Conveners
Nonzero Temperature and Density
- Owe Philipsen (Goethe-University Frankfurt)
Nonzero Temperature and Density
- Kazuyuki Kanaya (University of Tsukuba)
Nonzero Temperature and Density
- Christian Schmidt (University of Bielefeld)
Nonzero Temperature and Density
- Gert Aarts (Swansea University)
Nonzero Temperature and Density
- Alexander Rothkopf (University of Stavanger)
Nonzero Temperature and Density
- Olaf Kaczmarek (University of Bielefeld)
Nonzero Temperature and Density
- Tamas G. Kovacs (Institute for Nuclear Research, Debrecen)
Nonzero Temperature and Density
- Rajiv Gavai (TIFR)
Nonzero Temperature and Density
- Masakiyo Kitazawa (Osaka University)
Nonzero Temperature and Density
- Prasad Hegde (Indian Institute of Science)
We present a lattice QCD calculation with (2+1)-flavor of highly improved staggered quarks (HISQ). The light quark masses are chosen predominantly lighter than physical, i.e. they correspond to a Goldstone pion mass in the range of 58 MeV < $m_\pi$ < 163 MeV. The strange quark mass is kept at its physical value. We propose two novel estimators for the transition temperate, based on the scaling...
We utilize eigenvalue filtering technique combined with the stochastic estimate of the mode number to determine the low-lying eigenvalue spectrum of the Dirac operator. Simulations are performed with (2 + 1)-flavor QCD using the Highly Improved Staggered Quarks (HISQ/tree) action on $N_{\tau}$ = 8 and 12 lattices with aspect ratios $N_{\sigma}/N_{\tau}$ ranging from 5 to 7. In our simulations...
In quenched QCD the Polyakov loop is an order parameter of the deconfinement transition, but with decreasing quark mass the peak in the Polyakov loop susceptibility becomes less pronounced and it loses its interpretation as an indicator for deconfinement. In this study we examine the dependence of the susceptibility on the light quark mass, following it toward the chiral limit. In particular...
We present results from calculations of conserved charge fluctuations in (2+1)-flavor QCD using light quark masses in the range $m_s/160 \le m_l \le m_s/27$, with the strange quark mass ($m_s$) kept fixed at its physical value. This corresponds to a Goldstone pion mass in the range $55 MeV\le m_\pi \le 140 MeV$. The measurements have been done using HISQ fermion discretization and Symanzik...
We study the endpoint of the first order deconfinement phase transition of two and 2+1 flavor QCD in the heavy quark region. We perform simulations of quenched QCD and apply the reweighting method to study the heavy quark region. The quark determinant for the reweighting is evaluated by a hopping parameter expansion. To reduce the overlap problem, we introduce an external source term of the...
We will present first results of our study of the Euclidean topological charge density correlator.
In order to get a well defined topological charge density and to improve the signal of the correlators at large distances we make use of the gradient flow.
We investigate the flow-time dependence on large and fine quenched lattices and compare to results of 2+1-flavor HISQ lattices. The final...
At high temperatures, the topological susceptibility of QCD becomes relevant for the properties of axion dark matter. However, the strong suppression of non-zero topological sectors causes ordinary sampling techniques to fail, since fluctuations of the topological charge can only be measured reliably if enough tunneling events between sectors occur. We present an improvement of a technique the...
We measure the connected and disconnected mesonic correlators and
screening masses in the high-temperature phase of $N_f=2$ QCD. Gauge
ensembles are generated with Mobius domain-wall fermions, while the
observables are calculated with a reweighting to achieve more precise
chiral symmetry. We confirm the restoration of axial $U(1)$ symmetry for
small quark masses. At a larger quark mass, the...
Properties of QCD matter change significantly around the chiral crossover temperature, and the effects on $U(1)_A$ and topological susceptibilities, as well as the meson spectrum have been studied with much care. Baryons and the effect of parity doubling in this temperature range have been studied perviously by various other groups employing different setups. Here we construct suitable...
Tempered Lefschetz thimble method (TLTM) [Fukuma and Umeda, arXiv:1703.00861] is a (parallel-)tempering algorithm to solve the sign problem in Monte Carlo simulations. It is implemented on the generalized Lefschetz thimble method (GLTM) by using the flow time of the antiholomorphic gradient flow as the tempering parameter. The TLTM is expected to versatilely solve the dilemma between the sign...
Lefschetz thimbles regularisation of (lattice) field theories was put forward as a possible solution to the sign problem. Despite elegant and conceptually simple, it has many subtleties, a major one boiling down to a plain question: how many thimbles should we take into account? In the original formulation, a single thimble dominance hypothesis was put forward: in the thermodynamic limit,...
The complexification of field variables is an elegant approach to attack the sign problem. In one approach one integrates on Lefschetz thimbles: over them, the imaginary part of the action stays constant and can be factored out of the integrals so that on each thimble the sign problem disappears. However, for systems in which more than one thimble contribute one is faced with the challenging...
Lefschetz thimbles have been discussed recently as a possible solution to the complex action problem (sign problem) in Monte Carlo simulations. Here we discuss the structure of Lefschetz thimbles for pure pure Yang-Mills theories with a complex gauge coupling $\beta$ and show how the gauge degrees of freedom alter the thimble decomposition. We propose to simulate such theories on the union of...
In the talk we discuss the sign problem and the possibility to alleviate it with the help of methods related to Lefschetz thimbles in the space of complexities field variables. In particular, we consider two-dimensional Hubbard model at finite density. We analyze the model on the square lattice combining semi-analytical study of saddle points and thimbles on a small lattice and results of test...
The path optimization has been proposed to weaken the sign problem which appears in some field theories such as finite density QCD. In this method, we optimize the integral path in the complex plain to enhance the average phase factor. This method has been applied to a one dimensional integral [1], finite density complex scalar field [2], and the Polyakov loop extended Nambu-Jona-Lasinio model...
We explore the QCD phase diagram at finite density with four-flavor staggered fermions using the complex Langevin method (CLM), which is a promising approach to overcome the sign problem. In our previous work [arXiv:1811.12688] on an $8^3 \times 16$ lattice at $\beta=5.7$ with the quark mass $m=0.01$, we have found that the baryon number density has a clear plateau as a function of the...
We will present current status of our simulations of Lattice QCD at finite baryon-number density using complex Langevin methods, including use of actions enhanced using dimension 6 operators.
Screening masses are useful observables since they provide information regarding the various excitations in the QGP, as well as regarding the restoration of various symmetries. They are also easier to calculate in lattice QCD as compared to temporal correlators. We present results from a high statistics determination of various meson screening correlators for temperatures between approximately...
We examine the analytic continuation of long-distance correlation functions of composite operators at finite temperature from Euclidean to Minkowski. There are two definitions of mass in each regime; in Euclidean these are the screening and pole masses. In a field theoretical model we show that the analytic continuation of these mass parameters is non-trivial and requires short-distance...
We will present our analysis of continuum extrapolated charmonium and bottomonium correlators calculated from very large and fine lattices in the pure SU(3) plasma using clover-improved Wilson valence quarks, extending the study of the pseudo-scalar channel [1].
Two sources of systematic errors may arise in the comparison. On the lattice side, the renormalization constants are not exactly...
In order to study spectral quantities in thermal QCD, the FASTSUM collaboration employs anisotropic lattice simulations with Nf=2+1 flavours of Wilson fermions. Here we discuss our Generation 2 and Generation 2L ensembles, which differ in the pion mass. We focus on observables related to the light quarks and chiral symmetry restoration. Moreover, to prepare for the results to be discussed in...
In order to study the fate of mesons in thermal QCD at finite baryon chemical potential, we consider light mesonic correlation functions using the Taylor expansion to O$\Bigl( (\mu/T)^2 \Bigr)$, in both the hadronic and quark-gluon plasma phases. We use the FASTSUM anisotropic fixed-scale lattices with N$_f$=2+1 flavors of Wilson fermions. We find that mesonic correlators are sensitive to...
We present new results on bottomonium at nonzero temperature, using the FASTSUM Generation 2L ensembles. Preliminary results for spectral function reconstruction using the Maximal Entropy Method and Machine Learning are presented.
Elucidating the production process of heavy quark bound states is a central goal in heavy-ion collisions [1]. Two central questions exist: Do bound states of heavy quarks form in the early time evolution of the glasma? If so, in which time regime can that happen? An answer requires the development of a non-perturbative treatment of the real-time-dynamics of heavy quarkonia.
To answer those...
In this talk we report the progress of our studies on the temporal correlation functions under gradient flow from lattice QCD. The operators to construct the correlation functions under consideration include the energy-momentum tensor and color-electric field. These calculations are the first step in our long-term project of estimating some important quantities: shear&bulk viscosities and...
We report progress towards measuring heavy momentum diffusion coefficient from a correlator of colour electric fields attached to a Polyakov loop in pure SU(3) gauge theory. Using a multilevel algorithm and tree-level improvement, we study the behavior of the diffusion coefficient as a function of temperature in a range 1.5<T/T_c<15 in order to compare it to the perturbative expansions...
We estimate the photon emission rate of the quark-gluon plasma in lattice
QCD. At leading order in the electromagnetic coupling, the photon rate is
proportional to the vector-channel spectral function evaluated on the light
cone. The determination of the spectral function from lattice correlator
data represents an ill-posed problem, which we address by introducing a Padé
ansatz for the...
It has been long and widely believed that topological configurations play crucial roles in the nonperturbative phenomena of QCD and that of Yang-Mills fields in general. Unprecedented amount of high precision data from lattice gauge theories as well as from collider experiments at RHIC and LHC have provided opportunities for nailing down the topological component and characterizing its...
We investigate the order of phase transition in
three flavor QCD with a background $U(1)$ magnetic field using
the standard staggered action with the plaquette gauge action.
We perform simulations for three volumes $N_\sigma = 8,16,24$ with fixed mass $ma=0.030$ and temporal extent $N_\tau=4$, which is expected to show crossover for vanishing magnetic field.
We apply physically same magnitude...
We studied the temporal correlation functions for mesons in different channels in (2+1)-flavor QCD in the presence of external magnetic fields at zero temperature. The simulations were performed on $32^3 \times 96$ lattices using the Highly Improved Staggered Quarks (HISQ) action with $m_{\pi}$ around 230 MeV. The strength of magnetic fields range in $ 0 < |eB| ≲ 3\ \text{GeV}^2$. We found...
In this talk, we will present our study on the chiral magnetic effect in a lattice model. We study analytically the one-loop contribution to the chiral magnetic effect (CME) using lattice regularization with a Wilson fermion field. In the continuum limit, we find that the chiral magnetic current vanishes at nonzero temperature but emerges at zero temperature consistent with that found by...
We study the conductivity of quark-gluon matter in the presence of external magnetic field $B$ within LQCD with dynamical staggered $2 + 1$ quarks at physical pion $m_{\pi}$ and strange quark $m_s$ masses in the deconfinement phase $T = 200\,\mbox{MeV}$. We first measure the current-current Euclidean correlator, then extract the conductivity via analytical continuation within the...
We study the phase diagram of QCD at nonzero temperature, chemical potential and magnetic field. Simulations are performed with $N_f=2+1$ stout improved staggered quarks (with physical masses) and nonzero imaginary chemical potential. Results for real $\mu$ values are obtained by means of analytical continuation. By studying the renormalized chiral condensate and its dependence on the...
We investigate the QCD phase diagram close to the isospin chemical potential axis. Simulations directly along this axis are not hindered by the sign problem and pion condensation can be observed at high enough values of the isospin chemical potential. We study how the related phase boundary evolves in the baryon and strangeness chemical potential directions via reweighting in the quark...
Across the finite temperature transition to the quark-gluon plasma, the QCD
topological susceptibility decreases sharply. Thus in the high temperature
phase the remaining topological objects (possibly calorons) form a weakly
interacting dilute gas. The overlap Dirac operator, through its exact zero
modes, allows one to measure the net topological charge. We show that
separately the number of...
We study thermal phases of QCD via scaling properties of glue fields at long spatial distances. Interesting phase structure emerges.
It is important to compute transport coefficients in QCD at finite temperature and density. When the imaginary-time formalism of Lattice QCD is used, the spectral functions have to be reconstructed by supplementing certain Ansatze for correlation functions on the lattice. On the other hand, real-time Green’s functions can be obtained directly in the Schwinger-Keldysh (SK) formalism. But the SK...
We explore the distribution of the energy momentum tensor (EMT) around quark—anti-quark and single quark at nonzero temperature in SU(3) Yang-Mills gauge theory. This is an extension of our previous study [1] on the EMT distribution in static quark—anti-quark systems in vacuum. We discuss the disappearance of the flux tube structure observed in the vacuum simulation. We investigate the total...
For the phenomenology of quarkonia in quark-gluon plasma, a convenient tool is to define an “in-medium potential”. Formally, such a potential can be defined through the long-time behavior of a timelike Wilson loop.
A non-perturbative estimate of such a potential from lattice QCD is difficult, as on lattice we can only study Wilson loops in Euclidean time, in the range [0, 1/T) where T is the...
We present a new theoretical and practical strategy to renormalize non-perturbatively the energy-momentum tensor in lattice QCD based on the framework of shifted boundary conditions. As a preparatory step for the fully non-perturbative calculation, we apply the strategy at 1 loop in perturbation theory determining the renormalization constants both of the gluonic and of the fermionic...
We investigate the critical endpoints of the finite temperature phase transition of QCD at zero chemical potential. We employ the renormalization-group improved Iwasaki gauge action and non-perturbatively O(a)-improved Wilson-clover fermion action. The critical endpoints are determined by using the intersection point of kurtosis, employing the multi-parameter, multi-ensemble reweighting...
We study thermodynamic properties of 2+1 flavor QCD with improved Wilson quarks applying the method of Makino and Suzuki based on the gradient flow. The method provides us with a general way to compute correctly renormalized physical observables irrespective of explicit violation of symmetries due to the regularization, such as the violation of Poincare and chiral symmetries on the lattice. We...
We report on the computation of the quark propagator at finite temperature in the Landau gauge using quenched gauge configurations. The propagator form factors are computed for various temperatures, above and below the gluon deconfinement temperature $T_c$, and for all the Matsubara frequencies. Our results suggest a strong connection between quark and gluon deconfinement and favour chiral...
We argue the existence of “partially deconfined phase” in some SU(N) gauge theories, that is in between the confined and deconfined phases.
We characterize this phase in terms of the Polyakov line phases and study examples of theories in which the partially deconfined phase exists. We find that this phase is closely related to the Gross-Witten-Wadia phase transition.
The partially deconfined...
The high temperature expansion (HTE) had been widely used as a standard tool to study phase transitions in statistical mechanics. This method applied to QCD effective theories provides new insights to study quark matter at finite chemical potential. In this talk, the general idea of HTE for the Ising model is briefly reviewed and its applications to effective theories of QCD are described. We...
CLE is a well defined method providing a general instrument for ab initio, approximation free studies of realistic lattice models even for complex action. The latter include full QCD at finite densiy and CLE is the only method presently applied in this context. The complexification of the variable space required by a complex action introduces however special conditions to be satisfied in order...
