Flavour and CP symmetries in the inverse seesaw

We consider an inverse seesaw mechanism of neutrino mass generation in which the Standard Model is extended by $3+3$ (heavy) sterile states, and endowed with a flavour symmetry $G_f$, $G_f=\Delta (3 \, n^2)$ or (6 n^2)$, CP symmetry. These symmetries are broken peculiar way, so that charged lepton sector residual $G_\ell$ preserved, while neutral fermion remains invariant under $G_\nu=Z_2 \times CP$. study concrete setup, where Majorana term for three states conserves $G_\nu$, remaining terms (i.e. couplings left-handed leptons heavy as well Dirac-type among latter) do not break perform comprehensive analysis mixing different classes symmetries, giving examples each these, detail impact additional on predictions mixing. further confront our results those obtained model-independent scenario, light matrix leaves $G_\nu$ intact. phenomenological particular concerning effects non-unitarity (which strongly constrain parameter space scenario), prospects neutrinoless double beta decay violating processes.