Sökning: "Many-body perturbation theory"

Hittade 5 uppsatser innehållade orden Many-body perturbation theory.

1. 1. Atomic Structure Calculations Using Configuration-Interaction And Many-Body Perturbation Theory For Spectral Modelling Of Neutron Star Mergers : Example Of Ce I - Iv

   L3-uppsats, Uppsala universitet/Teoretisk fysik

   Författare :Fredrik Plane; [2023]
   Nyckelord :Computational atomic physics; Atomic physics; Physics; Astronomy; Astrophysics; Neutron stars; Stars; Relativisitc atomic physics; Configuration-interaction; Perturbation theory; Many-body perturbation theory;

   Sammanfattning : The binary neutron star merger of 2017 and its corresponding electromagnetic signature resembling that of a kilonova has been one of the most groundbreaking astrophysical occurrences in the last decade. Indications of r-process nucleosynthesis in this event presents new opportunities for learning about the astrophysical origin of heavy elements. LÄS MER

3. 2. Beyond the Gross-Pitaevskii Equation: A Perturbative Approach

   Master-uppsats, Lunds universitet/Fysiska institutionen; Lunds universitet/Teknisk fysik (CI)

   Författare :Anton Johansson; [2023]
   Nyckelord :Gross-Pitaevskii; Beyond mean-field; Many-body Perturbation Theory; Bose-Einstein Condensate; BEC; Physics and Astronomy;

   Sammanfattning : We propose and implement a beyond Gross-Pitaevskii approach based on Many-Body Perturbation theory (MBPT) for the study of Bose-Einstein Condensate (BECs) ground states. Two partitions of the system Hamiltonian are considered. LÄS MER

4. 3. Time-resolved x-ray diffraction study of longitudinal optical phonons in zincblende semiconductors

   Master-uppsats, Lunds universitet/Atomfysik; Lunds universitet/Fysiska institutionen

   Författare :Lassi Linnala; [2022]
   Nyckelord :femtosecond THz radiation; ultrafast x-ray diffraction; pump-probe; longitudinal optical phonons; zincblende semiconductors; anharmonic decay; density functional perturbation theory; Physics and Astronomy;

   Sammanfattning : Anharmonic decay of longitudinal optical (LO) phonons in zincblende semiconductors is not at present well characterized due to the polar and many-body nature of the problem. Femtosecond THz radiation offers a novel route to this study, as the interaction of this radiation is directly with the phonon lattice and these THz excited phonons do not have enough energy to excite electrons over the band gap. LÄS MER

5. 4. Beyond Mean-Field Description of Bose-Einstein Condensate

   Kandidat-uppsats, Lunds universitet/Matematisk fysik; Lunds universitet/Fysiska institutionen

   Författare :Daniel Larsson Persson; [2021]
   Nyckelord :Bose-Einstein condensate; BEC; dilute; non-uniform; quantum depletion; second quantisation; mean field; mean-field approximation; the Gross-Pitaevskii equation; Gross-Pitaevskii; perturbation theory; many-body perturbation theory; Rayleigh-Schrödinger perturbation theory; Rayleigh-Schrödinger; Epstein-Nesbet perturbation theory; Epstein-Nesbet; quantum ring; Physics and Astronomy;

   Sammanfattning : This thesis work is on the theoretical description of dilute Bose-Einstein condensates (BEC) that are non-uniform, meaning that more than one single-particle state is occupied. This phenomenon is usually called quantum depletion. LÄS MER

7. 5. Machine-Learning for Lattice Models in and out of Equilibrium

   Master-uppsats, Lunds universitet/Matematisk fysik; Lunds universitet/Fysiska institutionen

   Författare :Johannes Sandberg; [2021]
   Nyckelord :Physics and Astronomy;

   Sammanfattning : Machine-learning methods have in recent years seen a great deal of use in condensed matter physics. In this thesis we apply such methods, specifically machine-learning with artificial neural networks, to the equilibrium and non-equilibrium description of the Hubbard and Hubbard-Holstein models. LÄS MER