LQCD Data Research Articles

Analysis of static Wilson line correlators from lattice QCD at finite temperature with T-matrix approach

The thermodynamic T-matrix approach is used to study Wilson line correlators (WLCs) for a static quark-antiquark pair in the quark-gluon plasma (QGP). Selfconsistent results that incorporate constraints from the QGP equation of state can approximately reproduce WLCs computed in 2+1-flavor lattice-QCD (lQCD), provided the input potential exhibits less screening than in previous studies. Utilizing the updated potential to calculate pertinent heavylight T-matrices we evaluate thermal relaxation rates of heavy quarks in the QGP. We find a more pronounced temperature dependence for low-momentum quarks than in our previous results (with larger screening), which turns into a weaker temperature dependence of the (temperature-scaled) spatial diffusion coefficient, in fair agreement with the most recent lQCD data.

Heavy-light susceptibilities in a strongly coupled quark-gluon plasma

Quark number susceptibilities as computed in lattice QCD are commonly believed to provide insights into the microscopic structure of QCD matter, in particular its degrees of freedom. We generalize a previously constructed partonic $T$-matrix approach to finite chemical potential to calculate various susceptibilities, in particular for configurations containing a heavy charm quark. At vanishing chemical potential and moderate temperatures, this approach predicts large collisional widths of partons generated by dynamically formed hadronic resonance states which lead to transport parameters characteristic for a strongly coupled system. The quark chemical potential dependence is implemented into the propagators and the in-medium color potential, where two newly introduced parameters for the thermal and screening masses are fixed through a fit to the baryon number susceptibility, $\chi^B_2$. With this setup, we calculate heavy-light susceptibilities without further tuning; the results qualitatively agree with the lattice-QCD (lQCD) data for both $\chi^{uc}_{11}$ and $\chi^{uc}_{22}$. This implies that the lQCD results are compatible with a significant content of broad $D$-meson and charm-light diquark bound states in a moderately hot QGP.

Thermodynamical properties of hot and magnetized quark matter within the SU(2) Polyakov-Nambu-Jona-Lasinio model: vacuum magnetic regularization scheme

In this work we implement the recent proposed vacuum magnetic regularization (VMR) scheme to the two flavor Polyakov–Nambu–Jona-Lasinio model in order to describe some basic thermodynamic properties such as the pressure, entropy and energy density. We show that this procedure allows the evaluation of the renormalized magnetization, which agrees with LQCD data. Potential physical differences are also explored when other three possible regularization schemes are adopted to describe the chiral condensate.

The light-quark mass dependence of the nucleon axial charge

The light-quark mass dependence of the nucleon axial isovector charge (gA) has been analysed up to NNLO, O(p4), in relativistic chiral perturbation theory using extended-on-mass-shell renormalization, without and with explicit Delta(1232) degrees of freedom. In the Delta-less case at this order, the gA(Mpi) dependence of lattice QCD simulations cannot be reproduced using low energy constants extracted from pion-nucleon phenomenology. A good description of these LQCD data is only accomplished in the theory with Delta. From this fit we obtain gA(Mpiphys)=1.260(12) close to the experimental results and d16= -0.88(88) GeV-2 in agreement with pi N-> pi pi N. The sizeable errors are of theoretical origin, reflecting the difference between O(p3) and O(p4) at large Mpi.

Magnetized pole-mass of neutral ρ meson within full RPA evaluation

In this work we calculate the pole-mass of the ρ0 meson with different spin projections sz=0,±1 in the context of the magnetized two-flavor Nambu–Jona–Lasinio model. Making use of the mean field approximation to obtain the effective quark mass as a function of the magnetic field, we apply the random phase approximation (RPA) to the vector channel in order to calculate the polarization function for each spin component. We adopt the magnetic field independent regularization (MFIR) in our evaluations as a method of separating divergences and the Pauli-Villars regularization for the vacuum contributions. The ρ0 meson mass with spin projection sz=±1 is always catalyzed with the magnitude of the magnetic field, showing good agreement with Lattice QCD results. The mass projection sz=0 has a non-monotonic behavior, decreasing until the minimum at eB≲0.15 GeV2, which is in contrast with available LQCD data.

T -matrix approach to quark-gluon plasma

A selfconsistent thermodynamic $T$-matrix approach is deployed to study the microscopic properties of the quark-gluon plasma (QGP), encompassing both light- and heavy-parton degrees of freedom in a unified framework. The starting point is a relativistic effective Hamiltonian with a universal color force. The input in-medium potential is quantitatively constrained by computing the heavy-quark (HQ) free energy from the static $T$-matrix and fitting it to pertinent lattice-QCD (lQCD) data. The corresponding $T$-matrix is then applied to compute the equation of state (EoS) of the QGP in a two-particle irreducible formalism including the full off-shell properties of the selfconsistent single-parton spectral functions and their two-body interaction. In particular, the skeleton diagram functional is fully resummed to account for emerging bound and scattering states as the critical temperature is approached from above. We find that the solution satisfying three sets of lQCD data (EoS, HQ free energy and quarkonium correlator ratios) is not unique. As limiting cases we discuss a weakly-coupled solution (WCS) which features color-potentials close to the free energy, relatively sharp quasiparticle spectral functions and weak hadronic resonances near $T_{\rm c}$, and a strongly-coupled solution (SCS) with a strong color potential (much larger than the free energy) resulting in broad non-quasiparticle parton spectral functions and strong hadronic resonance states which dominate the EoS when approaching $T_{\rm c}$.

Model prediction for temperature dependence of meson pole masses from lattice QCD results on meson screening masses

We propose a practical effective model by introducing temperature ($T$) dependence to the coupling strengths of four-quark and six-quark Kobayashi-Maskawa-'t Hooft interactions in the 2+1 flavor Polyakov-loop extended Nambu-Jona-Lasinio model. The $T$ dependence is determined from LQCD data on the renormalized chiral condensate around the pseudocritical temperature $T_c^{\chi}$ of chiral crossover and the screening-mass difference between $\pi$ and $a_0$ mesons in $T > 1.1T_c^\chi$ where only the $U(1)_{\rm A}$-symmetry breaking survives. The model well reproduces LQCD data on screening masses $M_{\xi}^{\rm scr}(T)$ for both scalar and pseudoscalar mesons, particularly in $T \ge T_c^{\chi}$. Using this effective model, we predict meson pole masses $M_{\xi}^{\rm pole}(T)$ for scalar and pseudoscalar mesons. For $\eta'$ meson, the prediction is consistent with the experimental value at finite $T$ measured in heavy-ion collisions. We point out that the relation $M_{\xi}^{\rm scr}(T)-M_{\xi}^{\rm pole}(T) \approx M_{\xi'}^{\rm scr}(T)-M_{\xi'}^{\rm pole}(T)$ is pretty good when $\xi$ and $\xi'$ are scalar mesons, and show that the relation $M_{\xi}^{\rm scr}(T)/M_{\xi'}^{\rm scr}(T) \approx M_{\xi}^{\rm pole}(T)/M_{\xi'}^{\rm pole}(T)$ is well satisfied within 20% error when $\xi$ and $\xi'$ are pseudoscalar mesons and also when $\xi$ and $\xi'$ are scalar mesons.

Equation of state and transition temperatures in the quark-hadron hybrid model

We analyze the equation of state of 2+1 flavor lattice QCD at zero baryon density by constructing the simple quark-hadron hybrid model that has both quark and hadron components simultaneously. We calculate hadron and quark contribution separately and parameterizing those to match with LQCD data. Lattice data on the equation of state are decomposed into hadron and quark components by using the model. The transition temperature is defined by the temperature at which the hadron component is equal to the quark one in the equation of state. The transition temperature thus obtained is about 215 MeV and somewhat higher than the chiral and the deconfinement pseudocritical temperatures defined by the temperature at which the susceptibility or the absolute value of the derivative of the order parameter with respect to temperature becomes maximum.

Shear viscosity η to electric conductivity σel ratio for the quark–gluon plasma

The transport coefficients of strongly interacting matter are currently subject of intense theoretical and phenomenological studies due to their relevance for the characterization of the quark–gluon plasma produced in ultra-relativistic heavy-ion collisions (uRHIC). We discuss the connection between the shear viscosity to entropy density ratio, η/s, and the electric conductivity, σel. Once the relaxation time is tuned to have a minimum value of η/s=1/4π near the critical temperature Tc, one simultaneously predicts σel/T very close to recent lQCD data. More generally, we discuss why the ratio of (η/s)/(σel/T) supplies a measure of the quark to gluon scattering rates whose knowledge would allow to significantly advance in the understanding of the QGP phase. We also predict that (η/s)/(σel/T), independently on the running coupling αs(T), should increase up to about ∼20 for T→Tc, while it goes down to a nearly flat behavior around ≃4 for T≥4Tc. Therefore we in general predict a stronger T dependence of σel/T with respect to η/s that in a quasi-particle approach is constrained by lQCD thermodynamics. A conformal theory, instead, predicts a similar T dependence of η/s and σel/T.

Quark number densities at imaginary chemical potential inNf=2lattice QCD with Wilson fermions and its model analyses

We investigate temperature ($T$) dependence of quark number densities ($n_q$) at imaginary and real chemical potential ($\mu$) by using $N_f = 2$ lattice QCD and the hadron resonance gas (HRG) model. Quark number densities are calculated at imaginary $\mu$ with lattice QCD on an $8^2 \times 16 \times 4$ lattice with the clover-improved $N_f =2$ Wilson fermion action and the renormalization-group-improved Iwasaki gauge action. The results are consistent with the previous results of the staggered-type quark action. The $n_q$ obtained are extrapolated to real $\mu$ by assuming the Fourier series for the confinement region and the polynomial series for the deconfinement region. The extrapolated results are consistent with the previous results of the Taylor expansion method for the reweighting factor. The upper bound $(\mu/T)_{\mathrm{max}}$ of the region where the extrapolation is considered to be reliable is estimated for each temperature $T$ . We test whether $T$ dependence of nucleon and $\Delta$-resonance masses can be determined from LQCD data on $n_q$ at imaginary $\mu$ by using the HRG model. In the test calculation, nucleon and $\Delta$-resonance masses reduce by about 10% in the vicinity of the pseudocritical temperature.

Baryon chiral perturbation theory with Wilson fermions up to $${\mathcal {O}}(a^2)$$ O ( a 2 ) and discretization effects of latest $$n_f=2+1$$ n f = 2 + 1 LQCD octet baryon masses

We construct the chiral Lagrangians relevant in studies of the ground-state octet baryon masses up to $\mathcal{O}(a^2)$ by taking into account discretization effects and calculate the masses up to $\mathcal{O}(p^4)$ in the extended-on-mass-shell scheme. As an application, we study the latest $n_f=2+1$ LQCD data on the ground-state octet baryon masses from the PACS-CS, QCDSF-UKQCD, HSC, and NPLQCD Collaborations. It is shown that the discretization effects for the studied LQCD simulations are at the order of one to two percent for lattice spacings up to $0.15$ fm and the pion mass up to 500 MeV.

BARYONS: EXTRACTING INFORMATION ON STRUCTURE FROM DATA

A new era of physical insight and understanding on the N*s and their electrocouplings became possible by electron beam facilities and large acceptance detectors, as for example, at JLab. We address issues such as how the new experimental results elucidate us on the strong interaction dynamics in the non-perturbative regime, and what is the possible role of models, and their connection to LQCD data.

Nucleon mass and pion-nucleon sigma term from a chiral analysis of lattice QCD data

The pion-mass dependence of the nucleon mass within the covariant SU(2) baryon chiral perturbation theory both without and with explicit Delta(1232) degrees of freedom up to order p^4 is investigated. By fitting to lattice QCD data in 2 and 2+1 flavors from several collaborations, for pion masses M_pi < 420 MeV, we obtain low energy constants of natural size and compatible with pion nucleon scattering data. Our results are consistent with the rather linear pion-mass dependence showed by lattice QCD. In the 2 flavor case we have also performed simultaneous fits to the nucleon mass and pion-nucleon sigma-term data. As a result of our analysis, which encompasses the study of finite volume corrections and discretization effects, we report a value for the pion-nucleon sigma-term of 41(5)(4) MeV in the 2 flavor case and 52(3)(8) MeV for 2+1 flavors, where the inclusion of the Delta(1232) resonance changes the results by around 9 MeV. In the 2 flavor case we are able to set independently the scale for lQCD data, given by a Sommer scale of r_0=0.493(23) fm.