Matrix Formalism of Excursion Set Theory: A new approach to statistics
  of dark matter halo counting
  Excursion set theory (EST) is an analytical framework to study the
large-scale structure of the Universe. EST introduces a procedure to calculate
the number density of structures by relating the cosmological linear
perturbation theory to the nonlinear structures in late time. In this work, we
introduce a novel approach to reformulate the EST in matrix formalism. We
propose that the matrix representation of EST will facilitate the calculations
in this framework. The method is to discretize the two-dimensional plane of
variance and density contrast of EST, where the trajectories for each point in
the Universe lived there. The probability of having a density contrast in a
chosen variance is represented by a probability ket. Naturally, the concept of
the transition matrix pops up to define the trajectories. We also define the
probability transition rate which is used to obtain the first up-crossing of
trajectories and the number count of the structures. In this work we show that
the discretization let us study the non-Markov processes by forcing them to
look like a Wiener process. Also we discuss that the zero drift processes with
Gaussian and also non-Gaussian initial conditions can be studied by this
formalism. The continuous limit of the formalism is discussed, and the known
Fokker-Planck dispersion equation is recovered. Finally we show that the
probability of the most massive progenitors can be extracted in this framework.
