An $S^3\times S^3$ bundle over $S^4$ and new supergravity solutions

Abstract

The metric of $S^7$ can be written as an $SU(2)$-instanton bundle over $S^4$. It is also possible to write it differently as an anti-instanton bundle. We use this observation to construct an instanton--anti-instanton, $SU(2)\times SU(2)$, bundle over $S^4$. We show that this 10d manifold admits two Einstein metrics. We then rewrite the metric to isolate two $U(1)$ directions of the fibre and dimensionally reduce along them to get an eight dimensional metric describing an $S^2\times S^2$ bundle over $S^4$. This metric allows a harmonic 4-form which we use to derive new supergravity solutions in eleven and ten dimensions as $AdS_3\times M_8$ and $AdS_2\times M_8$, respectively.