An adjunction inequality for Real embedded surfaces

TL;DR

This paper establishes an adjunction inequality for Real embedded surfaces in 4-manifolds with involutions, linking cohomology classes, equivariant cohomology, and Seiberg--Witten invariants to the genus of such surfaces.

Contribution

It introduces a criterion for representing cohomology classes by Real surfaces and proves two versions of an adjunction inequality based on Seiberg--Witten invariants.

Findings

Real surfaces correspond to classes in equivariant cohomology.

Non-zero Real Seiberg--Witten invariants imply genus bounds.

Minimal genus of Real surfaces can exceed that of arbitrary surfaces.

Abstract

A Real structure on a $4$-manifold $X$ is an orientation preserving smooth involution $\sigma$. We say that an embedded surface $\Sigma \subset X$ is Real if $\sigma$ maps $\Sigma$ to itself orientation reversingly. We prove that a cohomology class $u \in H^2(X ; \mathbb{Z})$ can be represented by a Real embedded surface if and only if $u$ can be lifted to a class in equivariant cohomology $H^2_{\mathbb{Z}_2}(X ; \mathbb{Z}_-)$. We prove that if the Real Seiberg--Witten invariants of $X$ are non-zero then the genus of Real embedded surfaces in $X$ satisfy an adjunction inequality. We prove two versions of the adjunction inequality, one for non-negative self-intersection and one for arbitrary self-intersection. We show with examples that the minimal genus of Real embedded surfaces can be larger than the minimal genus of arbitrary embedded surfaces.