Vacuum Structure and Chiral Charge Quantization in the Large N Limit

The chiral structure of the vacuum is analysed with the help of the effective U(1) Lagrangian. The origin of the vacuum angle θ is discussed in this large N approach. The angle θ is shown to be an angular variable with period 2π even if we include 1/N nonleading terms, although this periodicity disappears in the large N limit. It is argued that "topological charge" and chiral charges are quantized in integer and even integer units, respectively. The total space of states is also explicitly constructed with these charge eigenstates and the conventional Fock space.