Lattice QCD is used to calculate the potential between a static quark and anti-quark in the presence of a finite density of pi^+'s. Correlation functions of multiple pi^+'s are used in conjunction with Wilson-loop correlators to determine the difference between the Q\overline{Q}-potential in free-space and in the presence of a pion condensate. The modifications to the potential are found to have significant dependence on the Q\overline{Q} separation over the range r < 1 fm explored in this work. Our results are consistent with the pion-condensate behaving as a (nonlinear) chromo-dielectric.
We incorporate the effective restoration of $U(1)_{\rm A}$ symmetry in the 2+1 flavor entanglement Polyakov-loop extended Nambu--Jona-Lasinio (EPNJL) model by introducing a temperature-dependent strength $K(T)$ to the Kobayashi-Maskawa-'t Hooft (KMT) determinant interaction. $T$ dependence of $K(T)$ is well determined from pion and $a_0$-meson screening masses obtained by lattice QCD (LQCD) simulations with improved p4 staggered fermions. The strength is strongly suppressed in the vicinity of the pseudocritical temperature of chiral transition. The EPNJL model with the $K(T)$ well reproduces m…
We investigate the real and imaginary chemical-potential dependence of pion and $ρ$-meson screening masses in both the confinement and the deconfinement region by using two-flavor lattice QCD. The spatial meson correlators are calculated in the imaginary chemical potential region with lattice QCD simulations. We extract pion and $ρ$-meson screening masses from the correlators. The obtained meson screening masses are extrapolated to the real chemical potential region by assuming some analytic function. In the real chemical potential region, the resulting pion and $ρ$-meson screening masses mono…
We review lattice studies of the color screening in the quark-gluon plasma. We put the phenomena related to the color screening into the context of similar aspects of other physical systems (electromagnetic plasma or cold nuclear matter). We discuss the onset of the color screening and its signature and significance in the QCD transition region, and elucidate at which temperature and to which extent the weak-coupling picture based on hard thermal loop expansion, potential nonrelativistic QCD, or dimensionally-reduced QCD quantitatively captures the key properties of the color screening. We dis…
We use gauge/string duality to estimate the Debye screening mass at non-zero temperature and baryon chemical potential. We interpret this mass as the smallest one in the open string channel. Comparisons are made with the results from holography and lattice QCD.
Temperature dependence of pion and sigma-meson screening masses is evaluated by the Polyakov-loop extended Nambu--Jona-Lasinio model with the entanglement vertex (EPNJL model). We propose a practical way of calculating meson screening masses in the NJL-type effective models. The method based on the Pauli-Villars regularization solves the well-known difficulty that the evaluation of screening masses is not easy in the NJL-type effective models. The method is applied to analyze temperature dependence of pion screening masses calculated with state-of-the-art lattice simulations with success in re…
Temperature dependence of pion and sigma-meson screening masses is evaluated by the Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model with the entanglement vertex. We propose a practical way of calculating meson screening masses in the NJL-type effective models. The method based on the Pauli-Villars regularization solves the well-known difficulty that the evaluaton of screening masses is not easy in the NJL-type effective models.The PNJL model with the entanglement vertex and the Pauli-Villars regularization well reproduces lattice QCD results on temperature dependence of the chiral cond…
We study correlation functions of spatially separated static quark-antiquark pairs in (2+1)-flavor QCD in order to investigate onset and nature of color screening at high temperatures. We perform lattice calculations in a wide temperature range, $140 \le T \le 5814\,{\rm MeV}$, using the highly improved staggered quark action and several lattice spacings to control discretization effects. By comparing at high temperatures our lattice results to weak-coupling calculations as well as to the zero temperature result for the energy of a static quark-antiquark pair, we observe that color screening s…
Colorelectric and Colormagnetic structure of the flux tubes, connecting heavy quark and antiquark, is investigated in the framework of the Field Correlator method which describes all resulting fields in terms of correlators $D^E$ and $D^E_1$. The latter have been computed via gluelumps, which allows to predict the resulting distribution of color fields $\mathbf{E} (\mathbf{r}),$ and colormagnetic currents $\mathbf{k} (\mathbf{r})$ in the flux tubes. It is shown, that at large distances $r\gg λ\approx 0.2$ fm the whole structure of fields and relations between them is similar to that of the dua…
We compute---at finite quark chemical potentials---the color screening of cold quark matter at the one-loop level, comparing the normal, BCS-paired U(1)em (or Higgs) phase and a singlet phase with color-singlet condensate near the Fermi surface. The latter phase is computed using the example of two-color QCD with a color-singlet diquark condensate. In contrast to the normal and Higgs phases, neither electric nor magnetic screening masses appear in the singlet phase. The absence of a magnetic mass, within a perturbative framework, is a consequence of the proper treatment of gauge invariance. Wh…
In this work, we investigate not only the pole masses but also the screening masses of neutral pions at finite temperature and magnetic field by utilizing the random phase approximation (RPA) approach in the framework of the two-flavor Nambu--Jona-Lasinio (NJL) model. And two equivalent formalisms in the presence of a magnetic field, i.e. the Landau level representation (LLR) and the proper-time representation (PTR), are applied to obtain the corresponding analytical expressions of the polarization functions (except the expressions for the pole masses in the PTR). In order to evaluate the appl…
We present some recent results obtained in the study of the color magnetic and electric screening masses in the QCD plasma. In particular, we discuss how the masses get modified by strong external fields which are expected to be created in physical situations such as heavy-ion collisions.
We study correlation functions of spatially separated static quark-antiquark pairs in $2+1$ flavor QCD in order to investigate the nature of color screening at high temperatures. We perform lattice calculations in a wide temperature range, $116~\text{MeV} \leq T \leq 5814~\text{MeV}$, using the highly improved staggered quark (HISQ) action and several lattice spacings to control discretization effects. We alleviate the UV noise problem through the use of four dimensional hypercubic (HYP) smearing, which enables the reconstruction of correlators and determination of screening properties even at…
We study Landau gauge gluon propagators in two-color QCD at finite quark chemical potential ($μ_q$) and temperature ($T$). We include medium polarization effects at one-loop by quarks into massive gluon propagators, and compared the analytic results with the available lattice data. We particularly focus on the high density phase of color-singlet diquark condensates whose critical temperature is $\sim 100$ MeV with weak dependence on $μ_q$. At zero temperature the color singlet condensates protect the IR limit of electric and magnetic gluon propagators from the medium screening effects. At fini…
We present results for the (color)magnetic and (color)electric screening masses of the Quark-Gluon Plasma in the presence of an external magnetic field. The screening masses are extracted from the correlators of Polyakov loops, determined by lattice QCD simulations at the physical point. We explore temperatures in the range $200\,\mathrm{MeV}\lesssim T\lesssim 330\,\mathrm{MeV}$ and magnetic field intensities up to $|e|B \sim 1.3\,\mathrm{GeV}^2$. We find that both screening masses are increasing functions of the magnetic field and that the dependence on $B$ becomes weaker for larger temperatu…
We investigate chemical-potential (μ) dependence of static-quark free energies in both the real and imaginary μregions, performing lattice QCD simulations at imaginary μand extrapolating the results to the real μregion with analytic continuation. Lattice QCD calculations are done on a 16^{3}\times 4 lattice with the clover-improved two-flavor Wilson fermion action and the renormalization-group improved Iwasaki gauge action. Static-quark potential is evaluated from the Polyakov-loop correlation functions in the deconfinement phase. As the analytic continuation, the potential calculated at imagi…
We investigate the properties of the pion quasiparticle in the low-temperature phase of two-flavor QCD on the lattice with support from chiral effective theory. We find that the pion quasiparticle mass is significantly reduced compared to its value in the vacuum, by contrast with the static screening mass, which increases with temperature. By a simple argument, near the chiral limit the two masses are expected to determine the quasiparticle dispersion relation. Analyzing two-point functions of the axial charge density at non-vanishing spatial momentum, we find that the predicted dispersion rel…
Recently, an approximate $SU(4)$ chiral spin-flavour symmetry was observed in multiplet patterns of QCD meson correlation functions, in a temperature range above the chiral crossover. This symmetry is larger than the chiral symmetry of massless QCD, and can only arise effectively when colour-electric quark-gluon interactions dynamically dominate the quantum effective action. At temperatures about three times the crossover temperature, these patterns disappear again, indicating the screening of colour-electric interactions, and the expected chiral symmetry is recovered. In this contribution we …
We investigate the properties of the pion quasiparticle in the low-temperature phase of two-flavor QCD on the lattice with support from chiral effective theory. We find that the pion quasiparticle mass is significantly reduced compared to its value in the vacuum, in contrast to the static screening mass, which increases with temperature. By a simple argument, the two masses are expected to determine the quasiparticle dispersion relation near the chiral limit. Analyzing two-point functions of the axial charge density at non-vanishing spatial momentum, we find that the predicted dispersion relat…
We present lattice QCD results for mesonic screening masses in the temperature range 140 MeV $\lesssim T \lesssim$ 2500 MeV. Our calculations were carried out using (2+1)-flavors of the Highly Improved Staggered Quark (HISQ) action, with a physical value for the strange quark mass and two values of the light quark mass corresponding to pion masses of 160 MeV and 140 MeV. Continuum-extrapolated results were obtained using calculations with a variety of lattice spacings corresponding to temporal lattice extents $N_τ= 6 - 16$. We discuss the implications of these results for the effective restora…
We investigate hadron spectra in 2-color QCD using lattice simulation with $N_{f}=2$ at low temperature and finite density in which there appears not only the hadronic phase but also the superfluid phase. We first calculate the pion and rho meson spectrum, which is well-known from previous works. The spectral ordering of these mesons flips around the quark chemical potential $μ=m^{0}_π/2$ ($m^{0}_π$: the pion mass at $μ=0$), where the phase transition between the hadronic and superfluid phases occurs. For $μ\gtrsim m^{0}_π/2$, the effective mass for the pion linearly increases while the one fo…
In this paper we study the interactions among a static quark-antiquark pair in the presence of dense two-color quark matter with lattice simulation. To this end we compute Polyakov line correlation functions and determine the renormalized color averaged, color singlet and color triplet grand potentials. The color singlet grand potential allows us to elucidate the number of quarks induced by a static quark antiquark source, as well as the internal energy of such a pair in dense quark matter. We furthermore determine the screening length, which in the confinement phase is synonymous with the str…
With the aim of clarification of color correlations among quarks, we investigate the color correlation between a static quark and an antiquark (static $q\bar q$) below and above the phase transition temperature $T_c$ through the entanglement entropy(EE). By a quenched lattice QCD calculation on an anisotropic lattice adopting the standard Wilson gauge action in the Coulomb gauge, we compute a reduced density matrix $ρ$ defined in the color space, and the entanglement entropy $S_{\rm EE}$ constructed from $ρ$. The spatial volume is $L^3 = 24^3$ and the temporal extents are $N_T = 12,13,14,15,16…
Lattice measurements provide adequate information to fix the parameters of long distance effective field theories in Euclidean time. Using such a theory, we examine the analytic continuation of long distance correlation functions of composite operators at finite temperature from Euclidean to Minkowski space time. There are two definitions of mass in each regime; in Euclidean these are the screening and pole masses. The analytic continuation of these mass parameters to real time is non-trivial. This is in contrast to the situation at zero temperature.
We compute the Coulomb interaction energy of dense sets of static quarks in a compact volume (much smaller than the lattice volume) containing one quark per lattice site. The quark color charges are combined into either a set of three-quark nucleon states, or into a non-factorizable "one big hadron" state. In both cases we find that the energy per quark is roughly constant as the volume of quarks increases. A surprise is that if we construct the nucleon states from sets of three quarks chosen at random in the volume, then the energy per quark remains roughly constant, even as the average dista…
Fermions obstruct dimensional reduction in hot QCD
本文首次研究了在1.5Tc < T <3Tc（T_c为手征跃迁发生的温度）范围内，由四种夸克轻动力学味的量子色动力学类胶球凝聚子得到的屏蔽质量。我们还研究了类π介子和类σ屏蔽质量，发现它们在整个T范围内都是简并的。这些阻碍微扰降维，因为最低的胶球屏蔽质量比它们重。我们的结果外推表明，这种阻碍可能会影响整个温度范围内预期达到甚至在大型强子对撞机。
We investigate screening masses at both sides of the first order finite temperature transition with 3 quark flavors using the nonperturbatively improved clover fermion action and the Iwasaki gauge action. We have developed the method of hierarchical truncations with stochastic probing to accelerate the noise estimator for evaluating quark loops at every spatial lattice slices. At parameter values we study, the flavor singlet scalar meson has a screening mass about half of the pion screening mass. It becomes lighter as the system approaches the critical endpoint.
When the center matters: color screening and gluelumps in dihedral lattice gauge theories
ICFO - Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology（ICFO-光子科学研究所，巴塞罗那科技研究所）；Pitaevskii BEC Center, CNR-INO and Dipartimento di Fisica, Università di Trento（皮塔耶夫斯基玻色-爱因斯坦凝聚中心，意大利国家研究委员会光学研究所和特伦托大学物理系）；INFN-TIFPA, Trento Institute for Fundamental Physics and Applications（意大利核物理研究所-特伦托基础物理与应用研究所）；Honda Research Institute Europe GmbH（本田欧洲研究院有限公司）；Dipartimento di Fisica, Università di Pisa, and INFN, Sezione di Pisa（比萨大学物理系和意大利核物理研究所比萨分部）；Dipartimento di Fisica e Astronomia “G. Galilei” and Padua Quantum Technologies Research Center, Universit‘a di Padova（帕多瓦大学伽利略物理与天文系和帕多瓦量子技术中心）；Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova（意大利国家核物理研究所帕多瓦分部）
