The lift of type IIA supergravity with D6 sources: M-theory with torsion

This paper is concerned with an extension of the well known Kaluza-Klein mechanism. As the standard ansatz for Kaluza-Klein reduction implies the existence of a gauge potential associated with the KK field strength, it follows immediately that this field strength satisfies its Bianchi identity. Hence, the standard KK formalism breaks down in the presence of a violated Bianchi identity. This occurs for example in the context of D6 sources. We will investigate and partially solve this problem in the context of the type IIA/M-theory duality. Our discussion is motivated by the construction of gauge/string duals with backreacting flavor branes using D6-branes, which appear in M-theory as KK-monopoles. We are able to derive source-modified equations of motion for the eleven-dimensional theory, and are subsequently able to obtain the source-modified type IIA equations by direct dimensional reduction.