15,712 research outputs found
Aspects of power corrections in hadron-hadron collisions
The program of understanding inverse-power law corrections to event shapes
and energy flow observables in e+ e- annihilation to two jets and DIS (1+1)
jets has been a significant success of QCD phenomenology over the last decade.
The important extension of this program to similar observables in hadron
collisions is not straightforward, being obscured by both conceptual and
technical issues. In this paper we shed light on some of these issues by
providing an estimate of power corrections to the inter-jet E_t flow
distribution in hadron collisions using the techniques that were employed in
the e+ e- annihilation and DIS cases.Comment: 15 pages, 1 figure, uses JHEP3.cl
Angular ordering and parton showers for non-global QCD observables
We study the mismatch between a full calculation of non-global
single-logarithms in the large-N_c limit and an approximation based on free
azimuthal averaging, and the consequent angular-ordered pattern of soft gluon
radiation in QCD. We compare the results obtained in either case to those
obtained from the parton showers in the Monte Carlo event generators HERWIG and
PYTHIA, with the aim of assessing the accuracy of the parton showers with
regard to such observables where angular ordering is merely an approximation
even at leading-logarithmic accuracy and which are commonly employed for the
tuning of event generators to data.Comment: 20 pages, 8 figure
The aT distribution of the Z boson at hadron colliders
We provide the first theoretical study of a novel variable, , proposed
in Ref.[1] as a more accurate probe of the region of low transverse momentum
, for the boson distribution at hadron colliders. The is
the component of transverse to a suitably defined axis. Our study
involves resummation of large logarithms in up to the next-to--leading
logarithmic accuracy and we compare the results to those for the well-known
distribution, identifying important physical differences between the two
cases. We also test our resummed result at the two-loop level by comparing its
expansion to order with the corresponding fixed-order results and
find agreement with our expectations.Comment: 30 pages, 3 figures, JHEP class included. Final version published in
JHE
Problems in resumming interjet energy flows with k_t clustering
We consider the energy flow into gaps between hard jets. It was previously
believed that the accuracy of resummed predictions for such observables can be
improved by employing the clustering procedure to define the gap energy
in terms of a sum of energies of soft jets (rather than individual hadrons) in
the gap. This significantly reduces the sensitivity to correlated soft
large-angle radiation (non-global leading logs), numerically calculable only in
the large limit. While this is the case, as we demonstrate here, the use
of clustering spoils the straightforward single-gluon Sudakov
exponentiation that multiplies the non-global resummation. We carry out an
calculation of the leading single-logarithmic terms
and identify the piece that is omitted by straightforward exponentiation. We
compare our results with the full result from the
program EVENT2 to confirm our conclusions. For jets and DIS
(1+1) jets one can numerically resum these additional contributions as we show,
but for dijet photoproduction and hadron-hadron processes further studies are
needed.Comment: 11 pages, 5 figure
Banded spatiotemporal chaos in sheared nematogenic fluids
We present the results of a numerical study of a model of the hydrodynamics
of a sheared nematogenic fluid, taking into account the effects of order
parameter stresses on the velocity profile, but allowing spatial variations
only in the gradient direction. When parameter values are such that the stress
from orientational distortions is comparable to the bare viscous stress, the
system exhibits steady states with the characteristics of shear banding. In
addition, nonlinearity in the coupling of extensional flow to orientation leads
to the appearance of a new steady state in which the features of both
spatiotemporal chaos and shear banding are present.Comment: 4 pages, 6 figures.(Some of the figures have low resolution so as to
fit the requirements of arxiv.
The Hessian biased singular value decomposition method for optimization and analysis of force fields
We present methodology (HBFF/SVD) for optimizing the form and parameters of force fields (FF) for molecular dynamics simulations through utilizing information about properties such as the geometry, Hessian, polarizability, stress (crystals), and elastic constants (crystals). This method is based on singular value decomposition (SVD) of the Jacobian describing the partial derivatives in various properties with respect to FF parameters. HBFF/SVD is effective for optimizing the parameters for accurate FFs of organic, inorganic, and transition metal compounds. In addition it provides information on the validity of the functional form of the FF for describing the properties of interest. This method is illustrated by application to organic molecules (CH2O, C2H4, C4H6, C6H8, C6H6, and naphthalene) and inorganic molecules (Cl2CrO2 and Cl2MoO2)
Dual purpose optical instrument capable of simultaneously acting as spectrometer and diffractometer
A dual purpose optical instrument is described capable of simultaneously acting as a spectrometer and diffractometer to respectively perform elemental and structural analysis of an unknown sample. The diffractometer portion of the instrument employs a modified form of Seeman-Bohlin focusing which involves providing a line source of X-rays, a sample, and a detector, all on the same focal circle. The spectrometer portion of the instrument employs a fixedly mounted X-ray energy detector mounted outside of the plane of the focal circle
A Lorentzian cure for Euclidean troubles
There is strong evidence coming from Lorentzian dynamical triangulations that
the unboundedness of the gravitational action is no obstacle to the
construction of a well-defined non-perturbative path integral. In a continuum
approach, a similar suppression of the conformal divergence comes about as the
result of a non-trivial path-integral measure.Comment: 3 page
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