Lectures on multi-particle production in the Glasma

Abstract

In the Color Glass Condensate (CGC) effective field theory, colliding sheets of Colored Glass form a strongly interacting, non-equilibrium state called the Glasma. How Colored Glass shatters to form the Glasma, the properties of the Glasma, and how the Glasma thermalizes into a Quark Gluon Plasma(QGP) are questions of central interest in understanding the properties of the strongly interacting matter produced in heavy ion collisions. We argue that these questions can be addressed in the framework of field theories with strong time dependent external sources. Albeit such field theories are non-perturbative for arbitrarily weak coupling, moments of the multiplicity distribution can be computed systematically in powers of the coupling constant. We demonstrate that the average multiplicity can be (straightforwardly) computed to leading order in the coupling and (remarkably) to next-to-leading order as well. We relate our formalism to results from previous 2+1 and 3+1 dimensional numerical simulations of the Glasma fields. The expanding Glasma is unstable; small fluctuations in the initial conditions grow exponentially with the square root of the proper time. Whether this explosive growth leads to early thermalization in heavy ion collisions requires at present a better understanding of these fluctuations on the light cone. In the final lecture, motivated by recent work of Bialas and Jezabek, we discuss the widely observed phenomenon of limiting fragmentation in the CGC framework.