The paper introduces nuclear double-parton distributions (DPDs) as convolutions of nucleon DPDs with nuclear light-cone momentum distributions. It focuses on the DPS1 mechanism, in which both active partons originate from the same nucleon inside the nucleus, and defines a double-EMC ratio from double-parton-scattering cross sections. This observable is proposed as a potentially more sensitive probe of bound-nucleon structure than the conventional EMC ratio obtained from single-parton distributions or deep-inelastic-scattering structure functions.
The authors compare factorized and fully correlated nucleon-DPD models that produce similar conventional EMC ratios but substantially different double-EMC ratios. However, the paper presents this proposed connection between nuclear DPS and the origin of the EMC effect only as a conjecture; establishing whether measurements or calculations of nuclear DPS can genuinely reveal the underlying mechanism remains unresolved. The DPS2 contribution, involving partons from different nucleons, is also left for future analyses, although the stated conjecture specifically concerns the broader ability of nuclear DPS to provide new insight into the EMC effect.