In multi-Higgs-doublet models the alignment in flavor space of the relevant Yukawa matrices guarantees the absence of tree-level flavor-changing couplings of the neutral scalar fields. We analyze the consequences of this condition within the two-Higgs-doublet model and show that it leads to a generic Yukawa structure which contains as particular cases all known specific implementations of the model based on ${\mathcal{Z}}_2$ symmetries. All possible freedom in the Yukawa sector gets parametrized in terms of three complex couplings ${\varsigma }_f$. In spite of having flavor conservation in the neutral scalar couplings, the phases of these three parameters represent potential new sources of $CP$ violation.

• Received 10 August 2009

DOI:https://doi.org/10.1103/PhysRevD.80.091702