Calculation of Power Spectrum in the Little Bangs

TL;DR

This paper estimates the power spectrum of particle momentum fluctuations in relativistic heavy ion collisions using methods analogous to cosmic microwave background analysis, incorporating perturbations evolved via Boltzmann transport in an expanding QGP.

Contribution

It introduces a novel approach to calculate the power spectrum in heavy ion collisions, linking it to flow harmonics and perturbations in phase space.

Findings

Power spectrum is enhanced by non-equilibrium perturbations.

Variation of power spectrum with temperature reveals non-ideal effects.

A relation between power spectrum and flow harmonics is established.

Abstract

The power spectrum of fluctuations in the momentum distributions of particles have been estimated with optical Glauber and Monte-Carlo Glauber initial conditions for relativistic heavy ion collisions. The evaluation procedure adopted in this work is analogous to the one used in the calculation of power spectrum in Cosmic Microwave Background Radiation (CMBR). The power spectrum due to perturbations in the phase space distribution of the particles has also been evaluated. The perturbation in phase space has been evolved through the Boltzmann transport equation in an expanding quark gluon plasma (QGP) background. The expansion of the QGP has been treated within the purview of (3+1) dimensional relativistic hydrodynamics. We observe that the non-equlibrium effects introduced as perturbations in the phase space distributions can be traced from the enhancement of the power spectrum as well as through its variation with temperature which is distinctly different from the case of vanishing perturbation. A relation has been derived between the power spectrum and the flow harmonics.