Upgrading and Downgrading Torus Actions

Abstract: K. Altmann and J. Hausen have shown that affine T-varieties can be described in terms of p-divisors. Given a p-divisor describing a T-variety X, we show how to construct new p-divisors describing X with respect to actions by larger tori. Conversely, if dim T=dim X-1, we show how to construct new p-divisors describing X with respect to actions by closed subtori of T. As a first application, we give explicit constructions for the p-divisors describing certain Cox rings. Furthermore, we show how to upgrade the p-divisors describing the total spaces of homogeneous deformations of toric varieties.