Quotient singularities, eta invariants, and self-dual metrics (Q309045)

The paper under review focuses on questions arising from the study of four-dimensional spaces that have isolated singularities or noncompact ends which are modeled, respectively, on neighbourhoods of the origin and of infinity of \(\mathbb{R}^4\setminus\Gamma,\) where \(\Gamma\subset \mathrm{SO}(4)\) is a finite subgroup which acts freely on \(S^3.\) In particular: NEWLINE{\parindent=0.6cmNEWLINE\begin{itemize}\item[--] A formula for the \(\eta\)-invariant of the signature complex for any finite subgroup of \(\mathrm{SO}(4)\) acting freely on \(S^3\) is given. An application of this is a nonexistence result for Ricci-flat ALE metrics on certain spaces. NEWLINE\item[--] A formula for the orbifold correction term that arises in the index of the self-dual deformation complex is proved for all finite subgroups of \(\mathrm{SO}(4)\) which act freely on \(S^3.\) Some applications of this formula to the realm of self-dual and scalar-flat Kähler metrics are also discussed. NEWLINE\item[--] Two infinite families of scalar-flat anti-self-dual ALE spaces with groups at infinity not contained in \(\mathrm{U}(2)\) are constructed. Using these spaces, examples of self-dual metrics on \(n\#\mathbb{CP}^2\) are obtained for \(n\geq 3\). These examples admit an \(S^1\)-action, but are not of LeBrun type. NEWLINENEWLINE\end{itemize}}