Cosmological constraints from harmonic space analysis of DES Y3 3x2 clustering

The large-scale distribution of matter, as mapped by photometric surveys like the Dark Energy Survey (DES), serves as a powerful probe into cosmology. It is especially sensitive to both the amplitude of mass fluctuation ($\sigma_8$) and the total matter density ($\Omega_m$). The fiducial analysis of 2-point clustering statistics of these surveys is invariably done in configuration space where complex masking scheme is easier to handle. However, such an analysis inherently mixes different scales together, requiring special care in modeling. In this study, we present an analysis of DES Y3 3x2 clustering data in harmonic space where small and large scales are better separated and can be neatly modeled using perturbative techniques. Using conservative scale cuts and a comprehensive treatment for astrophysical effects, we model the clustering data under a linear bias model for galaxies as well as under a third-order biasing prescription. For our fiducial analysis, we get $S_8 \equiv \sigma_8 \sqrt{\Omega_m/0.3} = 0.789\pm0.020$, consistent with the configuration space analysis presented by the DES collaboration, although with a preference for slightly lower $\Omega_m$ and a higher $\sigma_8$. The analysis sets the stage for a future search for signatures of primordial non-Gaussianity and blue-tilted isocurvature perturbations from photometric surveys.