4,938 research outputs found
Critical temperature of Heisenberg models on regular trees, via random loops
We estimate the critical temperature of a family of quantum spin systems on
regular trees of large degree. The systems include the spin- XXZ model
and the spin-1 nematic model. Our formula is conjectured to be valid for
large-dimensional cubic lattices. Our method of proof uses a probabilistic
representation in terms of random loops.Comment: 14 pages, to appear in J. Stat. Phy
A Generic Framework for Engineering Graph Canonization Algorithms
The state-of-the-art tools for practical graph canonization are all based on
the individualization-refinement paradigm, and their difference is primarily in
the choice of heuristics they include and in the actual tool implementation. It
is thus not possible to make a direct comparison of how individual algorithmic
ideas affect the performance on different graph classes.
We present an algorithmic software framework that facilitates implementation
of heuristics as independent extensions to a common core algorithm. It
therefore becomes easy to perform a detailed comparison of the performance and
behaviour of different algorithmic ideas. Implementations are provided of a
range of algorithms for tree traversal, target cell selection, and node
invariant, including choices from the literature and new variations. The
framework readily supports extraction and visualization of detailed data from
separate algorithm executions for subsequent analysis and development of new
heuristics.
Using collections of different graph classes we investigate the effect of
varying the selections of heuristics, often revealing exactly which individual
algorithmic choice is responsible for particularly good or bad performance. On
several benchmark collections, including a newly proposed class of difficult
instances, we additionally find that our implementation performs better than
the current state-of-the-art tools
Data-Driven Precision Luminosity Measurements with Z Bosons at the LHC and HL-LHC
A method to measure integrated luminosities at the LHC using Z bosons without
theoretical cross section input is discussed. The main uncertainties and the
prospects for precision luminosity measurements using this method are outlined.Comment: Minor revisio
CLS 2+1 flavor simulations at physical light- and strange-quark masses
We report recent efforts by CLS to generate an ensemble with physical light-
and strange-quark masses in a lattice volume of 192x96^3 at
corresponding to a lattice spacing of 0.064 fm. This ensemble is being
generated as part of the CLS 2+1 flavor effort with improved Wilson fermions.
Our simulations currently cover 5 lattice spacings ranging from 0.039 fm to
0.086 fm at various pion masses along chiral trajectories with either the sum
of the quark masses kept fixed, or with the strange-quark mass at the physical
value. The current status of simulations is briefly reviewed, including a short
discussion of measured autocorrelation times and of the main features of the
simulations. We then proceed to discuss the thermalization strategy employed
for the generation of the physical quark-mass ensemble and present first
results for some simple observables. Challenges encountered in the simulation
are highlighted.Comment: 7 pages, 8 figures; Proceedings, 35th International Symposium on
Lattice Field Theory (Lattice2017): Granada, Spai
Interference fragmentation functions in electron-positron annihilation
We study the process of electron-positron annihilation into back-to-back
jets, where in each jet a pair of hadrons is detected. The orientation of these
two pairs with respect to each other can be used to extract the interference
fragmentation functions in a clean way, for instance from BELLE or BABAR
experiment data. This is of relevance for studies of the transversity
distribution function.
In particular, we focus on two azimuthal asymmetries. The first one has
already been studied by Artru and Collins, but is now expressed in terms of
interference fragmentation functions. The second asymmetry is new and involves
a function that is related to longitudinal jet handedness. This asymmetry
offers a different way of studying handedness correlations.Comment: 13 pages, 2 figures in .eps forma
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