  Double parton distribution functions (dPDF), accessible in high energy
proton-proton and proton nucleus collisions, encode information on how partons
inside a proton are correlated among each other and could represent a tool to
explore the 3D proton structure. In recent papers, double parton correlations
have been studied in the valence quark region, by means of constituent quark
models. This framework allows to understand clearly the dynamical origin of the
correlations and to establish which, among the features of the results, are
model independent. Recent relevant results, obtained in a relativistic
light-front scheme, able to overcome some drawbacks of previous calculations,
such as the poor support, will be presented. Peculiar transverse momentum
correlations, generated by the correct treatment of the boosts, are obtained.
The role of spin correlations will be also shown. In this covariant approach,
the symmetries of the dPDFs are unambiguously reproduced. The study of the QCD
evolution of the model results has been performed in the valence sector,
showing that, in some cases, the effect of evolution does not cancel that of
correlations.
