Rationality of weighted hypersurfaces of special degree

Abstract

Let $X\subset \mathbb{P}(w_0,w_1,w_2,w_3)$ be a quasismooth well-formed weighted projective hypersurface and let $L=lcm(w_0,w_1,w_2,w_3)$. We characterize when $X$ is rational under the assumption that $L$ divides $deg(X)$ by combining an algebraic proof of rationality valid in all dimensions with a new result on numerical semigroups. As applications, we give new examples of families of normal projective rational varieties with quotient singularities and ample canonical divisor; we also determine precisely which affine Pham-Brieskorn threefolds are rational.

arXiv commentAdded 3.10 - 3.12. Other minor modifications