Black Holes and Revelations: Investigating Black Holes using String Theory, SYK-Models and Quark-Gluon Plasmas

In this research work, we investigate black hole physics from several points of view, separated into three parts. In the first part, we investigate black holes using explicit string theory and M-theory techniques. Firstly, we consider black holes in string theory with duality twists. Such twists allow us to break supersymmetry, which is naturally present in superstring theory but not in our universe. We investigate several brane configurations and the possibilities of preserving them with different duality twists. Secondly, we embed certain classes of rotating black holes into M-theory. This embedding lays the groundwork for extending the geometric dual of I-extremization and c-extremization to theories arising from the near-horizon of rotating black holes and black strings respectively. The second part of the thesis consists of an extension to the SYK-model by including also certain auxiliary bosons. On top of the N Majorana fermions, we have thus also added M bosons. We investigate the properties of the model as a function of the ratio M/N, where, for example, at M=N it is similar to supersymmetric SYK. The SYK-model begets its interest due to the expected duality to two-dimensional black holes. The last part investigates heavy-ion collisions and the quark-gluon plasmas that are created in such collisions. The collision beams are very difficult to align perfectly, and in practice, there are always ‘spectating’ particles that don’t participate in the creation of the quark-gluon plasma. We investigate the electromagnetic fields that arise due to such spectating particles (as well as the less-important participators) at heavy-ion collisions, and their effect on the expansion of the quark-gluon plasma.