Theoretical Tools for Large Scale Structure.pdf

a r X i v : a s t r o - p h / 9 8 1 0 0 9 3 v 1 6 O c t 1 9 9 8 Theoretical Tools for Large Scale Structure J. Richard Bond1, Lev Kofman1, Dmitry Pogosyan1 and James Wadsley1,2 1 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George St., Toronto, ON M5S 3H8, Canada 2Astronomy Department, Univ. of Washington, Box 351580, Seattle WA 98195-1580 Abstract. We review the main theoretical aspects of the structure formation paradigm which impinge upon wide angle surveys: the early universe generation of gravitational metric fluctuations from quantum noise in scalar inflaton fields; the well understood and computed linear regime of CMB anisotropy and large scale structure (LSS) generation; the weakly nonlinear regime, where higher order per- turbation theory works well, and where the cosmic web picture operates, describing an interconnected LSS of clusters bridged by filaments, with membranes as the in- trafilament webbing. Current CMB+LSS data favour the simplest inflation-based ΛCDM models, with a primordial spectral index within about 5% of scale invariant and ?Λ ≈ 2/3, similar to that inferred from SNIa observations, and with open CDM models strongly disfavoured. The attack on the nonlinear regime with a variety of N-body and gas codes is described, as are the excursion set and peak-patch semi- analytic approaches to object collapse. The ingredients are mixed together in an illustrative gasdynamical simulation of dense supercluster formation. 1 Introduction By their very nature, wide angle surveys, whether of CMB anisotropies or galaxy redshifts, are designed to probe long wavelengths in the universe, i.e., low comoving Fourier wavenumbers k (Fig. 1). We are hoping for simplicity of interpretation, best if the observables are probes of linear physics, harder to disentangle if the probe is of the dissipative chaotic physics characterizing the highly nonlinear regime, and hopefully tractable in the mildly nonlinear regime. The goal is t