On the Pin(2)-equivariant monopole Floer homology of plumbed 3-manifolds

Abstract: We compute the Pin(2)-equivariant monopole Floer homology for the class of plumbed 3-manifolds with at most one "bad" vertex (in the sense of Ozsvath and Szabo). We show that for these manifolds, the Pin(2)-equivariant monopole Floer homology can be calculated in terms of the Heegaard Floer/monopole Floer lattice complex defined by Nemethi. Moreover, we prove that in such cases the ranks of the usual monopole Floer homology groups suffice to determine both the Manolescu correction terms and the Pin(2)-homology as an abelian group. As an application of this, we show that $\beta(-Y, s) = \bar{\mu}(Y, s)$ for all plumbed 3-manifolds with at most one bad vertex, proving a conjecture posed by Manolescu. Our proof also generalizes results by Stipsicz and Ue relating the Neumann-Siebenmann invariant with the Ozsvath-Szabo $d$-invariant.