An ongoing program of evaluating transverse momentum-dependent (TMD)
observables in hadrons within Lattice QCD is reviewed, summarizing
recent progress with respect to several challenges faced by such
calculations. These lattice calculations are based on a definition of
TMDs through hadronic matrix elements of quark bilocal operators,
including an appropriate gauge connection between the quarks.
Results presented include data on the Sivers and Boer-Mulders effects,
exhibiting the decisive role of the gauge connection in encoding
information about the struck quark in a deep inelastic scattering
process. Generalizing these TMD calculations by connecting them with
information about quark transverse position in the hadron allows one
to access quark orbital angular momentum and provide a new perspective
on the proton spin puzzle - the question of how the proton's spin
arises from the spins and orbital angular momenta of its constituents.
Session: Low-x, PDFs and hadronic final states, high pT