M-theory backgrounds with torus actions and brane--anti-brane systems.

Abstract

Given an M-theory background, a reduction along the orbits of an isometric circle action must be performed in order to retrieve Type IIA String Theory. We study M-theory backgrounds with isometric torus actions. In this case, the choice of a reduction circle is highly non-unique. However, different reduction circles give rise to dual Type IIA backgrounds. We consider actions on eleven dimensional backgrounds, allowing for possible fixed points of codimension four. The latter are interpreted as D6-branes and D6-anti-branes. We then use the torus action to conclude the existence of special reduction circles that lead to Type IIA on a manifold with boundary. We demonstrate this phenomenon explicitly for two special backgrounds and we examine some key aspects of their structure.