The Regge asymptotics of 2 -> N scattering in QCD and gravity: from amplitudes to shockwave collisions

Abstract: We discuss the structure of 2-> N scattering in QCD and gravity in high energy Regge asymptotics and outline remarkable similarities between the two. In the QCD case, the rapid growth of the N-gluon amplitude, described by the BFKL equation, leads to the emergence of nonperturbative classical lumps that unitarize the cross-section at fixed impact parameter. We describe the resulting shockwave picture of gluon radiation in hadron-hadron collisions that leads to the formation of a quark-gluon plasma. The ``gravitational BFKL” 2->N amplitude grows far more rapidly and it has been argued on general grounds that classicalization and unitarization must result similarly to the QCD case. We compute gravitational radiation and shockwave propagators in the collision of gravitational shockwaves and demonstrate their double copy structure to QCD in the Regge regime. Both soft (Weinberg) and semi-hard (Lipatov) radiation can be understood as classical double copies of QCD radiation.

Note: this will be a meeting of the EMPG with a discussion of arXiv papers at 11am and the seminar itself taking place at 11:30.