φ φ = ( φ φ + φ φ 0 ) = 1 2 ( φ φ 1 + i φ φ 2 φ φ 3 + i φ φ 4 ) , where the superscripts + and 0 indicate the electric charge Q of the components. The weak hypercharge Y W of both components is 1. Before symmetry breaking, the Higgs Lagrangian is L H = ( D μ μ φ φ ) † † ( D μ μ φ φ ) − − V ( φ φ ) , where D μ μ is the electroweak gauge covariant derivative defined above and V ( φ φ ) is the potential of the Higgs field. The square of the covariant derivative leads to three and four point interactions between the electroweak gauge fields W μ μ a and B μ μ and the scalar field φ φ . The scalar potential is given by V ( φ φ ) = − − μ μ 2 φ φ † † φ φ + λ λ ( φ φ † † φ φ ) 2 , where μ μ 2 > 0 , so that φ φ acquires a non-zero Vacuum expectation value, which generates masses for the Electroweak gauge fields (the Higgs' mechanism), and λ λ > 0 , so that the potential is bounded from below. The quartic term describes self-interactions of the scalar field φ φ .