**Feynman diagrams and gravity join forces to crack the QGP**

Abstract:

In many systems such as the quark-gluon plasma (QGP), it is necessary to combine perturbative and non-perturbative degrees of freedom to describe collective behavior. Multiple energy scales are typically involved in processes such as thermalization. Semi-holography is a proposal to build effective
theories of these systems in which it is postulated that non-perturbative strongly coupled physics is described via holographic duality by an appropriate classical gravity theory that should be constructed in order to cure absence of Borel resummability of perturbative dynamics. After briefly discussing the
general formulation, we will describe the phenomenological construction of the semi-holographic model for QGP where we have recently succeeded in combining the kinetic theory of hard gluons with the strongly coupled fluid description of the soft sector. Our latest results demonstrate novel aspects of collective
excitations. Finally, we will present a conjecture about how equi-partitioning of energy which is necessary for thermalization happens in the semi-holographic picture.