Nonexistence of twists and surgeries generating exotic 4-manifolds
  It is well known that for any exotic pair of simply connected closed oriented 4-manifolds, one is obtained from the other by twisting a compact contractible submanifold via an involution on the boundary. By contrast, here we show that for each positive integer $n$, there exists a simply connected closed oriented 4-manifold $X$ such that, for any compact (not necessarily connected) codimension zero submanifold $W$ with $b_1(\partial W)<n$, the set of all smooth structures on $X$ cannot be generated from $X$ by twisting $W$ and varying the gluing map. As a corollary, we show that there exists no `universal' compact 4-manifold $W$ such that, for any simply connected closed 4-manifold $X$, the set of all smooth structures on $X$ is generated from a 4-manifold by twisting a fixed embedded copy of $W$ and varying the gluing map. Moreover, we give similar results for surgeries. 
Kouichi Yasui
math.GT math.SG