With a radio continuum galaxy survey by the Square Kilometre Array ( SKA ) , a photometric galaxy survey by Euclid and their combination , we forecast future constraints on primordial non-Gaussianity .
We focus on the potential impact of local-type higher-order nonlinear parameters on the parameter estimation and particularly the confirmation of the inflationary consistency inequality .
Nonstandard inflationary models , such as multifield models , introduce the scale-dependent stochastic clustering of galaxies on large scales , which is a unique probe of mechanism for generating primordial density fluctuations .
Our Fisher matrix analysis indicates that a deep and wide survey provided by SKA is more advantageous to constrain \tau _ { NL } , while Euclid has a strong constraining power for f _ { NL } due to the redshift information , suggesting that the joint analysis between them is quite essential to break the degeneracy between the nonlinear parameters .
The combination of the full SKA and Euclid will achieve the precision level needed to confirm the consistency inequality even for f _ { NL } \approx 1.5 and \tau _ { NL } \approx 17 , though it is still hard for a single survey to confirm it when f _ { NL } \lesssim 2.7 .