| Popis: |
Quantum Chromodynamics (QCD) poses a challenge in calculating physical phenomena in low energy scales due to its strongly coupled character. The tools available for understanding this region of QCD are limited. One such tool is gauge/gravity duality which promises to attack strongly coupled related phenomena, at least in a qualitative level, by using the conjectured equivalence between string theory and some classes of quantum field theories (gauge/gravity duality). In this thesis strongly coupled 3+1d and 2+1d field theories are explored by using D3/D7 and D3/D5 brane systems respectively. These theories exhibit some QCD-like characteristics like chiral symmetry breaking and confinement. The main focus of the following chapters is understanding chiral phase transitions in those theories and constructing their phase diagrams in finite temperature and chemical potential. Chiral symmetry breaking is induced in these holographic brane setups by turning on a background magnetic field or by choosing an appropriate running dilaton profile. The phase diagrams for each field theory considered are mapped, giving a rich structure of first, second and BKT holographic transitions. Some successful attempts where made to reproduce the standard QCD phase diagram, in the running dilaton scenario. Also, in the running dilaton case wrapped D5 branes where used to introduce holographic baryons. The baryonic phase, for some range of the parameter space, participates in the phase diagram and it is found in the regime expected from QCD. Finally, chiral phase transitions with energy scale where explored as well as their holographic effective potentials for various D3/D7 and D3/D5 systems. |
