The dark matter bispectrum from effective viscosity and one-particle irreducible vertices

Understand

Dark matter evolution during the process of cosmological structure formation can be described in terms of a one-particle irreducible effective action at a characteristic scale $k_m$ and a loop expansion below this scale, based on the effective propagators and vertices.

• We calculate the form of the effective vertices and compute the bispectrum of density perturbations within a one-loop approximation.
• We find that the effective vertices play a subdominant role as compared to the effective viscosity and sound velocity that modify the (inverse) propagators.
• For the bispectrum we reproduce the results of standard perturbation theory in the range where it is applicable, and find a slightly improved agreement with N-body simulations at larger wavenumbers.