$\eta_c$ - glueball Mixing and Resonance X(1835)
  The mixing of $\eta_c$ and the lowest mass pseudoscalar glueball is estimated within the framework of the instanton liquid model. It is demonstrated that the mixing is large and may explain the difference between the observed mass of the glueball candidate X(1835) and the theoretical prediction of QCD sum rule analysis. 
Nikolai Kochelev, Dong-Pil Min