Abstract
The origin of the matter-antimatter asymmetry in the Universe is a fundamental question of physics. Electroweak baryogenesis is a compelling scenario for explaining it but it requires beyond the Standard Model sources of the CP symmetry violation. The simplest possibility is CP violation in the third generation fermion Higgs couplings, widely investigated theoretically and searched for experimentally. It has been found that the experimental bounds on the CP violation in the quark Yukawa couplings exclude their significant role in the electroweak baryogenesis, but it can be still played by the τ lepton Yukawa coupling. It is shown in this paper that, within the context of the Standard Model Effective Field Theory and assuming an underlying flavour symmetry of the Wilson coefficients, the electron dipole moment bound on the τ lepton Yukawa coupling is two orders of magnitude stronger than previously reported. This sheds strong doubts on its role in the electroweak baryogenesis, further stimulates the interest in its experimental verification and makes electroweak baryogenesis even more difficult to explain.
Highlights
The electron EDMWhere de is the EDM coefficient, e the electron field, σμν the antisymmetric two-dimensional tensor, and Fμν the electromagnetic gauge field tensor
Provided the first order phase transition is strong enough, the smallest value for κτ to entirely explain BAU, and being compatible with LHC Higgs signal strength at 2 σ, reads [7]
Electroweak baryogenesis is a compelling scenario for explaining it but it requires beyond the Standard Model sources of the CP symmetry violation
Summary
Where de is the EDM coefficient, e the electron field, σμν the antisymmetric two-dimensional tensor, and Fμν the electromagnetic gauge field tensor. In the leading order in new physics effects, the bound on κτ is obtained when the lepton τ is running in the loop and for κe = 0. We assume that the dominant contribution to the effective lepton Yukawa couplings, eq (1.1), comes from d = 4 and d = 6 operators of the SMEFT Lagrangian. We assume that the flavour structure of that Lagrangian is either compatible with the MFV hypothesis or controlled by a flavour symmetry that is responsible for the charged lepton masses. Where the matrix C is given in terms of the original Lagrangian parameters by the matrix equation in eq (2.12): Cii = Vk∗iCklUli. we discuss the significance of the bound in eq (2.16) for several concrete scenarios of the flavour structure of the SMEFT Yukawa Lagrangian
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