Orbifolds of M-Theory and Type II String Theories in Two Dimensions
  We consider several orbifold compactifications of M-theory and their corresponding type II duals in two space-time dimensions. In particular, we show that while the orbifold compactification of M-theory on $T^9/J_9$ is dual to the orbifold compactification of type IIB string theory on $T^8/I_8$, the same orbifold $T^8/I_8$ of type IIA string theory is dual to M-theory compactified on a smooth product manifold $K3 \times T^5$. Similarly, while the orbifold compactification of M-theory on $(K3 \times T^5)/\sigma ... J_5$ is dual to the orbifold compactification of type IIB string theory on $(K3 \times T^4)/\sigma ... I_4$, the same orbifold of type IIA string theory is dual to the orbifold $T^4 \times (K3 \times S^1)/\sigma ... J_1$ of M-theory. The spectrum of various orbifold compactifications of M-theory and type II string theories on both sides are compared giving evidence in favor of these duality conjectures. We also comment on a connection between Dasgupta-Mukhi-Witten conjecture and Dabholkar-Park-Sen conjecture for the six-dimensional orbifold models of type IIB string theory and M-theory. 
Shibaji Roy