Note that the CP-conserving part of such terms is absorbed, by definition, into the quantity $P$. We will not attempt a theoretical calculation of this quantity (which is difficult even in the SM) and only consider observables that are independent of $P$. In the SM, $\rho\simeq\varepsilon_a\sin\gamma$ [@me] describes a small contribution induced by final-state rescattering from tree or annihilation diagrams [@Blok97; @BFM98; @Ge97; @Ne97; @Fa97; @At97]. In the heavy-quark limit, the parameter $\varepsilon_a$ can be calculated and is found to be of order $-2\%$ [@fact].

Finally, in the SM the parameter $b$ vanishes, while $$\label{delval}
   a\,e^{i\phi_a} = \delta_{\rm EW} 
   = (0.64\pm 0.09)\times\frac{0.085}{|V_{ub}/V_{cb}|}$$ is calculable in terms of fundamental parameters [@NR; @me; @Fl96]. Up to some small SU(3)-breaking corrections, $\delta_{\rm EW}$ is given by the Wilson coefficient $c_3^{\rm EW}(m_W)$ in (\[SMinit\]) divided by $-|\lambda_u|$. There are no additional hadronic uncertainties in this estimate in the SM. In particular, the strong-interaction phase $\phi_a$ is bounded to be less than a few degrees and can be neglected for all practical purposes [@me]. In a general model, the parameters $a$ and $b$ depend on the values of the penguin coefficients $c_i^{\rm EW}$ and $\widetilde c_i^{\rm EW}$ as well as on the hadronic matrix elements 