Strong interaction at finite temperature

We review two methods discussed in the literature to determine the effective parameters of strongly interacting particles as they move through a heat bath. The first one is the general method of chiral perturbation theory, which may be readily applied to this problem. The other is the method of thermal QCD sum rules. We show that, when the spectral sides of the sum rules are calculated correctly, they do not lead to any new results, but reproduce those of the vacuum sum rules.     

Baryon terms in lattice gauge theories at finite temperature

We consider Susskind fermions on ad-dimensional lattice interacting withSU(n) gauge fields at finite temperature in the strong coupling limit. We demonstrate that the baryon terms can be treated perturbatively. Their effect on the Wilson loop parameter is calculated.     

Induced Chern-Simons term in lattice QCD at finite temperature

The general conditions for the Chem-Simons action to be induced as a non-universal contribution of fermionic determinant are formulated in finite-temperature lattice QCD. The dependence of the corresponding coefficient in the action on non-universal parameters (chemical potentials, vacuum features, etc.) is explored. Special attention is paid to the role of A₀-condensate if it is available in this theory.     

Complex heavy-quark potential at finite temperature from lattice QCD

We calculate for the first time the complex potential between a heavy quark and antiquark at finite temperature across the deconfinement transition in lattice QCD. The real and imaginary part of the potential at each separation distance r is obtained from the spectral function of the thermal Wilson loop. We confirm the existence of an imaginary part above the critical temperature T(C), which grows as a function of r and underscores the importance of collisions with the gluonic environment for the melting of heavy quarkonia in the quark-gluon plasma.     

On planar fermions with quartic interaction at finite temperature and density

We study the breaking of parity symmetry in the 2+1 Gross-Neveu model at finite temperature with chemical potential μ, in the presence of an external magnetic field. We find that the requirement of gauge invariance, which is considered mandatory in the presence of gauge fields, breaks parity at any finite temperature and provides for dynamical mass generation, preventing symmetry restoration for any non-vanishing μ. The dynamical mass becomes negligibly small as temperature is raised. Received 4 April 2002 / Received in final form 12 July 2002 Published online 15 October 2002 RID="a" ID="a"e-mail: cabra@venus.fisica.unlp.edu.ar     

A quantum field theory of lattice dynamics at finite temperature

A quantum field theoretical treatment of three-dimensional cubic crystals at finite temperature is presented from the view-point of the spontaneous breakdown of the spatial translational invariance using thermo field theory. The effective interaction Hamiltonian is constructed by taking into account the dynamical map of the molecular density operator which is obtained from the Ward-Takahashi relations. The acoustic phonons are expected to be the excitation of particle-hole pairs. The conventional secular equation for the lattice vibrations is obtained by neglecting some quantum effects in the Bethe-Salpeter equation for the molecular density fluctuations. The phonon spectra, the phonon propagators and the dynamical map of the molecular density operator are calculated at finite temperature.     

Incorporating dynamical light quarks in lattice QCD at finite temperature

Using the pseudo-fermion Monte Carlo method we investigate the chiral and the deconfinement phase transitions in the SU(3) gauge theory with dynamical staggered fermions on a 6³ × 2 lattice. The energy density of the gluonic sector ε_G, the average thermal Wilson loop |L| and the order parameter are found to have a rapid variation in the same range of β (=6/g²). The variation is similar to that observed in the quenched theory but is at a smaller value of β.     

Zero and finite temperature phase diagram of the spinless fermion model in infinite dimensions

The phase diagram of the model of spinless fermions with repulsive nearest neighbour interaction is calculated analytically on a hypercubic lattice in infinite dimensions (d → ∞). In spite of its simplicity the model displays a rich phase diagram depending on the doping δ, the interaction U and the temperature T. The system can be in the homogeneous phase (HOM), the nonsegregated AB charge density wave (AB-CDW), the AB phase separation region (PS-AB/HOM; coexistence of AB-CDW and HOM), the incommensurate phase (IP) or the IP phase separation region (PS-AB/IP; coexistence of AB-CDW and IP). We identify three important values of the interaction U_IPL = 0.572 < U_IPH = 1.914 < U_IP/PS = 4.212 which distinguish four intervals of U. These imply four different types of phase diagrams. In all the three phase diagrams with U below U_IP/PS the IP appears. We propose a new general ansatz for the order parameter of this phase. A competition between the IP, the PS-AB/IP and the PS-AB/HOM is found. The relevance of our findings for the phase scenario of the Hubbard model is shown.     

带有2+1味道Wilson费米子的格点量子色动力学在有限温度、有限密度下的相变

利用格点规范理论研究了带有2＋1味道费米子的量子色动力学在有限密度及温度下的相变问题,研究了去禁闭相变与化学势和裸质量参数之间的依赖关系,并利用有限体积效应分析以及Monte Carlo模拟的演化序列所反映出的特点对相变的类型做了确认,给出了相结构图. 关键词： 格点量子色动力学 相变     

Piezoelectric lattice vibrations at optical frequencies

A relationship is proposed between the piezoelectric coefficient and the dielectric constant (or refractive index) based on classical dispersion theory. Piezoelectric lattice vibrations are associated with ionic polarizations at optical frequencies. This relation is applied to study the piezoelectric lattice vibrations in α-quartz, and agreement is found between the calculated and the measured value of the piezoelectric coefficient. No direct experimental method for measurement of piezoelectric coefficients at optical frequencies exists; however, in terms of the proposed relation, piezoelectric coefficients at optical frequencies can be evaluated from infrared reflection measurements.     

The non-linear interaction of a powerful light beam with crystal lattice vibrations

The interaction of a powerful light beam with a one dimensional crystal lattice consisting of anisotropic and axially symmetric molecules is discussed. Translational and rotational vibrations are taken into account.     

Theory of damping and fluctuations of the polariton due to its interaction with lattice vibrations

We present a model which describes the influence of lattice vibrations on the excitonpolariton. We solve the density matrix equation for the coupled photon-exciton-phonon system where the model of Haken and Strobl is used to describe the exciton phonon coupling which is responsible for the incoherent part of the motion. Our model allows us to calculate the dispersion relation of the damped polariton. Furthermore we may understand the optical absorption of crystals in the polariton picture. Our solution also exhibits the phenomenon of nonclassical light absorption.     

Universality in finite temperature lattice QCD

In the lattice regularization of QCD, physical results must be independent of the choice of lattice action. Finite temperature thermodynamics provides a very sensitive test of this universality, providing a functional comparison between the predictions of different actions. We study thermodynamics using Wilson's, Manton's and Villain's actions as well as the mixed fundamental-adjoint form of Bhanot and Creutz. Our results support universality in all cases, but indicate that in general the region of couplings in present lattice calculations requires the inclusion of higher order effects in the perturbative solution of the renormalization group equation.     

Semiclassical treatment of induced schwinger processes at a finite temperature

The induced pair production in an external field at a finite temperature is considered. An one-loop correction to the Green’s function of a meson is calculated semiclassically within the framework of a saddle-point analysis of the Schwinger proper time integrals. This correction appears to be exponentially small in terms of an inverse temperature dependence. The low-temperature limit is shown to be in full agreement with previously obtained zero-temperature results. The corrections in the low-temperature limits are estimated up to the leading exponential and preexponential terms. A comparison is made to earlier calculations of the vacuum decay. The text was submitted by the authors in English.