Thermal Conductivity and Chiral Critical Point in Heavy Ion Collisions

TL;DR

This paper develops a model of thermal conductivity near the QCD critical point and studies how hydrodynamic fluctuations influence observables in heavy ion collisions, potentially allowing detection of the critical point.

Contribution

It introduces a mode coupling theory-based model of thermal conductivity that diverges at the critical point and analyzes its impact on collision observables.

Findings

Fluctuations increase near the critical point

Correlation functions show enhanced signals close to the critical point

Method can help identify the critical point in experiments

Abstract

Background: Quantum Chromodynamics is expected to have a phase transition in the same static universality class as the 3D Ising model and the liquid-gas phase transition. The properties of the equation of state, the transport coefficients, and especially the location of the critical point are under intense theoretical investigation. Some experiments are underway, and many more are planned, at high energy heavy ion accelerators. Purpose: Develop a model of the thermal conductivity, which diverges at the critical point, and use it to study the impact of hydrodynamic fluctuations on observables in high energy heavy ion collisions. Methods: We apply mode coupling theory, together with a previously developed model of the free energy that incorporates the critical exponents and amplitudes, to construct a model of the thermal conductivity in the vicinity of the critical point. The effect of the thermal conductivity on correlation functions in heavy ion collisions is studied in a boost invariant hydrodynamic model via fluctuations, or noise. Results: We find that the closer a thermodynamic trajectory comes to the critical point the greater is the magnitude of the fluctuations in thermodynamic variables and in the 2-particle correlation functions in momentum space. Conclusions: It may be possible to discern the existence of a critical point, its location, and thermodynamic and transport properties near to it in heavy ion collisions using the methods developed here.