Estakhr variables and Flow- like Observables in Heavy Ion Collision

The Estakhr variables are numerical quantities that encode the density, Current density, and angles of Heavy ion in a scattering process in a Lorentz-invariant fashion. If the Minkowski Metric is chosen to be (+,-,-,-) , the Estakhr variables $c_1, c_2,c_3$ are then defined by: $c_1=(J_1+J_2)^2=(J_3+J_4)^2$, $c_2=(J_1-J_3)^2=(J_2-J_4)^2$, $c_3=(J_1-J_4)^2=(J_2-J_3)^2$, Where J$_1$ and J$_2$ are the four-Current density of the incoming heavy Ions and J$_3$ and J$_4$ are the four-Current density of the outgoing heavy Ions, and we are using Planck units (c=1). and then $\sum_{i=1}^{3}c_i=\sum_ {i=1}^{4}\rho_i^2$