Speaker
Description
The growth of small-scale structures in dark matter is hard to
access with numerical, observational and conventional analytical methods.
However, information about initial conditions and the properties of dark matter are supposed to leave their footprints in these small scale structures.
I present analytical work, where we show with Kinetic Field Theory (KFT) that the dark matter density perturbation power spectrum of cosmic structures necessarily develop a $k^{-3}$ tail when the initial phase space distribution is a Gaussian random field and trajectories are straight as in the famous Zel'dovich approximation. This result is independent of the initial power spectrum and also holds when no UV cutoff is imposed on the initial power spectrum. The power law exponent of $-3$ is a consequence of the number of spatial dimensions. Our result implies that universal small-scale structures necessarily form even when they are absent initially. From the asymptotic expansion that we derive, we are able to deduce time, length and mass scales characteristic for small structures in dark matter. These scales potentially leave measurable imprints in observables related to the CMB or the era of reionization, giving hints to the primordial n_s and the temperature of dark matter.
Additionally, in the analytical framework of KFT, particle-particle interactions beyond the Zel'dovich approximation can be computed with a mean field approach. This non-linear power spectrum agrees within a few percent with numerical simulations. We show that in this mean field theory, the power spectrum also has an asymptotic $k^{-3}$ tail, proving the universality of cosmic structures.
