1,556 research outputs found
Isolated Photons in Deep Inelastic Scattering
Photon radiation at large transverse momenta at colliders is a detailed probe
of hard interaction dynamics. The isolated photon production cross section in
deep inelastic scattering was measured recently by the ZEUS experiment, and
found to be considerably larger than theoretical predictions obtained with
widely used event generators. To investigate this discrepancy, we perform a
dedicated parton-level calculation of this observable, including contributions
from fragmentation and large-angle radiation. Our results are in good agreement
with all aspects of the experimental measurement.Comment: 4 pages, 3 figure
Two-Loop Quark and Gluon Form Factors in Dimensional Regularisation
We compute the two-loop corrections to the massless quark form factor
and gluon form factor to all orders in the
dimensional regularisation parameter . The two-loop
contributions to the form factors are reduced to linear combinations of master
integrals, which are computed in a closed form, expressed as -functions
and generalised hypergeometric functions of unit argument. Using the newly
developed HypExp-package, these can be expanded to any desired order, yielding
Laurent expansions in . We provide expansions of the form factors to
order , as required for ultraviolet renormalisation and infrared
factorisation of the three-loop form factors.Comment: 9 pages, latex, references update
NNLO QCD corrections to event shape variables in electron positron annihilation
Precision studies of QCD at electron-positron colliders are based on
measurements of event shapes and jet rates. To match the high experimental
accuracy, theoretical predictions to next-to-next-to-leading order (NNLO) in
QCD are needed for a reliable interpretation of the data. We report the first
calculation of NNLO corrections O(alpha_s^3) to three-jet production and
related event shapes, and discuss their phenomenological impact.Comment: Contributed to 2007 Europhysics Conference on High Energy Physics,
Manchester, England 19-25 July 200
Characterisation of red-giant stars in the public Kepler data
The first public release of long-cadence stellar photometric data collected
by the NASA Kepler mission has now been made available. In this paper we
characterise the red-giant (G-K) stars in this large sample in terms of their
solar-like oscillations. We use published methods and well-known scaling
relations in the analysis. Just over 70% of the red giants in the sample show
detectable solar-like oscillations, and from these oscillations we are able to
estimate the fundamental properties of the stars. This asteroseismic analysis
reveals different populations: low-luminosity H-shell burning red-giant branch
stars, cool high-luminosity red giants on the red-giant branch and He-core
burning clump and secondary-clump giants.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society Main Journa
Solar-like oscillations in red giants observed with Kepler: comparison of global oscillation parameters from different methods
The large number of stars for which uninterrupted high-precision photometric
timeseries data are being collected with \textit{Kepler} and CoRoT initiated
the development of automated methods to analyse the stochastically excited
oscillations in main-sequence, subgiant and red-giant stars. Aims: We
investigate the differences in results for global oscillation parameters of G
and K red-giant stars due to different methods and definitions. We also
investigate uncertainties originating from the stochastic nature of the
oscillations. Methods: For this investigation we use Kepler data obtained
during the first four months of operation. These data have been analysed by
different groups using already published methods and the results are compared.
We also performed simulations to investigate the uncertainty on the resulting
parameters due to different realizations of the stochastic signal. Results: We
obtain results for the frequency of maximum oscillation power (nu_max) and the
mean large separation () from different methods for over one thousand
red-giant stars. The results for these parameters agree within a few percent
and seem therefore robust to the different analysis methods and definitions
used here. The uncertainties for nu_max and due to differences in
realization noise are not negligible and should be taken into account when
using these results for stellar modelling.Comment: 11 pages, 9 Figures and 7 tables, accepted for publication in
Astronomy and Astrophysic
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