13 research outputs found
Superconducting properties of the attractive Hubbard model
A self-consistent set of equations for the one-electron self-energy in the
ladder approximation is derived for the attractive Hubbard model in the
superconducting state. The equations provide an extension of a T-matrix
formalism recently used to study the effect of electron correlations on
normal-state properties. An approximation to the set of equations is solved
numerically in the intermediate coupling regime, and the one-particle spectral
functions are found to have four peaks. This feature is traced back to a peak
in the self-energy, which is related to the formation of real-space bound
states. For comparison we extend the moment approach to the superconducting
state and discuss the crossover from the weak (BCS) to the intermediate
coupling regime from the perspective of single-particle spectral densities.Comment: RevTeX format, 8 figures. Accepted for publication in Z.Phys.
IR divergences and kinetic equation in de Sitter space. (Poincare patch; Principal series)
We explicitly show that the one loop IR correction to the two--point function
in de Sitter space scalar QFT does not reduce just to the mass renormalization.
The proper interpretation of the loop corrections is via particle creation
revealing itself through the generation of the quantum averages and dominates over
the anomalous expectation values . For
these harmonics the Dyson--Schwinger equation reduces in the IR limit to the
kinetic equation. We solve the latter equation, which allows us to sum up all
loop leading IR contributions to the Whiteman function. We perform the
calculation for the principle series real scalar fields both in expanding and
contracting Poincare patches.Comment: 33 pages, 6 fig; Language was correcte