45,367 research outputs found
Strong tW Scattering at the LHC
Deviations of the top electroweak couplings from their Standard Model values
imply that certain amplitudes for the scattering of third generation fermions
and longitudinally polarized vector bosons or Higgses diverge quadratically
with momenta. This high-energy growth is a genuine signal of models where the
top quark is strongly coupled to the sector responsible for electroweak
symmetry breaking. We propose to profit from the high energies accessible at
the LHC to enhance the sensitivity to non-standard top- couplings, which are
currently very weakly constrained. To demonstrate the effectiveness of the
approach, we perform a detailed analysis of scattering, which can
be probed at the LHC via . By recasting a CMS analysis at 8
TeV, we derive the strongest direct bounds to date on the couplings. We
also design a dedicated search at 13 TeV that exploits the distinctive features
of the signal. Finally, we present other scattering processes in
the same class that could provide further tests of the top-Higgs sector.Comment: 37 pages, 10 figures; v2: minor improvements in the discussion,
references added. Matches version published in JHE
On The Complexity and Completeness of Static Constraints for Breaking Row and Column Symmetry
We consider a common type of symmetry where we have a matrix of decision
variables with interchangeable rows and columns. A simple and efficient method
to deal with such row and column symmetry is to post symmetry breaking
constraints like DOUBLELEX and SNAKELEX. We provide a number of positive and
negative results on posting such symmetry breaking constraints. On the positive
side, we prove that we can compute in polynomial time a unique representative
of an equivalence class in a matrix model with row and column symmetry if the
number of rows (or of columns) is bounded and in a number of other special
cases. On the negative side, we show that whilst DOUBLELEX and SNAKELEX are
often effective in practice, they can leave a large number of symmetric
solutions in the worst case. In addition, we prove that propagating DOUBLELEX
completely is NP-hard. Finally we consider how to break row, column and value
symmetry, correcting a result in the literature about the safeness of combining
different symmetry breaking constraints. We end with the first experimental
study on how much symmetry is left by DOUBLELEX and SNAKELEX on some benchmark
problems.Comment: To appear in the Proceedings of the 16th International Conference on
Principles and Practice of Constraint Programming (CP 2010
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