Yang-Mills instantons in an asymptotically locally flat background: Taub-NUT vs. Taub-Bolt

We present arguments for the existence of a one-parameter family of self-dual Yang-Mills instantons in the background of Taub-NUT and Taub-Bolt spaces. These solutions are finite everywhere and generically carry a non-integer Pontryagin charge. The Taub-NUT space configurations can be considered as interpolating (when varying the NUT parameter) between the Prasad-Sommerfield and BPST instantons.publishe