Abstract:
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.
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