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.Comment: Invited talk delivered at the Light Cone Workshop, July 7-15, 2005, Cairns, Australi

Topological Defects in QCD at large Baryon Density and/or large NcN_c

The main leitmotiv of the present talk is analysis of different topological objects such as strings and domain walls in QCD. As it is well known, the standard model in general (and QCD in particular) does not support any kind of such objects due to some simple topological arguments. However, the situation cardinally changes when one considers QCD in large $N_c$ limit or in the limit of large baryon density when the unique light $\eta'$ field emerges. I discuss $\eta'$- domain walls and $\eta'$ global strings which occur in both systems: in high density QCD and in QCD at large $N_c$. I also discuss the effects of quantum anomalies in the presence of topological objects in high-density QCD. The anomaly induced interactions lead to a number of interesting phenomena (such as the induced currents along the strings) which may have phenomenological consequences observable in neutron stars.Comment: Invited talk at the workshop "large N_c QCD", July, 5-9, 2004, Trento, to be published in the Proceeding