A New bound on CP Violation in the $τ$ Lepton Yukawa Coupling and electroweak baryogenesis

Abstract

CP violation in the third generation fermion Higgs couplings may play an important role in the electroweak baryogenesis, however it is strongly bounded by the experimental limits on the electron electric dipole moment. In the effective field theory framework to beyond the Standard Model physics, it can originate from dimension six operators. Under such assumptions like Minimal Flavour Violation or flavour symmetries, the Wilson coefficients of those operators have in general certain flavour structure. In that case the imaginary parts of the hτ τ and hee couplings are linked to each other. We point out that due to the very strong bound from the electron electric dipole moment on the imaginary part of hee coupling, the bound on the imaginary part of the hτ τ coupling is then generically two orders of magnitude stronger than the one obtained from the τ -loop contributions to the Barr-Zee diagram. We briefly discuss the potential impact of this fact on the electroweak baryogenesis.

Searching for BSM Physics in Yukawa Couplings and Flavour Symmetries

“…As reported in Ref. [24], once the presence of an underlying flavour symmetry is assumed, the bound in Eq. (3.3) can be translated into one on |κ τ |:…”

“…Within the same framework, it has recently been shown [24] that the bounds from the electron EDM on CP violation in the electron Yukawa coupling can be translated into bounds on CP violation in tau Yukawa coupling that are two orders of magnitude stronger than if no flavour symmetry is considered, with strong implications for the electroweak baryogenesis. The idea of linking the diagonal to off-diagonal Higgs-quark couplings with the purpose of constraining the diagonal light generation Yukawas by the tree-level contribution of the off-diagonal ones to the K, B and D meson oscillations has been proposed in Ref.…”

Dynamical Minimal Flavour Violating Inverse Seesaw

“…In an effective field theory approach, the Wilson coefficients of higher dimensional operators are made invariant under the flavour symmetry by inserting powers of the spurions, providing suppressions in terms of fermion masses and mixing. 1 The result is that, while the bounds on the NP scale in the absence of any flavour symmetry would be of hundreds of TeVs [19,20], in the M(L)FV case the NP scale can be at the TeV scale as proven in several contexts [8][9][10][11][12][13][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Despite this success, M(L)FV is not a flavour model, as masses and mixing can only be described and not predicted: in other words, the background values of the spurions are simply assumed as working hypotheses.…”