1,545 research outputs found
Topological Susceptibility from Slabs
In quantum field theories with topological sectors, a non-perturbative
quantity of interest is the topological susceptibility chi_t. In principle it
seems straightforward to measure chi_t by means of Monte Carlo simulations.
However, for local update algorithms and fine lattice spacings, this tends to
be difficult, since the Monte Carlo history rarely changes the topological
sector. Here we test a method to measure chi_t even if data from only one
sector are available. It is based on the topological charges in sub-volumes,
which we denote as slabs. Assuming a Gaussian distribution of these charges,
this method enables the evaluation of chi_t, as we demonstrate with numerical
results for non-linear sigma-models.Comment: 23 pages, 8 figures, 6 table
Innovationsmotor für zukünftige Landwirtschaft
Prinzip des Ökolandbaus ist, Nahrung zu sichern und dabei die Belastbarkeit von Ökosystemen zu berücksichtigen. Die Forschung zum Ökolandbau leistet dazu unverzichtbare Beiträge.
Was kann sie konkret für die Entwicklung von Innovationen in der nachhaltigen Landwirtschaft und zur Sicherung der Ernährung beitragen
SU(3) Quantum Spin Ladders as a Regularization of the CP(2) Model at Non-Zero Density: From Classical to Quantum Simulation
Quantum simulations would be highly desirable in order to investigate the
finite density physics of QCD. -d quantum field
theories are toy models that share many important features of QCD: they are
asymptotically free, have a non-perturbatively generated massgap, as well as
-vacua. quantum spin ladders provide an unconventional
regularization of models that is well-suited for quantum
simulation with ultracold alkaline-earth atoms in an optical lattice. In order
to validate future quantum simulation experiments of models at
finite density, here we use quantum Monte Carlo simulations on classical
computers to investigate quantum spin ladders at non-zero chemical
potential. This reveals a rich phase structure, with single- or double-species
Bose-Einstein "condensates", with or without ferromagnetic order
The Slab Method to Measure the Topological Susceptibility
In simulations of a model with topological sectors, algorithms which proceed
in small update steps tend to get stuck in one sector, especially on fine
lattices. This distorts the numerical results; in particular it is not
straightforward to measure the topological susceptibility chi_t. We test a
method to measure chi_t even if configurations from only one sector are
available. It is based on the topological charges in sub-volumes, which we
denote as "slab". This enables the evaluation of chi_t, as we demonstrate with
numerical results for non-linear sigma-models and for 2-flavour QCD. In the
latter case, the gradient flow is applied for the smoothing of the gauge
configurations, and the slab method results for chi_t are stable over a broad
range of flow times.Comment: 7 pages, 7 figures, talk presented at the 34th International
Symposium on Lattice Field Theory, 24-30 July 2016, Southampton, UK. Minor
corrections, references added, Fig. 5 replace
Topology in the 2d Heisenberg Model under Gradient Flow
The 2d Heisenberg model --- or 2d O(3) model --- is popular in condensed
matter physics, and in particle physics as a toy model for QCD. Along with
other analogies, it shares with 4d Yang-Mills theories, and with QCD, the
property that the configurations are divided in topological sectors. In the
lattice regularisation the topological charge can still be defined such
that . It has generally been observed, however, that the
topological susceptibility does not
scale properly in the continuum limit, i.e. that the quantity diverges for (where is the correlation length in
lattice units). Here we address the question whether or not this divergence
persists after the application of the Gradient Flow.Comment: 10 pages, LaTex, 7 figures, 2 tables, talk presented at the XXXI
Reuni\'on Anual de la Divisi\'on de Part\'iculas y Campos de la Sociedad
Mexicana de F\'isica (CINVESTAV, Mexico City
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