This manuscript is the outcome of the subgroup ``PDFs, shadowing and pA
collisions'' from the CERN workshop ``Hard Probes in Heavy Ion Collisions at
the LHC''. In addition to the experimental parameters for pA collisions at
the LHC, the issues discussed are factorization in nuclear collisions, nuclear
parton distributions (nPDFs), hard probes as the benchmark tests of
factorization in pA collisions at the LHC, and semi-hard probes as
observables with potentially large nuclear effects. Also, novel QCD phenomena
in pA collisions at the LHC are considered. The importance of the pA
program at the LHC is emphasized.Comment: The writeup of the working group "PDFs, shadowing and pA
collisions" for the CERN Yellow Report on Hard Probes in Heavy Ion Collisions
at the LHC, 121 pages. Subgroup convenors: K.J. Eskola, J.w. Qiu (theory) and
W. Geist (experiment). Editor: K.J. Eskol