
CosmoCoffee

Authors:  M. Crocce, R. Scoccimarro 
Abstract:  We develop a new formalism to study nonlinear evolution in the growth of
largescale structure, by following the dynamics of gravitational clustering as
it builds up in time. This approach is conveniently represented by Feynman
diagrams constructed in terms of three objects: the initial conditions (e.g.
perturbation spectrum), the vertex (describing nonlinearities) and the
propagator (describing linear evolution). We show that loop corrections to the
linear power spectrum organize themselves into two classes of diagrams: one
corresponding to modecoupling effects, the other to a renormalization of the
propagator. Resummation of the latter gives rise to a quantity that measures
the memory of perturbations to initial conditions as a function of scale. As a
result of this, we show that a welldefined (renormalized) perturbation theory
follows, in the sense that each term in the remaining modecoupling series
dominates at some characteristic scale and is subdominant otherwise. This is
unlike standard perturbation theory, where different loop corrections can
become of the same magnitude in the nonlinear regime. In companion papers we
compare the resummation of the propagator with numerical simulations, and apply
these results to the calculation of the nonlinear power spectrum. Remarkably,
the expressions in renormalized perturbation theory can be written in a way
that closely resembles the halo model. 

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Anze Slosar
Joined: 24 Sep 2004 Posts: 205 Affiliation: Brookhaven National Laboratory

Posted: September 18 2005 


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 δ and θ, they express the final amplitude of a mode as a sum over vertices corresponding to coupling with and at some time η'<η (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 [astroph/0509419], but I haven't managed to get that far so far... 

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