Matter power spectrum from a Lagrangian-space regularization of perturbation theory.

We present a new approach to computing the matter density power spectrum, from large linear scales to small, highly nonlinear scales. Instead of explicitly computing a partial series of high-order diagrams, as in perturbative resummation schemes, we embed the standard perturbation theory within a realistic nonlinear Lagrangian-space ansatz. We also point out that an "adhesion-like" regularization of the shell-crossing regime is more realistic than a "ZePdovich-like" behavior, where particles freely escape to infinity. This provides a "cosmic web" power spectrum with good small-scale properties that provide a good matching with a halo model on mildly nonlinear scales. We obtain a good agreement with numerical simulations on large scales, better than 3% for k ≤ 1h-1 Mpc--1, and on small scales, better than 10% for k 1h-1 Mpc-l, at z ≤ 0.35, which improves over previous methods. [ABSTRACT FROM AUTHOR]