With the above constraint Eqs.(7) on Ψ Ψ then p 2 Ψ Ψ = p ⊥ ⊥ 2 Ψ Ψ where p ⊥ ⊥ = p − − p ⋅ ⋅ P P / P 2 . This allows writing Eq. (9) in the form of an eigenvalue equation { p ⊥ ⊥ 2 + Φ Φ ( x ⊥ ⊥ ) } Ψ Ψ = b 2 ( w 2 , m 1 2 , m 2 2 ) Ψ Ψ ,