We constrain $(S_8,\Omega_m) = (0.786\pm 0.020,0.273^{+0.030}_{-0.036})$ at the fiducial $k_{\rm max}\sim 0.3\, {\rm Mpc}^{-1}$, improving to $(S_8,\Omega_m) = (0.786^{+0.015}{-0.018},0.266^{+0.024}{-0.027})$ at $k_{\rm max}\sim 0.5\, {\rm Mpc}^{-1}$. This represents a $\sim10\%$ and $\sim35\%$ improvement on the constraints derived respectively on both parameters using a linear bias relation on a reduced scale range ($k_{\rm max}\lesssim0.15\,{\rm Mpc}^{-1}$), in spite of the 15 additional parameters involved in the HEFT model. We investigate whether HEFT can be used to constrain the Hubble parameter and find $H_0= 70.7_{-3.5}^{+3.0}\,{\rm km}\,s^{-1}\,{\rm Mpc}^{-1}$. Our constraints are investigative and subject to certain caveats discussed in the text.