Equation Icon  (∂2t + ˆH2)φopt = 0 ,Hˆ2 = − Δopt + 𝒱 , ( 2 ) 𝒱 = e− 2σ (ξR + m2 ) − (d-−-2)-∇2σ − (d −-2)-(∇σ )2 , (191 ) 2 4