type-I seesaw extensions of the Standard Model. In Section \[sec:maj\] we look at the Majoron extension of the canonical type-I seesaw. In addition to providing a viable dark matter candidate, we show how it helps stabilize the Higgs vacuum, which can be made stable all the way up to Planck scale. In Section \[sec:scoto\] we look at another simple extension of type-I seesaw, namely the recently proposed scoto-seesaw. We show that, apart from providing a WIMP dark matter candidate, this simple extension can also improve vacuum stability up to Planck scale. Finally, we conclude and summarize our main results in Section \[sec:summary-discussion\].

Higgs vacuum in the [[Standard Model ]{}]{} {#sec:sm-vac}
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Let’s start with briefly revisiting the status of the electroweak vacuum within the Standard Model. For a long time the Higgs boson was the “last” missing piece of the theory. The discovery of a scalar particle with mass $m_H \approx 125$ GeV at the Large Hadron Collider (LHC) is very suggestive that it could be the long-awaited [[Standard Model ]{}]{}Higgs boson. While further work is still needed to unambiguously establish this, current data so far indicates that its couplings and decay properties are close to the [[Standard Model ]{}]{}Higgs 