151 research outputs found
Phase structure of the QCD vacuum in a magnetic field at low temperature
We study the QCD phase structure in magnetic field at low temperature
. The hadronic phase free energy in a constant homogeneous magnetic field is
calculated in one-loop approximation of the chiral perturbation theory. The
dependence of the quark and gluon condensates upon the temperature and field
strength is found. It is shown that the chiral phase transition order parameter
remains constant provided field strength and temperature are
related via .Comment: LaTeX, 10 pages, 1 eps figure, replaced by version published in
Phys.Lett.
Confining strings and RG flow in the (2+1)-dimensional Georgi-Glashow model and its SU(3)-generalization
Confining strings and RG flow at finite temperature are investigated in the
(2+1)-dimensional Georgi-Glashow model. This is done in the limit when the
electric coupling constant is much larger than the square root of mass of the
Higgs field, but much smaller than the vacuum expectation value of this field.
The modification of the Debye mass of the dual photon with respect to the case
when it is considered to be negligibly small compared to the Higgs mass, is
found. Analogous modifications of the potential of monopole densities and
string coupling constants are found. At finite temperature, the mass of the
Higgs field scales according to a novel RG equation. It is checked that in the
limit when the original theory is reduced by the RG flow to the 2D XY model,
the so-evolved Higgs mass is still much smaller than the squared electric
coupling constant. The SU(3)-theory of confining strings is also discussed
within the same approximations.Comment: 14 pages, LaTeX2e, no figures, to appear in JHE
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.Comment: 8 pages, 4 figures; to appear in JETP Lett.; v2: references adde
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
-interactions and thermal excitations of and mesons are
calculated.Comment: 10 pages, LaTeX2e. Talk given at 12th International Seminar on
High-Energy Physics (QUARKS 2002), Novgorod, Russia, 1-7 Jun 200
Quark-hadron phase transition in a magnetic field
Quark-hadron phase transition in QCD in the presence of magnetic field is
studied. It is shown that both the temperature of a phase transition and latent
heat decrease compared to the case of zero magnetic field. The phase diagram in
the plane temperature--magnetic field is presented. Critical point, T_\ast=104
MeV, \sqrt{eH_\ast}=600 MeV, for which the latent heat goes to zero, is found.Comment: 10 pages, 2 figures. v2: new discussion and references added; version
to appear in Phys.Lett.
Low temperature relation for the trace of the energy-momentum tensor in QCD with light 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. The physical
consequences of this relation are discussed.Comment: RevTeX, 4 pages, no figure
Higgs- and quark-inspired modifications of the finite-temperature properties of the Polyakov model
(2+1)-dimensional Georgi-Glashow model, else called the Polyakov model, is
explored at nonzero temperatures and in the regime when the Higgs boson is not
infinitely heavy. The finiteness of the Higgs-boson mass leads to the
appearance of the upper bound on the parameter of the weak-coupling
approximation, necessary to maintain the stochasticity of the Higgs vacuum. The
modification of the finite-temperature behavior of the model emerging due to
the introduction of massless quarks is also discussed.Comment: 4 pages, LaTeX2e, no figures, uses espcrc2.sty, submitted to Nucl.
Phys. B (Proc. Suppl.
Instanton IR stabilization in the nonperturbative confining 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. It
is shown that instanton size in QCD is of order of 0.25 fm. Comparison of
obtained instanton size distribution with lattice data is made.Comment: 10 pages, 4 figures; v2: minor corrections, to appear in JHE
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