Seminar

Non-renormalizability of the classical-statistical approximation

By
Thomas Epelbaum (IPhT, Saclay)
Date
Place
Aula 507 (Facultat de Física, UB)
seminar ICCUB
In recent years, the classical-statistical approximation (CSA), that aims at (among other) describing out of equilibrium systems, has experienced great successes. In particular, in the framework of heavy-ion-collisions, its use gave [1307.1765,1307.2214] the first hints of a possible fast “hydrodynamization” (isotropization of the pressure tensor, very low viscosity over entropy ratio) of the quark gluon plasma, in agreement with the early hydrodynamical description of the experimental outcomes.

But a recent study [1312.5216]] has triggered new interrogations on the range of validity of the CSA, showing a strong cutoff dependence in the numerical simulations of a scalar toy model. The question therefore lies down to the following one: is the CSA renormalizable? If the answer to this question was positive, then it would simply meant that the renormalization work was not done properly in previous studies (including [1312.5216]). But as we will argue in this talk, the CSA is indeed non-renormalizable [1402:0115]. The key reason behind this fact is that a vertex is missing in the CSA when compared to the full fledge quantum theory. This missing vertex forbids some non-trivial cancellations in one loop four point functions that do happen in the full theory.

In the present talk, after having briefly recalled the recent uses and successes of the CSA, we will elaborate on its non-renormalizability. We will conclude by presenting a possible modification of the CSA in order to extend its range of validity, as well as advocating what should be from now on the interpretation of the CSA results.
NOTES

Notice unusual day