Beschreibung
Inflation offers a compelling explanation of how the primordial universe evolved into the universe well described by $\Lambda$CDM. Measuring the non-Gaussianity of primordial density fluctuations will deliver crucial insight into the more fundamental mechanism behind inflation. We forecast future constraints on local primordial non-Gaussianity ($f_{\rm NL}^{\rm loc}$) under the context of LSST/SPHEREx$\times$SO. This leverages the $f_{\rm NL}$-induced scale dependent bias on galaxy overdensity $\delta_g$, cross-correlated with the CMB kinetic Sunyaev-Zeldovich (kSZ) reconstructed velocity $v$ for cosmic variance cancellation. The large-scale $gg$ autospectrum suffers from observational systematics, but we emphasize that removing large-scale $gg$-auto and relying solely on $gv$ cross correlations yields a promising $\sigma(f_{\rm NL})\sim 1$, where $\sigma(f_{\rm NL})$ is the error bar in measuring $f_{\rm NL}^{\rm loc}$. We also briefly discuss how this constraint depends on the uncertain kSZ velocity signal amplitude. Finally, we compare cross-correlations between $\delta_g\times\kappa$ (CMB lensing) and $\delta_g\times v$ for constraining $f_{\rm NL}^{\rm loc}$.