Confinement- Deconfinement Phase Transition and Fractional Instanton   Quarks in Dense Matter
  We present arguments suggesting that large size overlapping instantons are the driving mechanism of the confinement-deconfinement phase transition at nonzero chemical potential mu. The arguments are based on the picture that instantons at very large chemical potential in the weak coupling regime are localized configurations with finite size \rho\sim\mu^{-1}. At the same time, the same instantons at smaller chemical potential in the strong coupling regime are well represented by the so-called instanton-quarks with fractional topological charge 1/N_c. We estimate the critical chemical potential mu_c(T) where transition between these two regimes takes place. We identify this transition with confinement- deconfinement phase transition.   We also argue that the instanton quarks carry magnetic charges. As a consequence of it, there is a relation between our picture and the standard t'Hooft and Mandelstam picture of the confinement. We also comment on possible relations of instanton-quarks with "periodic instantons", " center vortices", and "fractional instantons" in the brane construction. We also argue that the variation of the external parameter mu, which plays the role of the vacuum expectation value of a "Higgs" field at mu >> \Lambda_{QCD}, allows to study the transition from a "Higgs -like" gauge theory (weak coupling regime, mu>> \Lambda_{QCD}) to ordinary QCD (strong coupling regime, mu<< \Lambda_{QCD}). We also comment on some recent lattice results on topological charge density distribution which support our picture. 
Ariel R. Zhitnitsky