CP violation in H^\pm \to W^\pm Z: A physical approach for the 2HDM

Abstract

We investigate CP violation in the process H^\pm \to W^\pm Z within the framework of the two-Higgs-Doublet model (2HDM). Amplitudes are expressed transparently in terms of physical couplings. Our analysis qualitatively confirms recent results by Kanemura and Mura, for the interference between one-loop bosonic and fermionic amplitudes. Furthermore, we identify additional sources of CP violation arising from internal interference among the bosonic and also among the fermionic loop amplitudes. In the alignment limit, the asymmetry would vanish in the absence of fermionic loop contributions when the sum of the masses of the additional neutral scalars is higher than the mass of the Z. Our results allow for generic Yukawa couplings, and cover both explicit and spontaneous CP violation. For inclusive W^\pm and Z decays, the CP violation will only manifest itself as a charge asymmetry.

Figures (18)

• Figure 1: Left: circles with constant $e_2^2+e_3^2$; centre and right: charged-Higgs couplings $f_2$ and $f_3$. The phases of the $f_i$ are unphysical, the phases of $f_2$ and $f_3$ are shown with respect to that of $f_1$, which is taken real and positive. Three degrees of alignment, $\kappa$, are considered (see left panel): outer, middle and inner $e_2$-$e_3$ circles refer to $e_1=0.90v$, $e_1=0.95v$, and $e_1=0.99v$, respectively. The corresponding values of $f_1$ are also shown in the middle and right panel. The colours identify the quadrant in the complex $e_2$-$e_3$ plane of the left panel.
• Figure 2: Boson triangle diagrams involving the $q_i$ (or $q_j$) couplings.
• Figure 3: Other boson triangle diagrams. Some represent two cases, with a $W^\pm$ or a $G^\pm$.
• Figure 4: Boson loops---parts (B-1)--(B-4).
• Figure 5: Boson loops---parts (B-5)--(B-10).