Study of properties of two color QCD at nonzero baryon density within lattice simulation

QCD properties at zero baryon density are well studied due to the method of lattice simulation. Unfortunately, lattice simulation cannot be applied for QCD at nonzero baryon density due to the sign problem. For this reason, we have poor knowledge about QCD properties at nonzero baryon density. The approach that allows one to study the properties of QCD at nonzero density is lattice simulation of theories which are free from sign problem. In this report we present the results of lattice simulation of such a theory - two color QCD at nonzero baryon density. Calculations were carried out at zero temperature and with two flavors of dynamic quarks. In our study we found several phases of dense two color QCD: the hadronic phase at small chemical potential ($\mu_q$); the phase of Bose-Einstein condensation of scalar diquarks at intermediate values of $\mu_q$; the phase with condensation quark Cooper pairs at large $\mu_q$. At ultrahigh densities ($\mu_q \sim 1000 MeV$) we found confinement/deconfinement transition which manifests itself in rising of the Polyakov loop and vanishing of the string tension. After the deconfinement is achieved at $\mu_q>1000 MeV$, we observe a monotonous decrease of the spatial string tension which ends up with vanishing at $\mu_q>2000 MeV$. From this observation we draw the conclusion that the confinement/deconfinement transition at finite density and zero temperature is quite different from that at finite temperature and zero density. Our results indicate that in very dense matter the quark-gluon plasma is in essence a weakly interacting gas of quarks and gluons without a magnetic screening mass in the system, sharply different from a quark-gluon plasma at large temperature.