Knots that are not slice either in positons or in negatons

An oriented compact 4-manifold $V$ with boundary $S^3$ is called a positon (resp. negaton) if its intersection form is positive definite (resp. negative definite) and it is simply connected. In this paper, we prove that there exist infinitely many knots which cannot bound null-homologous disks either in positons or in negatons. As a consequence, we find knots that cannot be unknotted either by only positive crossing changes or by only negative crossing changes.