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 * = 104 MeV, √ eH * = 600 MeV, for which the latent heat goes to zero, is found.
The thermodynamics of a three-dimensional ͑3D͒ adjoint Higgs model is considered. We study the properties of the Polyakov loop correlators and the critical behavior at the deconfinement phase transition. Our main tool is a reduction to the 2D sine-Gordon model. The Polyakov loops appear to be connected with the soliton operators in it. The known exact results in the sine-Gordon theory allow us to study in detail the temperature dependence of the string tension, as well as to get some information about the nonperturbative dynamics in the confinement phase. We also consider symmetry restoration at high temperature which makes it possible to construct the phase diagram of the model completely. ͓S0556-2821͑98͒00802-9͔
The low-energy QCD theorems are generalized in the presence of a constant magnetic field H. Two-loop approximation for the vacuum energy density in the framework of the chiral perturbation theory was obtained and the quark and gluon condensates were found as the functions of H.
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.Comment: 12 pages, 3 figures; minor corrections, to appear in Phys.Lett.
In the first order of chiral perturbation theory the corrections to F π 0 and M π 0 in a magnetic field at finite temperature have been found. It was shown that they are shifted in such a manner that Gell-Mann -Oakes -Renner relation remains valid under these conditions.
The Debye mass m_D is computed nonperturbatively in the deconfined phase of
QCD, where chromomagnetic confinement is known to be present. The latter
defines m_D to be m_D=c_D\sqrt{\sigma_s}, where c_D \cong 2.06 and
\sigma_s=\sigma_s(T) is the spatial string tension. The resulting magnitude of
m_D(T) and temperature dependence are in good agreement with lattice
calculations. Background perturbation theory expansion for m_D(T) is discussed
in comparison to standard perturbative results and recent gauge-invariant
definitions.Comment: 14 pages, 4 figures; new figures and discussion added; to appear in
Phys.Lett.
We study the QCD phase structure in magnetic field H at low temperature T . 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 qq remains constant provided field strength and temperature are related via H = const · T 2 .
The SU (3) equation of state (P (T ), s(T ), I(T )) are calculated within the Field Correlator Method both in the confined and the deconfined phases. The basic dynamics in our approach is contained in the vacuum correlators, both of the colorelectric (CE) and colormagnetic (CM) types, which ensure CE and CM confinement below T c and CM confinement and Polyakov loops above T c . The resulting values of T c and P (T ), I(T ), s(T ) are in good agreement with lattice measurements. * agasian@itep.ru † lukashov@phystech.edu ‡ simonov@itep.ru
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