Wavefunctionals/S-matrix techniques in de Sitter

Flat-space physics is highly constrained by basic principles such as Lorentz invariance, locality, unitarity and causality. This is neatly seen in the structure of scattering amplitudes. For processes occurring in an expanding background we do not have the same level of understanding, not even in the case of de Sitter space. In this talk I provide a brief account of some of the recent efforts which aim to fill this gap. I will discuss some novel results in the understanding of the analytic structure of the Bunch-Davies wavefunction(al) of the universe in the perturbative regime, some fundamental constraints that it ought to satisfy as well as some general insights coming from an underlying combinatorial structure.