Donald Sinclair
(Argonne National Laboratory)

7/23/18, 2:00 PM

Nonzero Temperature and Density

We are applying complex-Langevin simulations to lattice QCD at finite
quark-number chemical potential $\mu$ and zero temperature. While we observe
some improvement as we move to weaker coupling we only find agreement with the
expected physics at very small and at large $\mu$. It has been observed by
others that at least part of the problem is that at small and even zero $\mu$
the gauge...

Dr
Shoichiro Tsutsui
(High Energy Accelerator Research Organization)

7/23/18, 2:20 PM

Nonzero Temperature and Density

Exploring the phase diagram of QCD at finite density is a challenging problem since first-principle calculations based on standard Monte Carlo methods suffer from the sign problem. As a promising approach to this issue, the complex Langevin method (CLM) has been pursued
intensively.
In this talk, we investigate the applicability of the CLM in the vicinity of the deconfinement phase...

Dr
Felipe Attanasio
(University of Washington)

7/23/18, 2:40 PM

Nonzero Temperature and Density

We present results of our technique of dynamic stabilisation (DS) applied to complex Langevin simulations of QCD in the heavy-dense limit and with staggered quarks. We show that DS is able to keep simulations stable, providing results compatible with Monte-Carlo simulations, where the latter is applicable.

Dr
Yuta Ito
(KEK)

7/23/18, 3:00 PM

Nonzero Temperature and Density

Monte Carlo studies of QCD at finite density suffer from
the notorious sign problem, which becomes easily uncontrollable
as the chemical potential increases for a moderate lattice size.
In this work, we attempt to approach the high density
low temperature region by the complex Langevin method (CLM).
Simulations are performed on an 8^3 x 16 lattice using four-flavor
staggered fermions...

18.
Investigating the Phase Structure of Large N Unitary Matrix Models using Complex Langevin Method

Dr
Anosh Joseph
(ICTS-TIFR)

7/23/18, 3:20 PM

Nonzero Temperature and Density

Using complex Langevin method we examine the phase structure of complex unitary matrix models and compare the numerical results with analytic results found at large number of colors. The actions we consider are manifestly complex, and thus the dominant contributions to the path integral comes from the space of complexified gauge field configurations. For this reason, the eigenvalues of unitary...

Kevin Zambello
(University of Parma and INFN)

7/23/18, 4:10 PM

Nonzero Temperature and Density

At finite density, lattice simulations are hindered by the well-known sign problem: for finite chemical potentials, the QCD action becomes complex and the Boltzmann weight e^-S
cannot be interpreted as a probability distribution to determine expectation values by Monte Carlo techniques. Different workarounds have been devised to study the QCD phase diagram, but their application is mostly...

Scott Lawrence
(University of Maryland, College Park)

7/23/18, 4:30 PM

Nonzero Temperature and Density

Fermionic field theories at finite density suffer from a sign problem, making lattice calculations exponentially expensive in the volume. This sign problem can be reduced or eliminated by complexifying configuration space, and integrating over a contour deformed from the real plane. We present an algorithm for determining integration contours with reduced sign problems. We give results from...

Neill Warrington
(University of Maryland, College Park)

7/23/18, 4:50 PM

Nonzero Temperature and Density

Systems of fermions at finite density have complex Boltzmann weights which cause the integrand of the path integral to be highly oscillatory. As a result of these oscillations, standard integration methods require exponential precision in the spacetime volume to compute observables. However, deforming the path integration contour to a manifold which approximates a set of Lefschetz Thimbles...

Dr
Henry Lamm
(University of Maryland)

7/23/18, 5:10 PM

Nonzero Temperature and Density

Finite-density calculations in lattice field theory are typically plagued by sign problems. A promising way to ameliorate this issue is the so-called "holomorphic flow" equations that deform the manifold of integration for the path integral to manifolds in the complex space where the sign fluctuations are less dramatic. In this talk, We will discuss some novel features of applying the flow...

Dr
Kei Suzuki
(KEK)

7/24/18, 2:00 PM

Nonzero Temperature and Density

We investigate the axial $U(1)$ symmetry in the phase above the critical temperature in $N_f=2$ lattice QCD, where the ensembles are generated with Mobius domain-wall fermions, and the overlap/domain-wall reweighting is applied. We show the $U(1)_A$ susceptibility extracted from the spectra of the overlap Dirac eigenmodes and discuss its temperature, quark-mass, and spatial volume dependence....

Mr
Lukas Mazur
(Bielefeld University)

7/24/18, 2:20 PM

Nonzero Temperature and Density

The region of the Columbia plot with two light quark flavors is not yet conclusively understood. Non-perturbative effects, e.g. the magnitude of the anomalous U(1) axial symmetry breaking decides on the nature of the phase transition in this region. We report on our study of this region of the Columbia plot using lattice techniques. We use gauge ensembles generated within the Highly Improved...

Yasumichi Aoki
(KEK)

7/24/18, 2:40 PM

Nonzero Temperature and Density

We study the topological charge in $N_f=2$ QCD at finite temperature
using Mobius domain-wall fermions with reweighting to ovelap fermions.
The susceptibility $\chi_t$ of the topological charge is studied
in the high temperature phase with varying quark mass.
Last year, we reported on a strong suppression of the susceptibility,
observed below a certain value of the quark mass on a fixed...

Mr
P. Thomas Jahn
(TU Darmstadt)

7/24/18, 3:00 PM

Nonzero Temperature and Density

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 a new method to circumvent this...

Mr
Rasmus Larsen
(Brookhaven National Laboratory, Nuclear Theory Group)

7/24/18, 3:20 PM

Nonzero Temperature and Density

We report our study on the properties of the topological structures present in the QCD medium just above the chiral crossover transition. We use dynamical domain wall fermion configurations on lattices of size 32^3x8, used earlier in [1] to calculate the crossover transition temperature Tc in QCD, and detect the topological structures through the zero modes of the overlap operator. In...

Prof.
Michael Ogilvie
(Washington University in St. Louis)

7/24/18, 4:10 PM

Nonzero Temperature and Density

Many scalar field theory models with complex actions are invariant under the antilinear ($\mathcal{PT}$) symmetry operation $L^{*}(-\chi)=L(\chi)$. Models in this class include $i \phi^3$, the Bose gas at finite density and Polyakov loop spin models at finite density. This symmetry may be used to obtain a dual representation where weights in the functional integral are real but not...

Hershdeep Singh
(Duke University)

7/24/18, 4:30 PM

Nonzero Temperature and Density

We formulate a world-line approach to study few body physics on a space-time lattice and develop a worm type algorithm to extract the low lying energy levels. We show that our formulation is efficient for studying non-relativistic spin-half fermions with both attractive and repulsive interactions and in the presence of mass imbalance, especially in one spatial dimension. Recently, such systems...

Oliver Orasch
(University of Graz)

7/24/18, 4:50 PM

Nonzero Temperature and Density

We study a complex $\phi^4$ field at finite temperature and finite density using a worldline representation. In particular we focus on the low temperature regime where the particle number shows condensation steps as a function of the chemical potential. The critical values of the chemical potential, i.e., the condensation thresholds, are related to the mass and higher multi-particle energies...

Mr
Patrick Steinbrecher
(Brookhaven National Lab)

7/25/18, 4:10 PM

Nonzero Temperature and Density

We will present new state-of-the-art lattice QCD results on the chiral crossover temperature of QCD for moderately large baryon chemical potential. Firstly, we will present a more precise updated result for the QCD pseudo-critical temperature at zero baryon chemical potential, obtained from all possible second-order chiral susceptibilities that diverge in the chiral limit. Then we will present...

Jana N. Guenther
(University of Regensburg)

7/25/18, 4:30 PM

Nonzero Temperature and Density

When comparing lattice calculation to experimental data from heavy ion collision experiments, the higher order fluctuations of conserved charges are important observables. An efficient way to study these fluctuations is to derive them from simulations at a set of imaginary chemical potentials. In this talk we present results for higher order derivatives with respect to $\mu_B$, $\mu_S$ and...

Mr
Jishnu Goswami
(Bielefeld University)

7/25/18, 4:50 PM

Nonzero Temperature and Density

The QCD phase diagram at finite temperature and density has a very rich physical structure which can be explored with first principle lattice QCD calculations. We study the QCD phase diagram of (2+1)-flavor QCD with imaginary chemical potential using HISQ action which has reduced taste breaking effects compared to the unimproved staggered quark action and hence may allow us to get close to the...

Dr
Akio Tomiya
(Central China Normal University)

7/25/18, 5:10 PM

Nonzero Temperature and Density

We study the phase structure of QCD with three degenerate flavors in external magnetic fields using HISQ fermions. The simulations are performed on $16^3\times6$ and $24^3\times6$ lattices. In order to investigate the quark mass dependence of the QCD transition we vary the values of quark masses from 0.015 to 0.0009375 corresponding to $m_\pi=320$ MeV and $80$ MeV in the continuum limit. We...

Mr
Mizuki Shirogane
(Niigata University)

7/26/18, 8:30 AM

Nonzero Temperature and Density

Parallel

We study energy gap (latent heat) between the hot and cold phases at the first order phase transition point of the SU(3) gauge theory. Performing simulations on lattices with various spatial volumes and lattice spacings, we calculate the energy gap by a method using the Yang-Mills gradient flow and compare it with that by the conventional derivative method.

Dr
Johannes Heinrich Weber
(Michigan State University)

7/26/18, 8:50 AM

Nonzero Temperature and Density

We calculate the equation of state at high temperatures in 2+1 flavor QCD using the highly improved staggered quark (HISQ) action. We study the lattice spacing dependence of the pressure at high temperatures using lattices with temporal extent (N_\tau= 6,\ 8,\ 10) and (12) and perform continuum extrapolations.
We also give a continuum estimate for the equation of state up to temperatures (T =...

Prof.
Yusuke Taniguchi
(University of Tsukuba)

7/26/18, 9:10 AM

Nonzero Temperature and Density

We study correlation functions of the energy-momentum (EM) tensor in Nf=2+1 full QCD for the sake of QGP viscosities.
The viscosity is given by three steps on lattice:
(1) calculate two point correlation functions of the energy-momentum tensor,
(2) derive the spectral function from the correlation function,
(3) applying the Kubo's formula the viscosity is related to the spectral...

Mr
Takehiro Hirakida
(Kyushu University)

7/26/18, 9:30 AM

Nonzero Temperature and Density

We present lattice calculations of the equation of state of pure SU(2) gauge theory by using the gradient flow. The scale-setting of lattice parameter has been carried, and we propose a reference scale t0 satisfying t2E=0.1 for SU(2) gauge theory. This reference value is fixed by a natural scaling-down of the t0 scale for the SU(3) based on perturbative analysis. We also show the thermodynamic...

Etsuko Itou
(RCNP, Osaka University/Kouchi University)

7/26/18, 9:50 AM

Nonzero Temperature and Density

We study two-color QCD with nonzero chemical potential using Iwasaki gauge and Wilson fermion action.
The two-color gauge theory coupled to an even number of fundamental fermions does not suffer from the sign problem because the fermion transforms in a real representation.
To perform the simulation even in high chemical potential regime, as in earlier publications, we introduce a diquark...

Mr
Amit Kumar
(Wayne State University)

7/26/18, 10:10 AM

Nonzero Temperature and Density

The jet transport coefficient $\hat{q}$ is the leading parameter that controls the modification of hard jets produced in heavy-ion collisions. This coefficient, like other jet coefficients is inherently non-perturbative, and hence, is challenging to compute from first principles. Currently, existing theoretical model to data comparisons require a separate normalization of $\hat{q}$ between...

Dr
Francesca Cuteri
(J. W. Goethe Universität)

7/26/18, 11:00 AM

Nonzero Temperature and Density

We investigate to which extent we can exploit the dependence of the order of the chiral transition on the number of light degenerate flavors $N_\text{f}$, re-interpreted as continuous parameter in the path integral formulation, as a means to perform a controlled chiral extrapolation and deduce the order of the transition for the case $N_\text{f}=2$, which is still under debate.

Mr
Sheng-Tai Li
(Central China Normal University)

7/26/18, 11:20 AM

Nonzero Temperature and Density

The chiral phase transition temperature $T_{c}$ is a fundamental quantity of QCD. To determine this quantity, we have performed simulations of (2 + 1)-flavor QCD using the Highly Improved Staggered Quarks (HISQ) action on $N_{\tau}=6, 8, 12$ lattices and aspect ratios $N_{\sigma}/N_{\tau}$ ranging from 4 to 7.
In our simulations, we fix the strange quark mass value to its physical value...

Dr
Gergely Endrodi
(Goethe University Frankfurt)

7/26/18, 11:40 AM

Nonzero Temperature and Density

We investigate the properties of the finite-temperature
QCD transition towards the chiral limit using staggered
quarks. Starting from the 2+1 flavor physical point, the
limit of massless quarks is approached along two different
trajectories in the Columbia-plot. Unlike in previous
approaches, the chiral condensate is determined via the
Banks-Casher relation. The first results of...

Mr
Atsushi Baba
(University of Tsukuba)

7/26/18, 12:00 PM

Nonzero Temperature and Density

In the lattice gauge theory with Wilson fermion, chiral symmetry is explicitly broken. A non-trivial additive correction is needed to renormalize the chiral condensate. In this study, we use gradient flow to avoid this problem. Gradient flow makes us possible to define correctly renormalized chiral susceptibility without additive renormalization.
We measure not only disconnected diagram but...

Dr
Hiroshi Ohno
(University of Tsukuba)

7/26/18, 12:20 PM

Nonzero Temperature and Density

We report our updated study on the critical endpoint of the finite temperature phase transition in 4-flavor QCD with Wilson-Clover fermions. Using the kurtosis intersection method, we determined the critical endpoint on lattices with $N_t$ = 4, 6 and 8. Our continuum extrapolated result shows that the critical pion mass is clearly larger compared to one in 3-flavor, which suggests that the...

Daniel Hackett
(University of Colorado Boulder)

7/26/18, 12:40 PM

Nonzero Temperature and Density

To date, studies of the thermodynamics of QCD in the limit of large number of colors have been limited to the quenched approximation, i.e., the behavior of pure SU(N) gauge theory at large N. We present a progress report on our investigation of the phase structure of large-N QCD in the presence of (Wilson) fermions with finite mass. We explore the light quark mass regime by simulating with two...

Dr
Michael Wagman
(MIT)

7/27/18, 2:00 PM

Nonzero Temperature and Density

Correlation functions for baryons, or generically systems with different U(1) charges than the vacuum, have phase fluctuations that lead to sign problems obstructing studies of finite-density matter using correlation functions. I will discuss phase fluctuations in lattice QCD and in a one-dimensional complex scalar field toy model and methods to exploit the structure of phase fluctuations to...

Mr
Gurtej Kanwar
(MIT)

7/27/18, 2:20 PM

Nonzero Temperature and Density

Lattice QCD estimates of correlation functions with non-zero U(1) baryon number suffer from a well known signal-to-noise problem at large time separations. Previous work has shown that this can be attributed to a widening phase distribution over a circular domain, where standard estimators perform exponentially poorly as the distribution approaches uniform. We present a new approach to this...

Prof.
Benjamin Jaeger
(CP3 & DIAS, University of Southern Denmark)

7/27/18, 2:40 PM

Nonzero Temperature and Density

The QCD pressure at non-zero chemical potential mu is typically obtained
via a Taylor expansion in mu. The Taylor coefficients are traces of
powers of the inverse Dirac matrices, which are computed using many noisy
estimators. Here, we present an alternative based on the Cauchy Residue Theorem and discuss its merits for the Taylor coefficients.

Dr
Bingnan Lu
(Michigan State University)

7/27/18, 3:00 PM

Nonzero Temperature and Density

We present the first ab initio calculations of nuclei and nuclear matter at finite temperature. Using lattice Monte Carlo simulations and chiral effective field theory, we probe the thermal properties of nuclear systems from first principles. We find that the pinhole algorithm, initially developed for extracting nucleon densities, is well suited for computing the canonical partition function....

Mr
Lukas Holicki
(JLU Giessen)

7/27/18, 3:20 PM

Nonzero Temperature and Density

Chiral Random Matrix Theory has proven to describe the spectral prop-
erties of low temperature QCD very well. However, at temperatures above
the chiral symmetry restoring transition it can not provide a global descrip-
tion. The level-spacing distribution in lower part of the spectrum of the
Dirac operator is Poisson-like. The eigenmodes are localized in space-time
and separated from the...

Dr
Unger Wolfgang
(Bielefeld University)

7/27/18, 4:30 PM

Nonzero Temperature and Density

Lattice QCD at strong coupling has long been studied in a dual representation to circumvent the finite baryon density sign problem. Recent results that established the non-perturbative functional dependence between the bare anisotropy and the physical anisotropy a/a_t in the chiral limit are now extended to finite quark mass. We discuss the consequences of the anisotropy callibration to the...

Mr
Marc Klegrewe
(Bielefeld University)

7/27/18, 4:50 PM

Nonzero Temperature and Density

We present results for lattice QCD in the limit of infinite gauge coupling on a discrete spatial but continuous Euclidean time lattice. A worm type Monte Carlo algorithm is applied in order to sample two-point functions which gives access to the measurement of mesonic temporal correlators. The continuous time limit, based on sending Nτ→∞ and the bare anistotropy to infinity while fixing the...

Dr
Jonas Glesaaen
(Swansea University)

7/27/18, 5:10 PM

Nonzero Temperature and Density

Although the general behaviour of the crossover of QCD into the quark-gluon plasma phase at zero chemical potential is fairly well understood, the question of what exactly happens to the bound states of the theory in the crossover region is still not fully answered. In this talk the continuation of the FASTSUM collaboration's investigation of hadrons in the region of $T_c$ will be presented....

Prof.
Heng-Tong Ding
(Central China Normal University)

7/27/18, 5:30 PM

Nonzero Temperature and Density

The spectral function is the key for understanding the in-medium hadron properties as well as the transport properties of the medium.
Such as the dissociation temperatures of quarkonia, diffusion coefficients, dilepton emission rates as well as viscosities can be read-off
from various corresponding spectral functions. As well-known that the spectral function is hidden in the...

Mr
Christian Rohrhofer
(University of Graz)

7/27/18, 5:50 PM

Nonzero Temperature and Density

We report on the progress of understanding spatial correlation functions
in high temperature QCD. We study isovector meson operators in Nf=2 QCD
using domain-wall fermions on lattices of Ns=32 and different quark
masses. It has previously been found that at $\sim 2 T_c$ these observables
are not only chirally symmetric but in addition approximately
$SU(2)_{CS}$ and $SU(4)$ symmetric. In...