The symplectic structure of a toric conic transform

Abstract

Suppose that a compact $r$-dimensional torus $T^r$ acts in a holomorphic and Hamiltonian manner on polarized complex $d$-dimensional projective manifold $M$, with nowhere vanishing moment map $\Phi$. Assuming that $\Phi$ is transverse to the ray through a given weight $\mathbf{\nu }$, associated to these data there is a complex $(d-r+1)$-dimensional polarized projective orbifold ${\hat{M}}_{\mathbf{\nu }}$ (referred to as the $\mathbf{\nu }$-th \textit{conic transform} of $M$). Namely, ${\hat{M}}_{\mathbf{\nu }}$ is a suitable quotient of the inverse image of the ray in the unit circle bundle of the polarization of $M$. With the aim to clarify the geometric significance of this construction, we consider the special case where $M$ is toric, and show that ${\hat{M}}_{\mathbf{\nu }}$ is itself a Kähler toric obifold, whose moment polytope is obtained from the one of $M$ by a certain "transform", operation (depending on $\Phi$ and $\mathbf{\nu }$).