4,274 research outputs found
High multiplicity processes at NLO with BlackHat and Sherpa
In this contribution we review recent progress with fixed-order QCD
predictions for the production of a vector boson in association with jets at
hadron colliders, using the programs BlackHat and SHERPA. We review general
features of next-to-leading-order (NLO) predictions for the production of a
massive vector boson in association with four jets. We also discuss how precise
descriptions of vector-boson production can be applied to the determination of
backgrounds to new physics signals. Here we focus on data-driven backgrounds to
a missing-energy-plus-jets search performed by CMS. Finally, we review recent
progress in developing theoretical tools for high-multiplicity loop-computation
within the BlackHat-library. In particular, we discuss methods for handling the
color degrees of freedom in multi-jet predictions at NLO.Comment: 12 pages, contribution to the proceedings of Loops and Legs 201
Parallelization of irregularly coupled regular meshes
Regular meshes are frequently used for modeling physical phenomena on both serial and parallel computers. One advantage of regular meshes is that efficient discretization schemes can be implemented in a straight forward manner. However, geometrically-complex objects, such as aircraft, cannot be easily described using a single regular mesh. Multiple interacting regular meshes are frequently used to describe complex geometries. Each mesh models a subregion of the physical domain. The meshes, or subdomains, can be processed in parallel, with periodic updates carried out to move information between the coupled meshes. In many cases, there are a relatively small number (one to a few dozen) subdomains, so that each subdomain may also be partitioned among several processors. We outline a composite run-time/compile-time approach for supporting these problems efficiently on distributed-memory machines. These methods are described in the context of a multiblock fluid dynamics problem developed at LaRC
Modeling and optimum time performance for concurrent processing
The development of a new graph theoretic model for describing the relation between a decomposed algorithm and its execution in a data flow environment is presented. Called ATAMM, the model consists of a set of Petri net marked graphs useful for representing decision-free algorithms having large-grained, computationally complex primitive operations. Performance time measures which determine computing speed and throughput capacity are defined, and the ATAMM model is used to develop lower bounds for these times. A concurrent processing operating strategy for achieving optimum time performance is presented and illustrated by example
Decomposition algebras and axial algebras
We introduce decomposition algebras as a natural generalization of axial
algebras, Majorana algebras and the Griess algebra. They remedy three
limitations of axial algebras: (1) They separate fusion laws from specific
values in a field, thereby allowing repetition of eigenvalues; (2) They allow
for decompositions that do not arise from multiplication by idempotents; (3)
They admit a natural notion of homomorphisms, making them into a nice category.
We exploit these facts to strengthen the connection between axial algebras and
groups. In particular, we provide a definition of a universal Miyamoto group
which makes this connection functorial under some mild assumptions. We
illustrate our theory by explaining how representation theory and association
schemes can help to build a decomposition algebra for a given (permutation)
group. This construction leads to a large number of examples. We also take the
opportunity to fix some terminology in this rapidly expanding subject.Comment: 23 page
A computer algebra user interface manifesto
Many computer algebra systems have more than 1000 built-in functions, making
expertise difficult. Using mock dialog boxes, this article describes a proposed
interactive general-purpose wizard for organizing optional transformations and
allowing easy fine grain control over the form of the result even by amateurs.
This wizard integrates ideas including:
* flexible subexpression selection;
* complete control over the ordering of variables and commutative operands,
with well-chosen defaults;
* interleaving the choice of successively less main variables with applicable
function choices to provide detailed control without incurring a combinatorial
number of applicable alternatives at any one level;
* quick applicability tests to reduce the listing of inapplicable
transformations;
* using an organizing principle to order the alternatives in a helpful
manner;
* labeling quickly-computed alternatives in dialog boxes with a preview of
their results,
* using ellipsis elisions if necessary or helpful;
* allowing the user to retreat from a sequence of choices to explore other
branches of the tree of alternatives or to return quickly to branches already
visited;
* allowing the user to accumulate more than one of the alternative forms;
* integrating direct manipulation into the wizard; and
* supporting not only the usual input-result pair mode, but also the useful
alternative derivational and in situ replacement modes in a unified window.Comment: 38 pages, 12 figures, to be published in Communications in Computer
Algebr
Cycle decompositions: from graphs to continua
We generalise a fundamental graph-theoretical fact, stating that every
element of the cycle space of a graph is a sum of edge-disjoint cycles, to
arbitrary continua. To achieve this we replace graph cycles by topological
circles, and replace the cycle space of a graph by a new homology group for
continua which is a quotient of the first singular homology group . This
homology seems to be particularly apt for studying spaces with infinitely
generated , e.g. infinite graphs or fractals.Comment: Advances in Mathematics (2011
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