The second act of hydro: small perturbations

Understand

Hydrodynamical description of the "Little Bang" in heavy ion collisions is surprisingly successful: here we systematically study propagation of small perturbations %, also treated hydrodynamically.

• Using analytic description of the expanding fireball known as the "Gubser flow", we proceed to linearized equations for perturbations.
• As all variables are separated and all equations solved (semi)analytically, we can collect all the harmonics and reconstruct the complete Green function of the problem, even in the viscous case.
• Applying it to the power spectrum we found acoustic minimum at the $m=7$ and maximum at $m=9$, which remarkably have some evidence for both in the data.