HET seminar

Abstract: The two Higgs doublet model (2HDM) with natural flavour conservation and a real scalar potential (for CP conservation) is a very popular phenomenological and experimental benchmark model. A couple of years ago Fontes et al. pointed out that there is no evident reason why the CP violation within the CKM matrix should not "leak" into the scalar potential through divergent radiative corrections, thereby rendering the real 2HDM theoretically inconsistent. Unexpectedly, however, their direct calculation of the most divergent piece of the 3-loop tadpole for the pseudoscalar yielded zero. We consider this issue working in the unbroken phase of the real 2HDM with natural flavour conservation. We identify two necessary ingredients for such a radiative leak, and show that they first appear together only at 6-loop order in the unbroken phase. Surprisingly though, we are able to show through a diagrammatic argument that the most divergent piece of the imaginary part of the relevant diagrams also winds up vanishing at 6 loops. Along the way we point out through simple symmetry arguments that the version of the 2HDM in which natural flavour conservation is implemented using a softly-broken U(1) Peccei-Quinn-type symmetry (in place of the usual Z_2) is guaranteed to be safe from leaks of CP violation.