\alpha_- = k_{\textrm{AB}} - k_{\textrm{BA}} \\
\zeta = 2 \Delta \omega \, \alpha_- = h_1\\
\h_2 = \Psi = (p_B k_{\textrm{EX}} - p_A k_{\textrm{EX}})^2 + 4 p_A p_B k_{\textrm{ex}}^2 - \Delta \omega^2 \\
\phantom{\Psi} = ( p_A k_{\textrm{EX}} + p_B k_{\textrm{EX}} )^2 - \Delta \omega^2 \\
\phantom{\Psi} = k_{\textrm{ex}}^2 - \Delta \omega^2 \\