8,409 research outputs found
Optimized Neural Networks to Search for Higgs Boson Production at the Tevatron
An optimal choice of proper kinematical variables is one of the main steps in
using neural networks (NN) in high energy physics. Our method of the variable
selection is based on the analysis of a structure of Feynman diagrams
(singularities and spin correlations) contributing to the signal and background
processes. An application of this method to the Higgs boson search at the
Tevatron leads to an improvement in the NN efficiency by a factor of 1.5-2 in
comparison to previous NN studies.Comment: 4 pages, 4 figures, partially presented in proceedings of ACAT'02
conferenc
Minimal Gauge Invariant Classes of Tree Diagrams in Gauge Theories
We describe the explicit construction of groves, the smallest gauge invariant
classes of tree Feynman diagrams in gauge theories. The construction is valid
for gauge theories with any number of group factors which may be mixed. It
requires no summation over a complete gauge group multiplet of external matter
fields. The method is therefore suitable for defining gauge invariant classes
of Feynman diagrams for processes with many observed final state particles in
the standard model and its extensions.Comment: 13 pages, RevTeX (EPS figures
Measuring the Higgs Branching Fraction into two Photons at Future Linear \ee Colliders
We examine the prospects for measuring the \gaga branching fraction of a
Standard Model-like Higgs boson with a mass of 120 GeV at the future TESLA
linear \ee collider, assuming an integrated luminosity of 1 ab and
center-of-mass energies of 350 GeV and 500 GeV. The Higgs boson is produced in
association with a fermion pair via the Higgsstrahlung process \ee ,
with \qq or \nn, or the WW fusion reaction . A relative uncertainty on BF(\hgg) of~16% can be achieved in
unpolarized \ee collisions at =~500 GeV, while for =~350
GeV the expected precision is slightly poorer. With appropriate initial state
polarizations BF(\hgg)/BF(\hgg) can be improved to 10%. If this
measurement is combined with the expected error for the total Higgs width, a
precision of 10% on the \gaga Higgs boson partial width appears feasible.Comment: 14 pages, 5 figure
Asymptotically nonlocal gravity
Asymptotically nonlocal field theories interpolate between Lee-Wick theories
with multiple propagator poles, and ghost-free nonlocal theories. Previous work
on asymptotically nonlocal scalar, Abelian, and non-Abelian gauge theories has
demonstrated the existence of an emergent regulator scale that is
hierarchically smaller than the lightest Lee-Wick partner, in a limit where the
Lee-Wick spectrum becomes dense and decoupled. We generalize this construction
to linearized gravity, and demonstrate the emergent regulator scale in three
examples: by studying the resolution of the singularity (i) at the origin in
the classical solution for the metric of a point particle, and (ii) in the
nonrelativistic gravitational potential computed via a one-graviton exchange
amplitude; (iii) we also show how this derived scale regulates the one-loop
graviton contribution to the self energy of a real scalar field. We comment
briefly on the generalization of our approach to the full, nonlinear theory of
gravity.Comment: 18 pages LaTeX, 1 Figure. v2: references added. v3: Discussion
clarified and references adde
Effective Lagrangians for physical degrees of freedom in the Randall-Sundrum model
We derive the second variation Lagrangian of the Randall-Sundrum model with
two branes, study its gauge invariance and diagonalize it in the unitary gauge.
We also show that the effective four-dimensional theory looks different on
different branes and calculate the observable mass spectra and the couplings of
the physical degrees of freedom of 5-dimensional gravity to matter.Comment: 22 pages, LaTeX, typos correcte
Low density of top predators (seabirds and marine mammals) in the high Arctic pack ice
The at-sea distribution of top predators, seabirds and marine mammals, was determined in the high Arctic pack ice on board the icebreaker RV Polarstern in July to September 2014. In total, 1,620 transect counts were realised, lasting 30 min each. The five most numerous seabird species represented 74% of the total of 15,150 individuals registered: kittiwake Rissa tridactyla, fulmar Fulmarus glacialis, puffin Fratercula arctica, Ross’s gull Rhodostethia rosea, and little auk Alle alle. Eight cetacean species were tallied for a total of 330 individuals, mainly white-beaked dolphin Lagenorhynchus albirostris and fin whale Balaenoptera physalus. Five pinniped species were represented by a total of 55 individuals and the polar bear Ursus maritimus was represented by 12 individuals. Four main geographical zones were identified: from Tromsø to the outer marginal ice zone (OMIZ), the Arctic pack ice (close pack ice, CPI), the end of Lomonosov Ridge off Siberia, and the route off Siberia and northern Norway. Important differences were detected between zones, both in species composition and in individual abundance. Low numbers of species and high proportion of individuals for some of them can be considered to reflect very low biodiversity. Numbers encountered in zones 2 to 4 were very low in comparison with other European Arctic seas. The observed differences showed strong patterns
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