Effective Lagrangian at \(\mu = m_a = 2\,\mathrm{GeV}\): $$\mathcal{L}_\mathrm{eff} \supset \frac{\partial_\mu a}{f_a}\left(c_{sb}^V \bar{s} \gamma^\mu b + c_{sb}^A \bar{s}\gamma^\mu \gamma_5 {b}\right) +\mathrm{h.c}.$$
Flavour violation induced by top loops, \(c_{sb}^V = - c_{sb}^A\), is compatible with both \(B^+ \to K^+ \nu \bar{\nu}\) and \(B^+ \to K^{*+} \nu \bar{\nu}\) constraints.