Item

Abstract

Given integers $d\ge 3$ and $N\ge 3$. Let $G$ be a finite abelian group
acting faithfully and linearly on a smooth hypersurface of degree $d$ in the
complex projective space $\mathbb{P}^{N-1}$. Suppose $G\subset PGL(N,
\mathbb{C})$ can be lifted to a subgroup of $GL(N,\mathbb{C})$. Suppose
moreover that there exists an element $g$ in $G$ such that $G/\langle g\rangle$
has order coprime to $d-1$. Then all possible $G$ are determined (Theorem 4.3).
As an application, we derive (Theorem 4.8) all possible orders of linear
automorphisms of smooth hypersurfaces for any given $(d,N)$. In particular, we
show (Proposition 5.1) that the order of an automorphism of a smooth cubic
fourfold is a factor of 21, 30, 32, 33, 36 or 48, and each of those 6 numbers
is achieved by a unique (up to isomorphism) cubic fourfold.