E6 symmetry breaking in the superstring theory

We derive two methods for determining the symmetry breaking of E₆ in the low energy superstring theory, and classify all breaking patterns. A method for calculating the effective Higgs vacuum expectation values is presented. We show that there are theories with naturally light SU₂^w Higgs doublets, and classify all theories in which this occurs. The phenomenology of spontaneously broken E₆ theories is discussed, emphasizing the issues of nucleon decay and neutrino masses.