Speaker
Description
The unpolarized twist-2 (leading) and twist-3 (subleading), T-even,
transverse-momentum dependent quark distributions in the pion are
evaluated for the first time by using the actual solution of a
dynamical equation in Minkowski space. The adopted theoretical framework
is based on the homogeneous Bethe-Salpeter integral equation with
an interaction kernel given by a ladder gluon exchange, featuring an
extended quark-gluon vertex. The masses of quark and gluon as well as
the interaction-vertex scale have been chosen in a range suggested by
lattice-QCD calculations, and calibrated to reproduce
both pion mass and decay constant.
The joint use of the Fock expansion of the pion state facilitates a more
in-depth analysis of the content of the pion Bethe-Salpeter amplitude,
allowing for the first time to determine the gluon contribution to the
quark average longitudinal fraction, that results to be $\sim 6\%$.
The current analysis highlights the role of the gluon exchanges through
quantitative analysis of collinear and transverse-momentum
distributions, showing, e.g. for both leading and subleading-twists, an
early departure from the widely adopted exponential fall-off, for $|{\bf
k}_\perp|^2> m^2$, with the quark mass $\sim \Lambda_{QCD}$.
