arXiv subjects

Nikita O. Agasian

Publications and source records attributed to Nikita O. Agasian.

6 recordsLinked to original sources

arXiv2003

Hadron resonance gas and nonperturbative QCD vacuum at finite temperature

We study the nonperturbative QCD vacuum with two light quarks at finite temperature in the framework of hadron resonance gas. Temperature dependence of the quark and gluon condensates in the confined phase are obtained. We demonstrate that the quark condensate and one half (chromo-electric component) of gluon condensate evaporate at the same temperature, which corresponds to the temperature of quark-hadron phase transition. Critical temperature is T_c~190 MeV when temperature shift of hadron masses is taken into account.

hep-ph↗

arXiv2003

Thermal gluo-magnetic vacuum of SU(N) gauge theory

The magnetic sector of SU(N) Yang-Mills theory at finite temperature is studied. At low temperatures, T<2T_c, the analytic expressions for the temperature dependence of the magnetic correlator, of the magnetic gluon condensate and of the spatial string tension are obtained. Fair agreement with lattice calculations for spatial string tension is obtained for SU(2) and SU(3) gauge theories. The relative contribution given by non-zero Matsubara modes to the spatial string tension is calculated. At T=2T_c this contribution is of the order of 5%. The behavior of magnetic correlator at high temperatures is investigated and it is shown that gluo-magnetic condensate increases with temperature as (T)= const g^8(T) T^4.

hep-ph↗

arXiv2002

Low temperature relations in QCD

In this talk I discuss the low temperature relations for the trace of the energy-momentum tensor in QCD with two and three quarks. It is shown that the temperature derivatives of the anomalous and normal (quark massive term) contributions to the trace of the energy-momentum tensor in QCD are equal to each other in the low temperature region. Leading corrections connected with $ππ$-interactions and thermal excitations of $K$ and $η$ mesons are calculated.

hep-ph↗

arXiv2002

Instantons in the nonperturbative QCD vacuum

The influence of nonperturbative fields on instantons in quantum chromodynamics is studied. Nonperturbative vacuum is described in terms of nonlocal gauge invariant vacuum averages of gluon field strength.Effective action for instanton is derived in bilocal approximation and it is demonstrated that stochastic background gluon fields are responsible for infra-red (IR) stabilization of instantons. Dependence of characteristic instanton size on gluon condensate and correlation length in nonperturbative vacuum is found. Comparison of obtained instanton size distribution with lattice data is made.

hep-ph↗

arXiv2002

Finite Temperature Behavior of the 3D Polyakov Model with Massless Quarks

The (2+1)D Georgi-Glashow (or Polyakov) model with the additional fundamental massless quarks is explored at finite temperature. In the case of vanishing Yukawa coupling, it is demonstrated that the interaction of a monopole and an antimonopole in the molecule via quark zero modes leads to the decrease of the Berezinsky-Kosterlitz-Thouless critical temperature when the number of quark flavors is equal to one. If the number of flavors becomes larger, monopoles are shown to exist only in the molecular phase at any temperatures exceeding a certain exponentially small one. This means that for such a number of flavors and at such temperatures, no fundamental matter can be confined by means of the monopole mechanism.

hep-th↗

arXiv2001

Chiral thermodynamics in a magnetic field

We study thermodynamic properties of the QCD vacuum in a magnetic field below chiral phase transition. The hadronic phase free energy in a constant homogeneous magnetic field is calculated in the framework of the chiral perturbation theory at non-zero pionic mass. It is demonstrated that the order parameter of the chiral phase transition remains constant provided temperature and magnetic field strength are related through obtained equation (the phenomenon of ''quark condensate freezing'').

hep-ph↗