4,554 research outputs found
Color screening in flavor QCD at large distances
We study correlation functions of spatially separated static quark-antiquark
pairs in flavor QCD in order to investigate the nature of color screening
at high temperatures. We perform lattice calculations in a wide temperature
range, , using the highly improved
staggered quark (HISQ) action and several lattice spacings to control
discretization effects. We alleviate the UV noise problem through the use of
four dimensional hypercubic (HYP) smearing, which enables the reconstruction of
correlators and determination of screening properties even at low temperatures
and at large distances.Comment: 8 pages, 9 figure
Knowledge Does Not Fall Far from the Tree - A Case Study on the Diffusion of Solar Cells in Germany
The purpose of this paper is to illuminate the geographical diffusion of photovoltaic installations in Germany quantitatively and to test if preexisting photovoltaic systems stimulate further installations nearby; thus we investigate to which extent knowledge flows depend on geographic proximity. We develop an econometric model, which is discrete in time and space, but the level of geographical agglomeration is adjustable in arbitrarily small steps. We find that the probability to install a photovoltaic system dependents on the geographic proximity to agents, who have previously installed a photovoltaic system. In conclusion, our results confirm that knowledge exchange attenuates with distance.
Minimally doubled fermions at one loop
Minimally doubled fermions have been proposed as a cost-effective realization
of chiral symmetry at non-zero lattice spacing. Using lattice perturbation
theory at one loop, we study their renormalization properties. Specifically, we
investigate the consequences of the breaking of hyper-cubic symmetry, which is
a typical feature of this class of fermionic discretizations. Our results for
the quark self-energy indicate that the four-momentum undergoes a
renormalization which contains a linearly divergent piece. We also compute
renormalization factors for quark bilinears, construct the conserved vector and
axial-vector currents and verify that at one loop the renormalization factors
of the latter are equal to one.Comment: 11 pages, 1 figure, discussion of renormalization of four-momentum
modified, increased numerical precision of one-loop integrals, results and
conclusions unchange
Speeding up SOR Solvers for Constraint-based GUIs with a Warm-Start Strategy
Many computer programs have graphical user interfaces (GUIs), which need good
layout to make efficient use of the available screen real estate. Most GUIs do
not have a fixed layout, but are resizable and able to adapt themselves.
Constraints are a powerful tool for specifying adaptable GUI layouts: they are
used to specify a layout in a general form, and a constraint solver is used to
find a satisfying concrete layout, e.g.\ for a specific GUI size. The
constraint solver has to calculate a new layout every time a GUI is resized or
changed, so it needs to be efficient to ensure a good user experience. One
approach for constraint solvers is based on the Gauss-Seidel algorithm and
successive over-relaxation (SOR).
Our observation is that a solution after resizing or changing is similar in
structure to a previous solution. Thus, our hypothesis is that we can increase
the computational performance of an SOR-based constraint solver if we reuse the
solution of a previous layout to warm-start the solving of a new layout. In
this paper we report on experiments to test this hypothesis experimentally for
three common use cases: big-step resizing, small-step resizing and constraint
change. In our experiments, we measured the solving time for randomly generated
GUI layout specifications of various sizes. For all three cases we found that
the performance is improved if an existing solution is used as a starting
solution for a new layout
Spin-taste structure of minimally doubled fermions
Minimally doubled fermions realize one degenerate pair of Dirac fermions on
the lattice. Similarities to staggered fermions exist, namely, spin and taste
degrees of freedom become intertwined, and a remnant, non-singlet chiral
symmetry and ultralocality are maintained. However, charge conjugation,
isotropy and some space-time reflection symmetries are broken by the cutoff.
For two variants, i.e., Karsten-Wilczek (KW) or Borici-Creutz (BC) fermions, a
tasted charge conjugation symmetry can be identified, and the respective
representations of the spin-taste algebra can be constructed explicitly. In the
case of BC fermions, the tasted symmetry indicates that amendments to the
published counterterms are necessary. The spin-taste representation on the
quark level permits construction of local or extended hadron interpolating
operators for any spin-taste combination, albeit with contamination by parity
partners and taste-symmetry violation. The few available numerical results for
KW fermions are in line with expectations.Comment: 9 pages, 0 figures; Parallel talk at The 40th International Symposium
on Lattice Field Theory (Lattice 2023), July 31st - August 4th, 2023, Fermi
National Accelerator Laborator
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