45,857 research outputs found
All-Order Corrections To Higgs Boson Production In Association With Jets
We present a new framework for calculating multi-jet observables. The
framework is based on the factorisation of scattering amplitudes in the
kinematical limit of large invariant mass between all particles. We show that
by constraining the analyticity of scattering amplitudes away from this limits,
we get good agreement order by order with the full, fixed order perturbative
calculation at the low orders where these are available, and therefore get firm
predictions on the all-order behaviour. As an example, we study Higgs boson
production through gluon fusion in association with at least two jets at the
LHC.Comment: Invited talk at 44th Rencontres de Moriond on QCD and High Energy
Interactions, La Thuile, Valle d'Aosta, Italy, 14-21 Mar 200
A Closer look at the analysis of NLL BFKL.
The initial analyses of the next-to-leading logarithmic corrections to the BFKL kernel were
very discouraging. Encouraged by the success of new methods in the analysis of the BFKL
equation at full NLL accuracy we demonstrate in this talk how some of the initial conclusions
were based on a breakdown of the tools used in the analysis rather than the framework itself
A New approach to inclusive decay spectra.
The main obstacle in describing inclusive decay spectra in QCD â which, in particular, limits
the precision in extrapolating the measured ÂŻB ââ Xs
rate to the full phase space as well as
in extracting |Vub| from inclusive measurements of charmless semileptonic decays â is their
sensitivity to the non-perturbative momentum distribution of the heavy quark in the meson.
We show that, despite this sensitivity, resummed perturbation theory has high predictive
power. Conventional Sudakovâresummed perturbation theory describing the decay of an onshell
heavy quark yields a divergent expansion. Detailed understanding of this divergence
in terms of infrared renormalons has paved the way for making quantitative predictions. In
particular, the leading renormalon ambiguity cancels out between the Sudakov factor and
the quark pole mass. This cancellation requires renormalon resummation but involves no
non-perturbative information. Additional effects due to the Fermi motion of the quark in
the meson can be systematically taken into account through power corrections, which are only
important near the physical endpoint. This way the moments of the ÂŻB ââ Xs
spectrum with
experimentallyâaccessible cuts â which had been so far just parametrized â were recently
computed by perturbative means. At Moriond these predictions were confronted with new
data from BaBar
Plasmon dispersion in semimetallic armchair graphene nanoribbons
The dispersion relations for plasmons in intrinsic and extrinsic semimetallic
armchair graphene nanoribbons (acGNR) are calculated in the random phase
approximation using the orthogonal p_z-orbital tight binding method. Our model
predicts new plasmons for acGNR of odd atomic widths N=5,11,17,... Our model
further predicts plasmons in acGNR of even atomic width N=2,8,14,... related to
those found using a Dirac continuum model, but with different quantitative
dispersion characteristics. We find that the dispersion of all plasmons in
semimetallic acGNR depends strongly on the localization of the p_z electronic
wavefunctions. We also find that overlap integrals for acGNR behave in a more
complex way than predicted by the Dirac continuum model, suggesting that these
plasmons will experience a small damping for all q not equal to 0. Plasmons in
extrinsic semimetallic acGNR with the chemical potential in the lowest
(highest) conduction (valence) band are found to have dispersion
characteristics nearly identical to their intrinsic counterparts, with
negligible differencs in dispersion arising from the slight differences in
overlap integrals for the interband and intraband transitions.Comment: 8 pages, 9 figure
Coding of the Reach Vector in Parietal Area 5d
Competing models of sensorimotor computation predict different topological constraints in the brain. Some models propose population coding of particular reference frames in anatomically distinct nodes, whereas others require no such dedicated subpopulations and instead predict that regions will simultaneously code in multiple, intermediate, reference frames. Current empirical evidence is conflicting, partly due to difficulties involved in identifying underlying reference frames. Here, we independently varied the locations of hand, gaze, and target over many positions while recording from the dorsal aspect of parietal area 5. We find that the target is represented in a predominantly hand-centered reference frame here, contrasting with the relative code seen in dorsal premotor cortex and the mostly gaze-centered reference frame in the parietal reach region. This supports the hypothesis that different nodes of the sensorimotor circuit contain distinct and systematic representations, and this constrains the types of computational model that are neurobiologically relevant
All-Order Corrections and Multi-Jet Rates
We discuss results from a recently proposed all-order description of hard,
radiative corrections to certain multi-jet processes at hadron colliders. The
description is based on obtaining an all-order estimate of the t-channel
singularities of scattering amplitudes. As a simple example, we illustrate the
similarities between qQ and qg-scattering. In particular, we discuss how at
tree-level, all non-suppressed helicity-amplitudes for these processes consist
of a pure t-channel pole. This structure is used in the construction of
all-order approximations.Comment: 6 pages. Talk given at RADCOR 2009 - 9th International Symposium on
Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology), October 25 - 30 2009, Ascona, Switzerlan
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