heavyN in the mass basis

Slightly modified version of: https://feynrules.irmp.ucl.ac.be/wiki/HeavyN

Adds vertices which were not originally present:

$$\mathcal{L}_Z = \frac{g}{2 \cos\theta_w} Z_\mu \bar{N}_i \gamma^\mu \left[\mathcal{C}_{ij} P_L - \mathcal{C}_{ij}^\ast P_R\right] N_j$$ $$\mathcal{L}_\phi = \frac{i g}{4 m_w} \phi^0 \bar{N}_i \left[\mathcal{C}_{ij} \left(m_j\,P_R - m_i\,P_L \right) + \mathcal{C}_{ij}^{\ast}\left(m_i P_R - m_j P_L\right)\right] N_j$$ $$\mathcal{L}_h = -\frac{g}{4 m_w} h \bar{N}_i \left[\mathcal{C}_{ij} \left(m_j\,P_R + m_i\,P_L \right) + \mathcal{C}_{ij}^{\ast}\left(m_i P_R + m_j P_L\right)\right] N_j$$

where

$$\mathcal{C}_{ij} = \sum_{\alpha} \Theta_{\alpha i}^\ast \Theta_{\alpha j}$$

at first order of the Seesaw expansion.