$ M_R \gtrsim 10^{12}$ GeV, so that the simplest $(3,1)$ seesaw cannot even be considered a consistent effective theory. In contrast, in [[Standard Model ]{}]{}the quartic coupling $\lambda$ becomes negative at $\mathcal{O}(10^{10})$ GeV, so the instability problem can be avoided by embedding the theory in a larger one at or below this scale. Thus, the [[Standard Model ]{}]{}still provides a consistent effective description of physics at the electroweak scale while the (3,1) seesaw with $ M_R \gtrsim 10^{10}$ GeV cannot be considered even as a consistent effective theory.

-   As we will further elaborate, the instability problem only gets worse within higher (3,n) seesaw schemes, with $n \geq 2$, as the extra right-handed neutrinos contribute to the running and tend to further destabilize $\lambda$, as we discuss in the next Section, \[sec:3gen\].

Of course as the value of the Yukawa coupling $Y_\nu$ decreases, so does its impact on the RG running of $\lambda$. Also, for a given fixed value of the light neutrino mass $m_\nu$, say $0.1$ eV, the required mass of right-handed neutrinos $M_R$ will also decrease as the Yukawa coupling decreases. Combining these two effects we find that, for low enough $Y_\nu$, the $(3,1)$ type-I would still be 