  In a previous work hep-ph/0203165 we have studied propagation of relativistic
particles in the bulk for some of most popular brane models. Constraints have
been put on the parameter space of these models by calculating the time delay
due to propagation in the bulk of particles created during the interaction of
Ultra High Energy Cosmic Rays with protons in the terrestrial atmosphere. The
question was however raised that probability of hard processes in which bulk
modes can be produced is small and consequently, the tiny flux of UHECRs can
not constrain brane models. Here we use Color Glass Condensate (CGC) model to
show that effects of extra dimensions are visible not only in hard processes
when the incoming particle hits a massive Kaluza-Klein mode but also through
the modification of soft/semi-hard parton distribution. At classical level, for
an observer in the CM frame of UHECR and atmospheric hadrons, color charge
sources are contracted to a thin sheet with a width inversely proportional to
the energy of the ultra energetic cosmic ray hadron and consequently they can
see an extra dimension with comparable size. Due to QCD interaction a short
life swarm of partons is produced in front of the sheet and its partons can
penetrate to the extra-dimension bulk. This reduces the effective density of
partons on the brane or in a classical view creates a delay in the arrival of
the most energetic particles if they are reflected back due to the warping of
the bulk. In CGC approximation the density of swarm at different distance from
the classical sheet can be related and therefore it is possible (at least
formally) to determine the relative fraction of partons in the bulk and on the
brane at different scales. Results of this work are also relevant to the test
of brane models in hadron colliders like LHC.
