CosmoCoffee

I would just like to draw you attention to this tour de force paper, presenting the perturbation theory from a fresh perspective. Basically, instead of doing the standard PT theory by considering powers in \delta and \theta, they express the final amplitude of a mode [tex]\mathbf{k}[/tex] as a sum over vertices corresponding to coupling with [tex]\mathbf{k}_1[/tex] and [tex]\mathbf{k}-\mathbf{k}_1[/tex] at some time \eta'<\eta (now). Then they do some heavy butchery summing up these diagrams to get a much better behaved expansion than the standard PT. I am not an expert, but it sounds very promising to me. There is also a companion paper [astro-ph/0509419], but I haven't managed to get that far so far...