Identify the missing nonlinear correction in the redshift-space model

Determine whether the velocity-amplitude deficit in the hybrid redshift-space power-spectrum model is resolved by including the next order of the polynomial expansion in the redshift-space mapping or instead requires resumming that expansion.

Background

At twenty-five times the DESI survey volume, the hybrid model exhibits a substantial mismatch when tested against simulations. Rescaling the higher-order correction can bring the recovered velocity amplitude closer to the simulation input, but the pinned-cosmology fit remains statistically poor, indicating that the amplitude of the existing correction is not the sole missing ingredient.

The authors therefore leave unresolved the nature of the correction required beyond the current truncation. They specifically distinguish between adding the next expansion order and applying a resummation, making this an explicit model-development problem for the next emulator revision.