The flavor of a light charged Higgs

Abstract

The ATLAS Collaboration has recently reported a search for light-charged Higgs in t → H+b decay, with $$ {H}^{+}\to c\overline{b} $$ H + → c b ¯ . An excess with a local significance of approximately 3σ is found at $$ {m}_{H^{+}} $$ m H + ≈ 130 GeV, with a best-fit value of BR(t → H+b) × BR($$ {H}^{+}\to c\overline{b} $$ H + → c b ¯ ) = (1.6 ± 0.6) × 10−3. We study the implications of such a hypothetical signal in multi-Higgs doublet models. We take into account constraints from searches for other charged Higgs decays and from flavor-changing neutral current processes. Two Higgs doublet models with flavor structure dictated by natural flavor conservation (NFC), minimal flavor violation (MFV), or the Froggatt-Nielsen (FN) mechanism cannot account for such excess. A three-Higgs doublet model with NFC can account for the signal. The Yukawa couplings of the neutral pseudoscalar A in the down sector, $$ {\hat{Y}}_A^D $$ Y ̂ A D , should be larger by a factor of 4 – 6 compared to the corresponding Yukawa couplings of the Higgs h, $$ {\hat{Y}}_h^D $$ Y ̂ h D . We further present two minimal scenarios, one in which a single Yukawa coupling in the down sector, $$ {\left({\hat{Y}}_A^D\right)}_{bb} $$ Y ̂ A D bb , gives the only significant contribution, and one in which two Yukawa couplings in the up sector, $$ {\left({\hat{Y}}_A^U\right)}_{tt} $$ Y ̂ A U tt and $$ {\left({\hat{Y}}_A^U\right)}_{tc} $$ Y ̂ A U tc , give the only significant contributions, and we discuss possible tests of these scenarios.