Conveners
QCD at non-zero density: TR5
- Jishnu Goswami (RIKEN Center for Computational Science)
QCD at non-zero density: TR5
- Bastian Brandt (University of Bielefeld)
QCD at non-zero density: TR5
- Etsuko Itou (YITP, Kyoto U.)
QCD at non-zero density: TR4
- Gergely Endrodi (Bielefeld University)
QCD at non-zero density: TR5
- Shinji Ejiri (Niigata University)
If there is a first-order phase transition in the light quark region of 2+1 flavor finite temperature and density QCD and if the region of the first-order phase transition expands with increasing density as suggested by several lattice studies, then, at very high densities, we may expect that the first-order phase transition region expands into the heavy quark region of QCD, where we can...
The crossover from hadronic to quark matter is understood to be both a deconfinement as well as a chiral symmetry restoring transition. Here, we study observables related to both aspects using lattice simulations: the Polyakov loop and its derivatives and the chiral condensate and its derivatives. At zero baryochemical potential, and infinite volume, the chiral and deconfinement crossover...
The nature of the QCD phase transition in the chiral limit constitutes a challenging problem for lattice QCD as it is not directly simulable. Its study, however, provides constraints on the phase diagram at the physical point. Recently, the thermal transition for massless fermions was shown to be of second order for all numbers of flavours $N_f \lesssim 7$. For this, the lattice chiral limit...
We investigate the thermodynamics and phase structure of SU(3) Yang-Mills theory on $T^2\times R^2$ with anisotropic spatial volumes in Euclidean spacetime in lattice numerical simulations and an effective model. In lattice simulations, the energy-momentum tensor defined through the gradient flow is used for the analysis of the stress tensor on the lattice. It is found that a clear pressure...
We revisit QCD with three mass-degenerate quark flavors at an imaginary isospin chemical potential set to 4pi/3. This choice corresponds to a special point in the parameter space, where the theory possesses an exact Z(3) center symmetry. Through a finite-size scaling analysis, we demonstrate that in this case the finite temperature QCD transition is of first order and entails singular behavior...
The order of the thermal chiral phase transition in lattice QCD is strongly cutoff-dependent. A recent study from our group using mass-degenerate, unimproved staggered quarks on $N_\tau=\{4,6,8\}$ lattices found that the first-order regions shrink to zero for $N_\text{f}\in[2,6]$ as the continuum limit is approached for zero chemical potential. Here we present the progress of an analogous...
Finite density and strong magnetic fields are expected in peripheral heavy-ion collision experiments. Moreover, global strangeness-neutrality is an important condition satisfied by the system. Therefore, in this work, we study the impact of magnetic fields on the equation of state of dense QCD in the line of strangeness-neutrality and isospin asymmetry from lattice QCD simulations at imaginary...
Equilibrium properties of strongly interacting matter are typically characterized by the quantum chromodynamics (QCD) equation of state (EoS). External factors, especially magnetic fields that reach the order of the QCD scale, can significantly influence this characterization. Strong magnetic fields can be produced in the relativistic heavy-ion collisions where baryon chemical potentials can...
In this work we discuss our results on the Roberge-Weiss (RW) transition at imaginary chemical potentials and in the presence of background magnetic fields. We perform lattice QCD simulations on $N_t=6,8$ lattices with $2$+$1$ flavors of stout-staggered fermions at physical quark masses and the tree-level Symanzik improved gauge action. We determine the location the RW endpoint at finite...
We have shown by lattice QED simulations that an external magnetic field
induces chiral symmetry breaking with a non-zero chiral condensate, as predicted
by Schwinger-Dyson methods, using a single large external magnetic field
(see J.B.Kogut and D.K.Sinclair, Phys. Rev. D 109, 034511 (2024)). We
are now extending these simulations to a weaker magnetic field to test that
the chiral...
For the exploration of the phase diagram of finite density QCD, effective Polyakov loop theories derived from lattice QCD provide a valuable tool in the large quark mass regime. Using mean field approximations these theories are evaluated in the high and low temperature regimes at finite baryon chemical potential. The resulting phase diagram is discussed.
For non-zero chemical potential, the sign problem prohibits the simulation of lattice QCD using traditional Monte-Carlo methods. I will present a tensor-network approach based on singular value decomposition to compute the partition function and thermodynamic observables of two-dimensional lattice QCD in the strong-coupling expansion for general orders of the coupling parameter β....
Simulating full QCD for non-zero chemical potential introduces a sign-problem, which we here circumvent using the Complex Langevin method. At lower temperatures, the simulations are unstable, therefore the dynamical stabilization was proposed, which is a soft cutoff in imaginary directions of the complexified field manifold. Before simulating full QCD, we look at a simpler toy-model to study...
The strong coupling expansion for staggered fermions allows for Monte Carlo simulations using a dual representation. It has a mild sign problem for low values of the inverse gauge coupling $\beta$ , hence the phase diagram in the full $\mu_B$ - $T$ plane can be evaluated. We have extended this framework to include $O(\beta^2)$ corrections, by mapping the degrees of freedom to a vertex model....
We extend our measurement of the equation of state of isospin asymmetric QCD to small baryon and strangeness chemical potentials, using the leading order Taylor expansion coefficients computed directly at non-zero isospin chemical potentials. The challenging extrapolations of the fully connected contributions to vanishing pion source are facilitated by using information from isospin chemical...
We investigate the phase structure and the equation of state (EoS) for dense two-color QCD (QC2D) at low temperature (T=40 MeV, $32^4$ lattice) for the purpose of extending our previous works at T=80 MeV ($16^4$ lattice). Indeed, a rich phase structure below the pseudo-critical temperature Tc as a function of quark chemical potential μ has been revealed, but finite volume effects in a...
We present recent updates and results from two-colour lattice QCD simulations at non-zero baryon density, including progress toward determining the speed of sound.
Lattice QCD calculations of many-meson systems at multiple volumes and lattice spacings and at quark masses above and below the physical values are used to compute the QCD equation of state for isospin-dense matter over a wide range of isospin chemical potentials at zero temperature. Agreement is seen with chiral perturbation theory predictions for small chemical potentials and comparison to...
In contrast to the case of non-zero baryon chemical potential, the isospin chemical potential does not introduce a sign problem and can be simulated on the lattice. When the isospin chemical potential is large enough, a phase transition to a Bose-Einstein condensate of pions takes place. Currently available results in the literature on the phase diagram and the equation of state in this setup...
We report on the results of the 2+1 flavour QCD simulations at nonzero isospin chemical potential performed at half the physical light quark mass. At low temperatures and large isospin chemical potential Bose-Einstein Condensation (BEC) occurs, creating a pion condensed phase, separated from the hadronic and quark-gluon plasma phases by the BEC transition line. We show that for lighter than...
We explore the phase diagram of (2+1)-flavour QCD through the fluctuations of conserved charges calculated with Möbius domain-wall Fermions (MDWF). We present quark number susceptibilities and conserved charge fluctuations at pion masses around 220 MeV and 135 MeV for aspect ratios of lattices LT=2 and LT=3, respectively. Results are compared with the previous works by the previous works by...
Fluctuations play a key role in the study of QCD phases. Lattice QCD is a valuable tool to calculate them, but going to high orders is challenging. Up to the fourth order, continuum results are available since 2015. We present the first continuum results for sixth order baryon fluctuations for temperatures between $T=130−200$ MeV, and eighth order at $T=145$ MeV in a fixed volume. We show that...
Taylor expansion at $\mu=0$ and computations at imaginary values of the chemical potential are the two most popular approaches to tackle the sign problem in finite-density lattice QCD. The two methods are obviously related. In particular, the Taylor coefficients are often reconstructed from the data obtained at imaginary $\mu$.
In the context of the Bielefeld-Parma collaboration, we have been...
We propose a general procedure to use the finite-size scaling of Lee-Yang zeros (LYZ) for investigating critical points (CP). This method makes use of the multiple LYZ obtained on finite-volume simulations for determining the properties of the CP, such as the location, universality class, and axes to embed the scaling function.
We apply this method to the analysis of the CP in the 3-state...
Near a critical endpoint the Lee-Yang edge singularity approaches the real axis in the complex chemical potential plane. In the vicinity of the critical point the functional form of this approach depends on the universality class. Assuming a three dimensional Ising critical point in the QCD phase diagram the location of the critical endpoint can be extrapolated provided that the position of...
Imaginary baryon number chemical potential simulations are a popular workaround for the (in)famous sign problem plaguing finite density QCD studies on the lattice. One is necessarily left with the problem of analytically continuing results to real values of $\mu_B$. In the framework of the Bielefeld Parma Collaboration, we have in recent years studied a multi-point Padé description of the net...
