## A Kummer-type construction of self-dual 4-manifolds.(English)Zbl 0818.53034

First, the authors introduce the notion called Taubes invariant for smooth oriented compact 4-manifolds. It is defined to be the least integer $$n$$ such that, for a given 4-manifold $$M$$, the connected sum $$M\# n\mathbb{C}\mathbb{P}_ 2$$ admit a self-dual metric.
The existence of such a finite integer was proved by C. H. Taubes [J. Differ. Geom. 36, No. 1, 163-253 (1992)]; however, as the authors claim, its value is hardly calculable. In this paper, they prove that the Taubes invariant for $$M= \overline \mathbb{C}\mathbb{P}_ 2$$ is between 2 and 14.
Second, and as the main contribution of this paper, the authors show how to construct the generalized connected sum of two self-dual orbifolds. Their argument extends really to the case of reflection orbifolds with a self-dual metric, these are manifolds with an action of $$\mathbb{Z}_ 2$$ equipped with a global self-dual Riemannian metric. A notable example is the compactification of the Eguchi-Hanson manifold.
Following and modifying the argument in [S. Donaldson and R. Friedman, Nonlinearity 2, No. 2, 197-239 (1989; Zbl 0671.53029)] the authors show the existence of self-dual metrics on such a connected sum of reflection orbifolds satisfying certain cohomological conditions. Then, this is applied to a pair of a reflection orbifold and the compactified Eguchi-Hanson orbifold, thus concluding the estimate of the Taubes invariant of $$\overline \mathbb{C}\mathbb{P}_ 2$$. As another application, the authors give an explicit construction of the Ricci-flat Kähler metric on a $$K3$$ surface belonging to a certain class, which is to be compared with the general existence theorem by Calabi-Yau of such metrics on $$K3$$-surfaces.
Reviewer: T.Sasaki (Kobe)

### MSC:

 53C07 Special connections and metrics on vector bundles (Hermite-Einstein, Yang-Mills) 53C55 Global differential geometry of Hermitian and Kählerian manifolds 32L25 Twistor theory, double fibrations (complex-analytic aspects) 32S30 Deformations of complex singularities; vanishing cycles

### Keywords:

Taubes invariant; self-dual metric; reflection orbifolds

Zbl 0671.53029
Full Text:

### References:

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