Sökning: "Self-energy"
Visar resultat 1 - 5 av 13 avhandlingar innehållade ordet Self-energy.
1. Self-consistency and the GW-approximation
Sammanfattning : The effects of self-consistency in the GW-approximation are studied. The $GWA$ is known to describe the electronic properties of a wide range of materials very well. However, the calculations made so far have not taken into account the issue of self-consistency, which is implied in the original formulation of the $GWA$. LÄS MER
2. Model Vertices Beyond the GW Approximation
Sammanfattning : We study the effects of local vertex corrections to the self energy of the electron gas. We find that a vertex derived from time-dependent density-functional theory can give accurate self energies without including the explicit time dependence of the exchange-correlation potential provided, however, that a proper decay at large momentum transfer (large q) is built into the vertex function. LÄS MER
3. Hot and Dense Gauge Theories with External Fields
Sammanfattning : In the introductory part of this thesis, I briefly review quantum statistichal mechanics; quantum field theory with external fields; the real and imaginary time formalisms in thermal field theory; and the hard thermal loop resummation. In the second part, consisting of here reprinted research articles, we apply this to quantum electrodynamics and quantum chromodynamics with a background (chromo-) magnetic field in the presence of a heat and charge reservoir. LÄS MER
4. Quantitative Modeling of Gain in Quantum Cascade Lasers under Operational Intensities
Sammanfattning : This thesis adresses modeling of quantum cascade lasers using non-equilibrium Green’s functions. Focus lies on the quantitative modeling of the gain when the systems are exposed to strong laser fields, as under realistic opertional conditions. LÄS MER
5. A study of finite-size and non-perturbative effects on the van der Waals and the Casimir-Polder forces
Sammanfattning : This licentiate thesis addresses two important aspects of the van der Waals and the Casimir-Polder ground-state and excited-state (resonance) interactions between two atoms or molecules. The first is the finite-size effect and the second is the non-perturbative effect. LÄS MER
