QGP physics from attractor perturbations

The strong longitudinal expansion characteristic of heavy-ion collisions leads to universal attractor behavior of the resulting drop of quark-gluon plasma (QGP) already at very early times. Assuming approximate boost invariance and neglecting transverse expansion at the initial time, we incorporate subsequent transverse dynamics of this system by linearizing the Mueller-Israel-Stewart theory around the transversely homogeneous attractor. The result is a system of coupled ordinary differential equations which describes the proper-time evolution of Fourier modes encoding the transverse structure of the initial energy deposition. The late-time asymptotic behavior of these solutions is described by transseries which make manifest the stability of the attractor against transverse perturbations. In this framework, information about the structure of the plasma in the transverse plane resides mostly in exponentially suppressed corrections to evolution along the attractor, which are not yet negligible at freeze-out. These findings also suggest a simple numerical approach to QGP dynamics using a finite number of Fourier modes. Physical observables can be expressed in terms of the asymptotic data evaluated at freeze-out. We demonstrate the efficacy of this approach by calculating the final multiplicity distributions and collective flow coefficients.