3.2.1. ALF spaces of cyclic type [02GZ]
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3.2.1. ALF spaces of cyclic type
We saw that gravitational instantons of type can be constructed from Dirac monopoles on with singularities via the Gibbons–Hawking ansatz. These are usually called multi-Taub–NUT metrics. The case is the Taub–NUT metric on and is with its flat metric. Minerbe [35, Theorem 0.2] has shown that every ALF space of cyclic type must be isometric to a multi-Taub–NUT metric.
From their explicit description one can easily compute basic information about cyclic ALF spaces: the fundamental group , the second Betti number , the Euler characteristic and the dimension of the moduli space of metrics:
Here we assume that the asymptotic length of the circle fibre is normalised to be so that does not include rescalings.