260 research outputs found
Dynamical stabilisation of complex Langevin simulations of QCD
The ability to describe strongly interacting matter at finite temperature and
baryon density provides the means to determine, for instance, the equation of
state of QCD at non-zero baryon chemical potential. From a theoretical point of
view, direct lattice simulations are hindered by the numerical sign problem,
which prevents the use of traditional methods based on importance sampling.
Despite recent successes, simulations using the complex Langevin method have
been shown to exhibit instabilities, which cause convergence to wrong results.
We introduce and discuss the method of Dynamic Stabilisation (DS), a
modification of the complex Langevin process aimed at solving these
instabilities. We present results of DS being applied to the heavy-dense
approximation of QCD, as well as QCD with staggered fermions at zero chemical
potential and finite chemical potential at high temperature. Our findings show
that DS can successfully deal with the aforementioned instabilities, opening
the way for further progress.Comment: 11 pages, 15 figures and 2 tables; Added acknowledgment
Improved convergence of Complex Langevin simulations
The sign problem appears in lattice QCD as soon as a non-zero chemical
potential is introduced. This prevents direct simulations to determine the
phase structure of the strongly interacting matter. Complex Langevin methods
have been successfully used for various models or approximations of QCD.
However, in some scenarios it converges to incorrect results. We present
developments of our new method that helps to improve the convergence by keeping
the system closer to the SU(3) manifold and discuss preliminary tests and
results.Comment: 7 pages, 6 figures, talk presented at the 35th International
Symposium on Lattice Field Theory (Lattice 2017), Granada, Spai
Taylor expansion and the Cauchy Residue Theorem for finite-density QCD
We present an update on our efforts to determine the Taylor coefficients of
the expansion of the pressure for finite-density QCD. Here, we explore
alternatives based on the Cauchy Residue Theorem, which allows us to use a
discretized contour to determine the desired spectral moments occurring in the
Taylor expansion of QCD at zero chemical potential.Comment: 6 pages, 4 figures, talk presented at the 36th Annual International
Symposium on Lattice Field Theory, July 22-28, 2018, East Lansing, MI, US
Lattice calculations of the leading hadronic contribution to (g-2)_mu
We report on our ongoing project to calculate the leading hadronic
contribution to the anomalous magnetic moment of the muon a_mu^HLO using two
dynamical flavours of non-perturbatively O(a) improved Wilson fermions. In this
study, we changed the vacuum polarisation tensor to a combination of local and
point-split currents which significantly reduces the numerical effort.
Partially twisted boundary conditions allow us to improve the momentum
resolution of the vacuum polarisation tensor and therefore the determination of
the leading hadronic contribution to (g-2)_mu. We also extended the range of
ensembles to include a pion mass below 200 MeV which allows us to check the
non-trivial chiral behaviour of a_mu^HLO.Comment: 7 pages, 3 figures, 1 table, talk presented at the 30th International
Symposium on Lattice Field Theory (Lattice2012), Cairns, Australi
Improved interpolating fields for hadrons at non-vanishing momentum
We demonstrate that a reduction in the noise-to-signal ratio may be obtained
for hadrons at non-zero momenta whilst maintaining a good overlap with the
ground state through a generalisation of Gaussian/Wuppertal smearing. The use
of an anisotropic smearing wavefunction is motivated by the physical picture of
a boosted hadron.Comment: 7 pages, 6 figures, poster presented at the 30th International
Symposium on Lattice Field Theory (Lattice 2012), Cairns, Australia, June
24-29, 201
The Shape of Covariantly Smeared Sources in Lattice QCD
Covariantly smeared sources are commonly used in lattice QCD to enhance the
projection onto the ground state. Here we investigate the dependence of their
shape on the gauge field background and find that the presence of localized
concentrations of magnetic field can lead to strong distortions which reduce
the smearing radii achievable by iterative smearing prescriptions. In
particular, as , iterative procedures like Jacobi smearing require
increasingly large iteration counts in order to reach physically-sized smearing
radii 0.5 fm, and the resulting sources are strongly distorted. To
bypass this issue, we propose a covariant smearing procedure (``free-form
smearing'') that allows us to create arbitrarily shaped sources, including in
particular Gaussians of arbitrary radius.Comment: 1+15 pages, 7 figures (24 pdf images
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