Symplectic actions of groups of order 4 on K3$^{[2]}$-type manifolds, and standard involutions on Nikulin-type orbifolds

Abstract: Given a K3^[2]-type manifold X with a symplectic involution i, the quotient X/i admits a Nikulin orbifold Y as terminalization. We study the symplectic action on X of a group G of order 4 that contains i, and the natural involution induced on Y (the two groups give two different results). We classify the irreducible components of the moduli space of X and Y in the projective case, giving some explicit examples. We give lattice-theoretic criteria that a Nikulin-type orbifold N has to satisfy to admit a symplectic involution that deforms to an induced one.