Flavor puzzle in three-Higgs-doublet models: Insights from Branco-Grimus-Lavoura and lessons from flavor data

Abstract

We study a variant of the three-Higgs-doublet model (3HDM), referred to as the Branco-Grimus-Lavoura–(BGL-)3HDM, incorporating a U(1)<inf>1</inf> × U(1)<inf>2</inf> symmetry, which can distinguish the primary sources of mass for different fermion generations. In the version considered here, the Yukawa matrices in the down-quark and charged lepton sectors are diagonal, thereby eliminating tree-level flavor changing neutral currents (FCNCs) in these sectors. FCNC interactions mediated by neutral nonstandard Higgses are confined to the up-quark sector only. No new Beyond-Standard-Model parameters are introduced by the Yukawa sector of the model, making it as economical as the natural flavor conservation (NFC) versions of 3HDM with a U(1)<inf>1</inf> × U(1)<inf>2</inf> symmetry in terms of the number of free parameters. However, even in the down-quark and in the charged lepton sectors, flavor diagonal but nonuniversal Higgs couplings set this model apart from the NFC versions of the 3HDM. © 2025 Elsevier B.V., All rights reserved.