Obtaining a coherent picture of Single Spin Asymmetries (SSAs) in hard processes has been a longstanding question in QCD.
A particularly puzzling phenomenon, which yet needs to be explained and which seems to persist in preliminary LHC measurements, is the inclusive production of polarized Lambda baryons from unpolarized protons. Experiments show large transverse polarizations, contradicting the expectation from Perturbative QCD that polarization should be small as proportional to both strong coupling constant and struck-quark mass.
In this talk we present a possible mechanism to interpret inclusive Lambda production based on the observations that: 1. A large SSA can be generated only by introducing a phase difference at the amplitude level; 2. Generalized Parton Distributions (GPDs) provide the theoretical tool to realize such a condition at leading twist.