Abstract
The energy-momentum tensor plays an important role in QCD thermodynamics. Its expectation value contains information of the pressure and the energy density as its diagonal part. Further properties like viscosity and specific heat can be extracted from its correlation function. A nonperturbative evaluation of it on the lattice is called. Recently, a new method based on the gradient flow was introduced to calculate the energy-momentum tensor on the lattice and has been successfully applied to quenched QCD. In this paper, we apply the gradient flow method to calculate the energy-momentum tensor in ()-flavor QCD adopting a nonperturbatively -improved Wilson quark action and the renormalization group-improved Iwasaki gauge action. As the first application of the method with dynamical quarks, we study at a single but fine lattice spacing with heavy and quarks () and approximately physical quark (). With the fixed-scale approach, temperature is varied by the temporal lattice size at a fixed lattice spacing. Performing simulations on lattices with to 4, the temperature range of is covered. We find that the results of the pressure and the energy density by the gradient flow method are consistent with the previous results using the -integration method at (), while the results show disagreement at (), presumably due to the small- lattice artifact of . We also apply the gradient flow method to evaluate the chiral condensate taking advantage of the gradient flow method that renormalized quantities can be directly computed avoiding the difficulty of explicit chiral violation with lattice quarks. We compute the renormalized chiral condensate in the scheme at renormalization scale with a high precision to study the temperature dependence of the chiral condensate and its disconnected susceptibility. Even with the Wilson-type quark action which violates the chiral symmetry explicitly, we obtain the chiral condensate and its disconnected susceptibility showing a clear signal of pseudocritical temperature at related to the chiral restoration crossover.
11 More- Received 9 November 2016
DOI:https://doi.org/10.1103/PhysRevD.96.014509
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