  This study investigates the effects on the connected and disconnected
correlations for the scalar density that are induced by created monopoles and
instantons in the QCD vacuum. To reveal the effects, we add a monopole and
anti-monopole pair in the gauge field configurations in \textit{SU}(3) by
applying the monopole creation operator to the vacuum. We vary the magnetic
charges of the monopole and anti-monopole and increase the number of monopoles
and anti-monopoles in the configurations. The Dirac operator of overlap
fermions preserves the exact chiral symmetry in lattice gauge theory and exact
zero-modes exist in its spectrum. The eigenvalues and eigenvectors of the
overlap Dirac operator have been calculated using these configurations, and the
numbers of instantons and anti-instantons which are created by these additional
monopoles and anti-monopoles have been estimated from the numbers of
topological charges in our previous studies. In this study, we demonstrate the
preliminary results that instantons and monopoles influence the masses that are
evaluated from the connected and disconnected correlation functions for the
scalar density using low-lying eigenvalues and eigenvectors of the overlap
Dirac operator.
