  The mixing of graviphotons and dark brane photons to the Standard Model
hypercharge is analyzed in full generality, in weakly-coupled string theory.
Both the direct mixing as well as effective terms that provide mixing after
inclusion of SM corrections are estimated to lowest order. The results are
compared with Effective Field Theory (EFT) couplings, originating in a hidden
large-N theory coupled to the SM. The string theory mixing terms are typically
subleading compared with the generic EFT couplings. The case where the hidden
theory is a holographic theory is also analyzed, providing also suppressed
mixing terms to the SM hypercharge.
