Recently, the second author [18] constructed a simply connected symplectic 4-manifold with b C 2 D 1 and K 2 D 2 using a rational blow-down surgery, and then Y Lee and the second author [9] constructed a family of simply connected, minimal, complex surfaces of general type with p g D 0 and 1 Ä K 2 Ä 2 by modifying Park's symplectic 4-manifold. After this construction, it has been a natural question whether one can find a new family of surfaces of general type with p g D 0 and K 2 3 using the same technique.The aim of this article is to give an affirmative answer to this question. Precisely, we are able to construct a simply connected, minimal, complex surface of general type with p g D 0 and K 2 D 3 using a rational blow-down surgery and a Q-Gorenstein smoothing theory developed in Lee and Park [9]. The key ingredient for the construction of K 2 D 3 case is to find a rational surface Z which contains several disjoint chains of curves representing the resolution graphs of special quotient singularities. Once we have the right candidate Z for K 2 D 3, the remaining argument is parallel to that of the K 2 D 2 case which appeared in Lee and Park [9]. That is, we contract these chains of curves from the rational surface Z to produce a projective surface X with special quotient singularities. We then prove that the singular surface X has a Q-Gorenstein smoothing and the general fiber X t of the Q-Gorenstein smoothing is a simply connected minimal surface of general type with p g D 0 and K 2 D 3. The main result of this article is the following. Theorem 1.2 There exists a simply connected symplectic 4-manifold with b C 2 D 1 and K 2 D 4 which is homeomorphic, but not diffeomorphic, to a rational surfaceIt is a very intriguing question whether the symplectic 4-manifold constructed in Theorem 1.2 above admits a complex structure. One way to approach this problem is to use Q-Gorenstein smoothing theory as above. But since the cohomology H 2 .T 0 X / is not zero in this case, it is hard to determine whether there exists a Q-Gorenstein smoothing. Therefore we need to develop more Q-Gorenstein smoothing theory in order to investigate the existence of a complex structure on the symplectic 4-manifold constructed in Theorem 1.2. We leave this question for future research.
Q-Gorenstein smoothingIn this section we briefly review a theory of Q-Gorenstein smoothing for projective surfaces with special quotient singularities and we quote some basic facts developed in Lee and Park [9].Geometry & Topology, Volume 13 (2009)A simply connected surface of general type with p g D 0 and K 2 D 3 745