M theory on (K3×S¹)/Z₂

Abstract

We analyze M theory compactified on (K3×S¹)/Z₂ where the Z₂ changes the sign of the three-form gauge field, acts on S¹ as a parity transformation, and on K3 as an involution with eight fixed points preserving SU(2) holonomy. At a generic point in the moduli space the resulting theory has as its low-energy limit N=1 supergravity theory in six dimensions with eight vector, nine tensor, and 20 hypermultiplets. The gauge symmetry can be enhanced (e.g., to E₈) at special points in the moduli space. At other special points in the moduli space tensionless strings appear in the theory.