Anisotropic and out-of-equilibrium quark-gluon plasma

In heavy ion collider experiments which are among others carried out at the LHC at CERN it is possible to produce a new state of matter, the quark-gluon plasma, which is thought to have filled the early universe during the first microseconds after the Big Bang and which could also still exist in the interior of extremely dense stars such as neutron stars. Both in neutron stars and in heavy-ion collisions extremely strong magnetic fields occur which introduce an anisotropy which gives rise to new phenomena. Moreover, the quark-gluon plasma produced in heavy-ion collisions is initially strongly out-of-equilibrium. In order to study the resulting effects, new methods need to be developed. On the one hand, extensive numerical simulations are performed to treat quark-gluon plasma instabilities. On the other hand, new analytical tools are provided through holographic descriptions which emerge from superstring theory. The latter has found a useful connection between strongly coupled quantum field theories and 5-dimensional supergravity theory.

In heavy ion collider experiments which are among others carried out at the LHC at CERN it is possible to produce a new state of matter, the quark-gluon plasma, which is thought to have filled the early universe during the first microseconds after the Big Bang and which could also still exist in the interior of extremely dense stars such as neutron stars. Both in neutron stars and in heavy-ion collisions extremely strong magnetic fields occur which introduce an anisotropy, giving rise to new phenomena. Moreover, the quark-gluon plasma produced in heavy-ion collisions is initially strongly out-of-equilibrium. In order to study the resulting effects, new methods have been developed. For high-energetic degrees of freedom, conventional particle theoretical methods can be employed, whereas for the very strongly coupled low-energy sector, new analytical tools are provided through holographic descriptions which emerge from superstring theory. The latter has yielded a useful analytical and numerical connection between strongly coupled quantum field theories and 5- dimensional supergravity theory. Combining both descriptions in a new semi-holographic methodology, it was possible for the first time to simulate the thermalization of hard (high- energetic) gluons, where the produced heat bath of soft gluons was described by a growing black hole in 5-dimensional curved space. Also for applications to dense nuclear matter in neutron stars, holographic methods were employed and developed further in order to study phase transitions with and without strong magnetic fields.