Abstract: The collision of two gravitationally interacting, ultra-relativistic, extended sources is being examined. This investigation classifies the transverse distributions that are collided according to whether one or two (a small and a large) apparent horizons may or may not be formed in a flat background in 4 dimensions. The study suggests a universal behavior in the produced entropy and, the elimination of the possibility in observing black holes (BHs) at the LHC in the absence of extra dimensions. On the other hand, including extra dimensions, and assuming that the matter is localized (dense) enough in those directions, opens new avenues in creating BHs at TeV scales.
The investigation is carried further to $AdS_5$ backgrounds and makes connections with QGP. In particular, it seems that a BH is formed if and only if the (central collision) energy is sufficiently large compared to the transverse scale of the corresponding gauge theory side stress-tensor. This implies that a result, which is in accordance with the current intuition and data: QGP is formed only at high enough energies compared to $Lambda_{QCD}$, even for central processes. Incorporating weak coupling physics and in particular the Color Glass Condensate (CGC) model, a satisfactory fitting with the RHIC and the LHC data for multiplicities may be established.