Title: ``Photon interactions: from Pomerons to Gravitons''
I review recent progress concerning high energy scattering, and in
particular photon interactions, in the vicinity of the unitarity limit,
at both weak and strong coupling. Although the two limits refer to different
gauge theories (QCD at weak coupling, and respectively N=4 SYM at strong
coupling), their comparison is still meaningful since at high energy QCD
itself is nearly conformal. In QCD at weak coupling, the approach towards
the unitarity limit proceeds via multiple scattering and gluon saturation,
as encoded in the Balitsky-JIMWLK equations. At large N_c, this can be also
formulated as an effective theory for BFKL Pomerons, including triple
Pomeron vertices and Pomeron loops. At strong coupling, photon
interactions can be formulated, within the AdS/CFT correspondances, as
graviton exchanges in the dual supergravity theory. I argue that this
leads to unitarity and parton saturation, albeit in rather unusual way:
via successive parton branchings, all the partons fall at very small
values of Bjorken x, below the saturation line, so that there are no
partons (no leading-twist tails for the parton distributions) at large x,
or high Q^2. I particularly emphasize photon interactions within a
strongly coupled `quark-gluon' plasma, because of their potential
relevance for heavy ion physics at RHIC and LHC.