The column vector calculus for Thermo Field Dynamics of relativistic quantum fields

A formalism is discussed which simplifies the calculation of Feynman diagrams at finite temperature.Comment: 10 pages, GSI-Preprint 93-32 (1993

Thermo Field Dynamics and Kinetic Coefficients of a Charged Boson Gas

Thermo Field Dynamics for inhomogeneous systems is generalized to quantum fields with a continuous single-particle mass spectrum. The modification of the hamiltonian in states with a local thermal Bogoliubov symmetry is used to calculate thermal conductivity and diffusion coefficient of pions interacting with hot, compressed nuclear matter.Comment: 27 pages in LaTeX GSI-Preprint 93-45 (1993

Diagonalization of full finite temperature Green's function by quasi-particles

For thermal systems, standard perturbation theory breaks down because of the absence of stable, observable asymptotic states. We show, how the introduction of {\it statistical} quasi-particles (stable, but not observable) gives rise to a consistent description. Statistical and spectral information can be cleanly separated also for interacting systems.Comment: 9 pages in standard LaTe

The Delta-Hole model at Finite Temperature

The spectral function of pions interacting with a gas of nucleons and Delta-33-resonances is investigated using the formalism of Thermo Field Dynamics. After a discussion of the zero Delta-width approximation at finite temperature, we take into account a constant width of the resonance. Apart from a full numerical calculation, we give analytical approximations to the pionic spectral function including such a width. They are found to be different from previous approximations, and require an increase of the effective Delta-width in hot compressed nuclear matter. The results are summarized in an effective dispersion relation for interacting pions.Comment: 34 pages in standard LaTeX GSI-preprint No. GSI-93-2

DAMPING RATE OF A MASSIVE FERMION IN A HOT MEDIUM

In a hot system every excitation acquires a finite lifetime, manifesting itself in a non-zero spectral width. Ordinary damping as well as quantum memory effects arise from this nontrivial spectral function. This report presents a new method for the self-consistent calculation of the spectral width of a fermion coupled to massless bosons of scalar, vector and pseudoscalar type. In accordance with the known procedures of Quantum Electrodynamics, the self-consistent summation of the corresponding Fock diagram eliminates all infrared divergences although the bosons are not screened at all. The solutions for the fermion damping rate are analytical in the coupling constant g , but not analytical in the temperature parameter, i.e., γ ∝ g²T + O(g⁴T log(T /M )) .У гарячому середовищі кожне збудження має скінченний час існування і проявляється ненульовою спектральною шириною. Звичайне затухання, так само як і квантові ефекти пам’яті, отримується з цієї нетривіальної спектральної функції. Дана робота представляє новий метод самоузгодженого розрахунку спектральної ширини ферміона, зв’язаного з безмасовим бозоном скалярного, векторного та псевдоскалярного типів. У відповідності до відомих з квантової електродинаміки процедур самоузгоджене сумування відповідних фоківських діаграм вилучає всі інфрачервоні розбіжності незважаючи на те, що бозони зовсім не екрануються. Розв’язок для константи ферміонного затухання є аналітичним за константою зв’язку g , але не є аналітичним за параметром температури, тобто γ ∝ g²T + O(g⁴T log(T /M ))

Damping rate of a massive fermion in a hot medium

In a hot system every excitation acquires a finite lifetime, manifesting itself in a non-zero spectral width. Ordinary damping as well as quantum memory effects arise from this nontrivial spectral function. This report presents a new method for the self-consistent calculation of the spectral width of a fermion coupled to massless bosons of scalar, vector and pseudoscalar type. In accordance with the known procedures of Quantum Electrodynamics, the self-consistent summation of the corresponding Fock diagram eliminates all infrared divergences although the bosons are not screened at all. The solutions for the fermion damping rate are analytical in the coupling constant g , but not analytical in the temperature parameter, i.e., γ ∝ g²T + O(g⁴T log(T /M )) .У гарячому середовищі кожне збудження має скінченний час існування і проявляється ненульовою спектральною шириною. Звичайне затухання, так само як і квантові ефекти пам’яті, отримується з цієї нетривіальної спектральної функції. Дана робота представляє новий метод самоузгодженого розрахунку спектральної ширини ферміона, зв’язаного з безмасовим бозоном скалярного, векторного та псевдоскалярного типів. У відповідності до відомих з квантової електродинаміки процедур самоузгоджене сумування відповідних фоківських діаграм вилучає всі інфрачервоні розбіжності незважаючи на те, що бозони зовсім не екрануються. Розв’язок для константи ферміонного затухання є аналітичним за константою зв’язку g , але не є аналітичним за параметром температури, тобто γ ∝ g²T + O(g⁴T log(T /M ))

Soft Photons from Off-shell Particles in a Hot Plasma

Considering the propagation of off-shell particles in the framework of thermal field theory, we present the general formalism for the calculation of the production rate of soft photons and dileptons from a hot plasma. This approach is illustrated with an electrodynamic plasma. The photon production rate from strongly interacting quarks in the quark-gluon plasma, which might be formed in ultrarelativistic heavy ion collisions, is calculated in the previously unaccessible regime of photon energies of the order of the plasma temperature within an effective field theory incorporating dynamical chiral symmetry breaking.Comment: 8 pages in RevTeX format, 3 figures uuencoded postscript added. Also available by anonymous ftp at ftp://tpri6c.gsi.de/pub/phenning/qh95ga

The Bose-Einstein correlation function C2(Q)C_2(Q) from a Quantum Field Theory point of view

We show that a recently proposed derivation of Bose-Einstein correlations (BEC) by means of a specific version of thermal Quantum Field Theory (QFT), supplemented by operator-field evolution of the Langevin type, allows for a deeper understanding of the possible coherent behaviour of the emitting source and a clear identification of the origin of the observed shape of the BEC function $C_2(Q)$. Previous conjectures in this matter obtained by other approaches are confirmed and have received complementary explanation.Comment: Some misprints corrected. To be publishe in Phys. Rev.

Mixing and oscillations of neutral particles in Quantum Field Theory

We study the mixing of neutral particles in Quantum Field Theory: neutral boson field and Majorana field are treated in the case of mixing among two generations. We derive the orthogonality of flavor and mass representations and show how to consistently calculate oscillation formulas, which agree with previous results for charged fields and exhibit corrections with respect to the usual quantum mechanical expressions.Comment: 8 pages, revised versio

Chiral symmetry breaking, color superconductivity and color neutral quark matter: a variational approach

We investigate the vacuum realignment for chiral symmetry breaking and color superconductivity at finite density in Nambu-Jona-Lasinio model in a variational method. The treatment allows us to investigate simultaneous formation of condensates in quark antiquark as well as in diquark channels. The methodology involves an explicit construction of a variational ground state and minimisation of the thermodynamic potential. Color and electric charge neutrality conditions are imposed through introduction of appropriate chemical potentials. Color and flavor dependent condensate functions are determined through minimisation of the thermodynamic potential. The equation of state is calculated. Simultaneous existence of a mass gap and superconducting gap is seen in a small window of quark chemical potential within the model when charge neutrality conditions are not imposed. Enforcing color and electric charge neutrality conditions gives rise to existence of gapless superconducting modes depending upon the magnitude of the gap and the difference of the chemical potentials of the condensing quarks.Comment: 13 pages, 6 figures,to appear in Phys. Rev.