THE BERNOULLI OPERATOR

ABSTRACT. This document explores the Bernoulli operator, giving it a variety of different definitions. In one definition, it is the shift operator acting on infinite strings of binary digits. In another definition, it is the transfer operator (the Frobenius-Perron operator) of the Bernoulli map, also variously known as the doubling map or the sawtooth map. The map is interesting for multiple reasons. One is that the set of infinite binary strings is the Cantor set; this implies that the Bernoulli operator has a set of fractal eigenfunctions. These are given by the Takagi (or Blancmange) curve. The set of all infinite binary strings can also be understood as the infinite binary tree. This binary tree has a large number of self-similarities, given by the dyadic monoid. The dyadic monoid has an extension to the modular group PSL(2,Z), which plays an important role in analytic number theory; and so there are many connections between the Bernoulli map and various number-theoretic functions, including the Moebius function and the Riemann zeta function. The Bernoulli map has been studied as a shift operator, in the context of functional analysis [24]. More recently, it has been studied in the physics community as an exactly solvable model for chaotic dynamics and the entropy-increaing thermodynamic arrow o