  A brief introduction of the relationship of string percolation to the Quantum
Chromo Dynamics (QCD) phase diagram is presented. The behavior of the Polyakov
loop close to the critical temperature is studied in terms of the color fields
inside the clusters of overlapping strings, which are produced in high energy
hadronic collisions. The non-Abelian nature of the color fields implies an
enhancement of the transverse momentum and a suppression of the multiplicities
relative to the non overlapping case. The prediction of this framework are
compared with experimental results from the SPS, RHIC and LHC for $pp$ and AA
collisions.
  Rapidity distributions, probability distributions of transverse momentum and
multiplicities, Bose-Einstein correlations, elliptic flow and ridge structures
are used to evaluate these comparison. The thermodynamical quantities, the
temperature, and energy density derived from RHIC and LHC data and Color String
Percolation Model (CSPM) are used to obtain the shear viscosity to entropy
density ratio ($\eta/s$). It was observed that the inverse of ($\eta/s$)
represents the trace anomaly $\Delta =(\varepsilon-3P)/T^{4}$. Thus the
percolation approach within CSPM can be successfully used to describe the
initial stages in high energy heavy ion collisions in the soft region in high
energy heavy ion collisions. The thermodynamical quantities, temperature and
the equation of state are in agreement with the lattice QCD calculations. Thus
the clustering of color sources has a clear physical basis although it cannot
be deduced directly from QCD.

Nuclear Theory;High Energy Physics - Phenomenology;Nuclear Experiment