The chiral and deconfinement aspects of the QCD transition (1111.1710v2)

Abstract: We present results on the chiral and deconfinement properties of the QCD transition at finite temperature. Calculations are performed with 2+1 flavors of quarks using the p4, asqtad and HISQ/tree actions. Lattices with temporal extent N_tau=6, 8 and 12 are used to understand and control discretization errors and to reliably extrapolate estimates obtained at finite lattice spacings to the continuum limit. The chiral transition temperature is defined in terms of the phase transition in a theory with two massless flavors and analyzed using O(N) scaling fits to the chiral condensate and susceptibility. We find consistent estimates from the HISQ/tree and asqtad actions and our main result is T_c=154 +/- 9 MeV.

• The paper determines the pseudocritical chiral transition temperature near T_c = 154 ± 9 MeV through lattice simulations with various improved fermion actions.
• The paper employs the chiral condensate, susceptibility, and Polyakov loop to mitigate discretization errors and probe both chiral symmetry restoration and deconfinement.
• The paper validates continuum extrapolation using O(N) scaling functions, offering robust cross-comparison of lattice results and setting a benchmark for future QCD research.

Overview of "The chiral and deconfinement aspects of the QCD transition"

This paper investigates the chiral and deconfinement properties of the Quantum Chromodynamics (QCD) transition at finite temperature using lattice simulations. The computations are carried out by the HotQCD Collaboration, employing three different fermion actions—p4, asqtad, and HISQ/tree—in the framework with 2+1 flavors of quarks.

The primary objective of this paper is to determine the pseudocritical temperature for the chiral phase transition, analyze cutoff effects, and ensure consistency across different discretization schemes employed in lattice QCD simulations. The paper provides a comprehensive comparative analysis, focusing on discretization errors and the subtle interplay between chiral and deconfinement aspects of the QCD transition.

Chiral Condensate and Susceptibility

One of the central focuses of this paper is the paper of the chiral condensate and susceptibility, which probe the restoration of chiral symmetry at high temperatures. The distinct advantage of using different improved staggered fermion actions lies in their ability to mitigate taste-breaking effects, a key source of discretization errors in lattice QCD. The results present a marked improvement in controlling these effects, particularly with the HISQ/tree action, which displays far less deviation from the continuum limit in chiral observables. The paper determination of the chiral transition temperature $T_c$ from the scaling behavior of the chiral condensate and susceptibility is a critical advance, providing estimates that are crucial for understanding the nature of QCD at high temperatures.

Deconfinement Aspects

The paper discusses deconfinement aspects using the Polyakov loop and quark number susceptibilities. These observables are sensitive to the transition from hadronic degrees of freedom to a quark-gluon plasma. The Polyakov loop, in particular, demonstrates consistent behavior across lattice spacings and different actions, indicating reliable descriptions of screening effects inherent to deconfinement. This contributes to a more robust understanding of the QCD phase transition, complementing the insights drawn from chiral observables.

Numerical Analysis and Results

Strong numerical results substantiate the analysis. Notably, the authors provide a pseudocritical temperature estimate of $T_c = 154 \pm 9$ MeV for the chiral transition in the continuum limit at physical quark masses. This result is situated well within the expected range based on earlier calculations but presents a nuanced update with reduced systematic uncertainties and a cross-validated understanding with multiple lattice actions. Moreover, the authors emphasize the significance of applying $O(N)$ scaling functions to derive these results, ensuring that the scalings obtained align with theoretical expectations of universality classes pertinent to QCD.

Implications for Future Research

The findings have significant theoretical implications by validating the continuum extrapolation of key observables and providing fundamental insights that move closer to a definitive characterization of the QCD phase diagram. Practically, this paper paves the way for further refined lattice computations and enhances predictive capabilities regarding the behavior of hadronic matter under extreme conditions, as encountered in heavy-ion collision experiments.

Future research could potentially extend these studies by incorporating additional flavors or other discretization schemes, exploring the effects of a nonzero baryon chemical potential, and examining the critical end-point behaviors to build upon the foundational understanding provided in this research. The nuanced interplay between different aspects of the QCD transition represented here sets a benchmark for high-precision lattice studies in the field.