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Collective interaction of QCD strings and early stages of high multiplicity pA collisions

We study the early stages of "central" pA and peripheral AA collisions. Several observables indicate that at a sufficiently large number of participant nucleons the system undergoes a transition into a new "explosive" regime. By defining a string-string interaction through the sigma meson exchange and performing molecular dynamics simulation, we argue that one should expect a strong collective implosion of the multi-string "spaghetti" state, creating significant compression of the system in the transverse plane. Another consequence is the collectivization of the "sigma clouds" of all strings into a chirally symmetric fireball. We find that these effects happen provided the number of strings $N_s > 30$ or so, as only such a number can compensate a small sigma-string coupling. These findings should help us to understand the subsequent explosive behavior, observed for the particle multiplicities roughly corresponding to this number of strings.