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GR: Fachverband Gravitation und Relativitätstheorie

GR 9: Cosmology

GR 9.2: Talk

Thursday, September 2, 2021, 16:45–17:00, H9

The functional renormalisation group of dark matter gravitational dynamics — •Alaric Erschfeld and Stefan Flörchinger — Institut für Theoretische Physik Heidelberg

While standard cosmological perturbation theory is applicable for the description of cosmic structure formation on large scales, it fails to accurately describe the mildly non-linear regime. The functional renormalisation group of the effective action describing the gravitational dynamics of dark matter, naturally allows for non-perturbative approximation schemes, either by the use of underlying symmetries or via a truncation of the effective action theory space. We show that Galilean invariance of the system gives rise to a Ward identity which allows to solve the renormalisation group flow equations in the limit of small scales and is related to the so-called `sweeping effect'. Further, we study the flow of an ansatz similar to a derivative expansion of the effective action, which describes dark matter in an effective theory with local dynamics. We find attractive ultraviolet fixed point solutions for the relevant flow parameter, which naturally capture the sweeping effect observed in Eulerian response functions. Further, the full renormalisation group flow is solved for the density and velocity power spectra in the perfect pressureless fluid approximation.