Simulation of 3+1D glasma in Milne coordinates I: Development of the framework

We propose a new numerical method for $3+1$D glasma simulation using Milne coordinates. We formulate the classical Yang-Mills field and $3$D classical color current on a lattice at the initial proper time, specified as a moment just before the collision of the two nuclei. By solving the evolution equations, we extract observables of the $3$D glasma at later times. We demonstrate the efficiency of our method in terms of numerical cost and apply it to the central collisions of Au-Au. We also discuss possible further improvements of our method.