Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-09-24
A&A (2002), 382, 477
Astronomy and Astrophysics
Astrophysics
11 pages, final version published in A&A
Scientific paper
10.1051/0004-6361:20011584
We investigate the properties of the standard perturbative expansions which describe the early stages of the dynamics of gravitational clustering. We show that for hierarchical scenarios with no small-scale cutoff perturbation theory always breaks down beyond a finite order $q_+$. Besides, the degree of divergence increases with the order of the perturbative terms so that renormalization procedures cannot be applied. Nevertheless, we explain that despite the divergence of these subleading terms the results of perturbation theory are correct at leading order because they can be recovered through a steepest-descent method which does not use such perturbative expansions. Finally, we investigate the simpler cases of the Zel'dovich and Burgers dynamics. In particular, we show that the standard Burgers equation exhibits similar properties. This analogy suggests that the results of the standard perturbative expansions are valid up to the order $q_+$ (i.e. until they are finite). Moreover, the first ``non-regular'' term of a large-scale expansion of the two-point correlation function should be of the form $R^{-2} \sigma^2(R)$. At higher orders the large-scale expansion should no longer be over powers of $\sigma^2$ but over a different combination of powers of 1/R. However, its calculation requires new non-perturbative methods.
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