Published online by Cambridge University Press: 10 July 2020
Building upon our earlier work with M. C. Hughes, we construct many new smooth structures on closed simply connected nonspin $4$ -manifolds with positive signature. We also provide numerical and asymptotic upper bounds on the function $\lambda (\sigma )$ that was defined in our earlier work.
The first author was partially supported by a Simons Research Fellowship and Collaboration Grant for Mathematicians from the Simons Foundation. The second author was partially supported by an NSERC discovery grant.