Researchers have investigated the quadratic-order effective energy-momentum tensor (2EMT) of scalar cosmological perturbations during slow-roll inflation. This tensor is constructed from terms quadratic in the linear metric and inflaton perturbations, making it a gauge-fixed effective source rather than a gauge-invariant observable. The study focuses on uniform-density hypersurfaces, imposing the complete scalar gauge conditions $\delta\rho=0$ and $E=0$, and expressing all perturbations in terms of the Bardeen potential $\Psi$. Calculations were performed in Fourier space for long- and short-wavelength domains, distinguishing between strict infrared and ultraviolet limits, and intermediate regimes.

Results show that in the strict infrared limit, uniform-density and comoving results agree. However, in the intermediate infrared regime, while the dominant leading order remains the same, explicit finite-gradient corrections distinguish the two gauges. In the ultraviolet, the 2EMT is enhanced by a factor of $1/\varepsilon$ due to the slowly varying matter clock ($\rho_0'\propto\varepsilon$). Furthermore, the leading uniform-density 2EMT terms exhibit an additional enhancement by $1/\sigma_2^2$ (where $\sigma_2\equiv \mathcal{H}/k$) from the Laplacian term. The intermediate ultraviolet expansion makes the subleading gradient hierarchy explicit without changing the leading terms.

Comparison with newly recalculated longitudinal, spatially-flat, and comoving expressions reveals a structured gauge dependence. Uniform-density and comoving slicings coincide for adiabatic super-Hubble modes, whereas the longitudinal and spatially-flat gauges are slow-roll suppressed in the strict infrared and become gradient-dominated in the intermediate infrared. This work provides a more detailed understanding of how different gauge choices affect the description of cosmological perturbations during inflation, a crucial period for the formation of the universe's structures.