[Paper Review] Theoretical and Experimental Constraints for the Equation of State of Dense and Hot Matter

Rajesh Kumar, Verônica Dexheimer+58 more|arXiv (Cornell University)|Mar 29, 2023

High-Energy Particle Collisions ResearchPhysics and Astronomy687 references10 citations

TL;DR

A comprehensive review compiling lattice QCD, perturbative QCD, chiral EFT, heavy-ion, low-energy nuclear physics, and astrophysical constraints to map the QCD equation of state across dense and hot regimes.

ABSTRACT

This review aims at providing an extensive discussion of modern constraints relevant for dense and hot strongly interacting matter. It includes theoretical first-principle results from lattice and perturbative QCD, as well as chiral effective field theory results. From the experimental side, it includes heavy-ion collision and low-energy nuclear physics results, as well as observations from neutron stars and their mergers. The validity of different constraints, concerning specific conditions and ranges of applicability, is also provided.

Motivation & Objective

• Summarize first-principles theoretical constraints on the EoS from lattice QCD, perturbative QCD, and chiral EFT.
• Synthesize experimental constraints from heavy-ion collisions, low-energy nuclear physics, and neutron-star observations.
• Clarify the valid regimes and applicability ranges of different constraints for dense and hot matter.
• Discuss how these constraints connect to the QCD phase diagram and to astrophysical observables.

Proposed method

• Present and compare theoretical constraints derived from lattice QCD at finite temperature and small chemical potential.
• Describe resummed perturbative QCD approaches applicable at high temperature and/or density.
• Explain chiral effective field theory as a low-energy framework with quantified uncertainties.
• Outline how experimental observations constrain the EoS across heavy-ion, low-energy nuclear physics, and astrophysical domains.
• Summarize how these constraints map onto the QCD phase diagram and guide model construction.

Experimental results

Research questions

• RQ1 What are the reliable theoretical constraints on the EoS of dense and hot matter from lattice QCD, pQCD, and χEFT, and in which regimes do they apply?
• RQ2 How do experimental data from heavy-ion collisions, low-energy nuclear physics, and neutron-star observations constrain the EoS, and what are the caveats in interpreting these constraints?
• RQ3 How do these theoretical and experimental constraints combine to constrain the QCD phase diagram?
• RQ4 What mechanisms address the hyperon puzzle and other high-density degrees of freedom in neutron-star matter?

Key findings

• Lattice QCD provides EoS information at zero or small baryon density and high temperature, indicating a crossover between hadronic and quark-gluon plasma phases.
• Perturbative QCD becomes reliable at high temperature or density after resummation, with specific applicability ranges in T and μB.
• Chiral EFT offers systematic, uncertainty-quantified guidance for low-density nuclear matter, with Bayesian methods improving uncertainty estimates.
• Experimental data from heavy-ion collisions probe finite T and μB and can inform the EoS via model-to-data comparisons, though dynamical model dependencies exist.
• Low-energy nuclear physics constrains symmetry energy and saturation properties, informing neutron-star matter at intermediate densities, while astrophysical observations constrain high-density EoS through masses, radii, and tidal deformabilities.
• Hyperon presence in neutron stars introduces the hyperon puzzle, requiring additional repulsion or phase transitions to maintain consistency with massive neutron stars.