Representing smooth 4-manifolds as loops in the pants complex

We show that every smooth, orientable, closed, connected 4 -manifold can be represented by a loop in the pants complex. We use this representation, together with the fact that the pants complex is simply connected, to provide an elementary proof that such 4-manifolds are smoothly cobordant to a connected sum of complex projective planes, with either orientation. We also use this association to give information about the structure of the pants complex. Namely, given a loop in the pants complex, L, which bounds a disk, D, we show that the signature of the 4-manifold associated to L gives a lower bound on the number of triangles in D.