Perturbation Theory Trispectrum in the Time Renormalisation Approach
  An accurate theoretical description of structure formation at least in the mildly non-linear regime is essential for comparison with data from next generation galaxy surveys. In a recent approach one follows the time evolution of correlators directly and finds a hierarchy of evolution equations with increasing order (Pietroni 2008). So far, in this so called time renormalisation group method the trispectrum was neglected in order to obtain a closed set of equations. In this work we study the influence of the trispectrum on the evolution of the power spectrum. In order to keep the numerical cost at a manageable level we use the tree-level trispectrum from Eulerian perturbation theory. In comparison to numerical simulations we find improvement in the mildly non-linear regime up to k = 0.25 h/Mpc. Beyond k = 0.25 h/Mpc the perturbative description of the trispectrum fails and the method performs worse than without the trispectrum included. Our results reinforce the conceptual advantage of the time renormalisation group method with respect to perturbation theory. 
Gero J\"urgens and Matthias Bartelmann
astro-ph.CO