Self-consistency of the Excursion Set Approach

Understand

The excursion set approach provides a framework for predicting how the abundance of dark matter halos depends on the initial conditions.

• A key ingredient of this formalism comes from the physics of halo formation: the specification of a critical overdensity threshold (barrier) which protohalos must exceed if they are to form bound virialized halos at a later time.
• Another ingredient is statistical, as it requires the specification of the appropriate statistical ensemble over which to average when making predictions.
• The excursion set approach explicitly averages over all initial positions, thus implicitly assuming that the appropriate ensemble is that associated with randomly chosen positions in space, rather than special positions such as peaks of the initial density field.