Additive actions on hyperquadrics of corank two

<abstract><p>For a projective variety $ X $ in $ {\mathbb{P}}^{m} $ of dimension $ n $, an additive action on $ X $ is an effective action of $ {\mathbb{G}}_{a}^{n} $ on $ {\mathbb{P}}^{m} $ such that $ X $ is $ {\mathbb{G}}_{a}^{n} $-invariant and the induced action on $ X $ has an open orbit. Arzhantsev and Popovskiy have classified additive actions on hyperquadrics of corank 0 or 1. In this paper, we give the classification of additive actions on hyperquadrics of corank 2 whose singularities are not fixed by the $ {\mathbb{G}}_{a}^{n} $-action.</p></abstract>