Signatures of the Standard Model in the evolution of cosmological perturbations

Within the standard cosmological paradigm, dark matter density fluctuations slowly grow during the radiation-dominated epoch, leading them to inherit the nearly scale-invariant shape of the primordial power spectrum. While new physics can change this picture, for instance, self-interactions among neutrinos or self-interacting dark matter, we point out here that Standard Model physics can also break off the nearly scale-invariant shape typically assumed. Overall, phenomena such as the electroweak decoupling of neutrinos and the evolution of the effective number of relativistic degrees of freedom g_*(T) impact the evolution of cosmological perturbations and induce clustering suppression at very small scales.