  The observations of global stellar oscillations of post main-sequence stars
by space-based photometry missions allowed to directly determine their internal
rotation. These constraints have pointed towards the existence of angular
momentum transport processes unaccounted for in theoretical models.
Constraining the properties of their internal rotation thus appears as the
golden path to determine the physical nature of these missing dynamical
processes. We wish to determine the robustness of a new approach to study the
internal rotation of post main-sequence stars, using parametric rotation
profiles coupled to a global optimization technique. We test our methodology on
Kepler 56, a red giant observed by the Kepler mission. First, we carry out an
extensive modelling of the star using global and local minimizations
techniques, and seismic inversions. Then, using our best model, we study in
details its internal rotation profile, we adopted a Bayesian approach to
constrain stellar parametric predetermined rotation profiles using a Monte
Carlo Markov Chain analysis of the rotational splittings of mixed modes. Our
Monte Carlo Markov Chain analysis of the rotational splittings allows to
determine the core and envelope rotation of Kepler 56 as well as give hints
about the location of the transition between the slowly rotating envelope and
the fast rotating core. We are able to discard a rigid rotation profile in the
radiative regions followed by a power-law in the convective zone and show that
the data favours a transition located in the radiative region, as predicted by
processes originating from a turbulent nature. Our analysis of Kepler 56
indicates that turbulent processes whose transport efficiency is reduced by
chemical gradients are favoured, while large scale fossil magnetic fields are
disfavoured as a solution to the missing angular momentum transport.
