21 | | The Zee-Babu model extends the Standard Model (SM) by two complex scalars, $k$ and $h$. |
22 | | Neither carries color or weak isospin but both are charged under weak hypercharge. |
23 | | $k$ and $h$ are assigned lepton number $L=+2$, which is normalized such that SM leptons carry $L=+1$. |
24 | | In terms of the SM Lagrangian $(\mathcal{L}_{\rm SM})$, the Lagrangian of the Zee-Babu model $(\mathcal{L}_{\rm ZB})$ is |
| 21 | The Zee-Babu model extends the Standard Model (SM) by two complex scalars, {{{k--}}} and {{{h-}}}. |
| 22 | Neither carries color or weak isospin but both are charged under weak hypercharge. {{{k--}}} and {{{h-}}} carry the electric charges {{{Q_k=-2}}} and {{{Q_h=-1}}}, respectively, and both are assigned lepton number {{{L=+2}}}. This is normalized such that SM leptons carry {{{L=+1}}}. |
| 23 | |
| 24 | In terms of the SM Lagrangian {{{L_SM}}}}, the Lagrangian of the Zee-Babu model {{{LZB}}} is |
96 | | |
97 | | |
98 | | Neutrino masses (mNk) and mixing parameters (Vlk) between heavy mass eigenstate and (active) flavor eigenstates are taken to be independent, phenomenological parameters. This allows for maximum flexibility and model independence when calculating rates. Therefore, some care is required by the user. |
99 | | The lepton number- and flavor-violating interactions of the Lagrangian allow for modeling of the Type I, Inverse, and Linear seesaw mechanisms at both lepton, hadron, and lepto-hadron colliders. |
| 98 | The parameter {{{mu}}} has mass dimension {{{GeV}}} and the {{{h-h-k}}} vertex violates lepton number conservation. |
| 99 | |
| 100 | Light neutrino masses are generated at two loops. They are described by {{{\delta\mathcal{L}_\nu}}}. |
| 101 | To phenomenologically parameterize the Lagrangian, neutrinos are assumed to be massless in the UFO. This allows all {{{f}}} and {{{g}}} to be taken independently from one another. |
| 102 | |
| 103 | '''Note''' that this model permits lepton flavor violation and lepton number violation. |
| 104 | |