Resolving symplectic orbifolds with applications to finite group actions

Abstract

We associate to each symplectic $4$-orbifold $X$ a canonical smooth symplectic resolution $\pi :\tilde{X}\to X$, which can be done equivariantly if $X$ comes with a symplectic $G$-action by a finite group. Moreover, we show that the resolutions of the symplectic $4$-orbifolds $X/G$ and $\tilde{X}/G$ are in the same symplectic birational equivalence class; in fact, the resolution of $\tilde{X}/G$ can be reduced to that of $X/G$ by successively blowing down symplectic $(-1)$-spheres. To any finite symplectic $G$-action on a $4$-manifold $M$, we associate a pair $(M_G,D)$, where $\pi :M_G\to M/G$ is the canonical resolution of the quotient orbifold and $D$ is the pre-image of the singular set of $M/G$ under $\pi$. We propose to study the group action on $M$ by analyzing the smooth or symplectic topology of $M_G$ as well as the embedding of $D$ in $M_G$. In this paper, an investigation on the symplectic Kodaira dimension ${\kappa }^s$ of $M_G$ is initiated. In particular, we conjecture that ${\kappa }^s(M_G)\le {\kappa }^s(M)$. The inequality is verified for several classes of symplectic $G$-actions, including any actions on a rational surface or a symplectic $4$-manifold with ${\kappa }^s=0$.

39 pages, published. Error in the earlier version corrected here

References in corpus (8)

• Seiberg--Witten invariants and surface singularities
• Symmetric symplectic homotopy K3 surfaces
• Non-symplectic involutions of a K3 surface
• On the orders of periodic diffeomorphisms of 4-manifolds
• $G$-minimality and invariant negative spheres in $G$-Hirzebruch surfaces
• Desingularisation of orbifolds obtained from symplectic reduction at generic coadjoint orbits
• Homology Smale-Barden manifolds with K-contact and Sasakian structures
• Symplectic rational $G$-surfaces and equivariant symplectic cones

Cited by in corpus (4)

• Proper Orbifold Cohomology
• On a class of symplectic $4$-orbifolds with vanishing canonical class
• Resolution of $4$-dimensional symplectic orbifolds
• Finite group actions on symplectic Calabi-Yau $4$-manifolds with $b_1>0$