TSPT: Time - sliced perturbation theory for large scale structures

I will present a new perturbative approach for the description of cosmological structures in the mildly non-linear regime relevant at the distance scales from 10 to 100 Mpc. In this framework equal-time correlation functions of cosmological perturbations are calculated using an ensemble with time-dependent statistical weight. The scheme is free of unphysical infrared divergencies plaguing the traditional approaches and allows systematic resummation of large infrared contributions to all orders in perturbation theory. This greatly improves the description of the density power spectrum in the region of baryon acoustic oscillations. I will also mention future directions, which include infrared resummation of higher-point correlation functions and the renormalisation of the contributions coming from short-wavelength modes.