The Zeldovich approximation
  This year marks the 100th anniversary of the birth of Yakov Zel'dovich.
Amongst his many legacies is the Zel'dovich approximation for the growth of
large-scale structure, which remains one of the most successful and insightful
analytic models of structure formation. We use the Zel'dovich approximation to
compute the two-point function of the matter and biased tracers, and compare to
the results of N-body simulations and other Lagrangian perturbation theories.
We show that Lagrangian perturbation theories converge well and that the
Zel'dovich approximation provides a good fit to the N-body results except for
the quadrupole moment of the halo correlation function. We extend the
calculation of halo bias to 3rd order and also consider non-local biasing
schemes, none of which remove the discrepancy. We argue that a part of the
discrepancy owes to an incorrect prediction of inter-halo velocity
correlations. We use the Zel'dovich approximation to compute the ingredients of
the Gaussian streaming model and show that this hybrid method provides a good
fit to clustering of halos in redshift space down to scales of tens of Mpc.
