8,846 research outputs found
The Effect of LHC Jet Data on MSTW PDFs
We consider the effect on LHC jet cross sections on partons distribution
functions (PDFs), in particular the MSTW2008 set of PDFs. We first compare the
published inclusive jet data to the predictions using MSTW2008, finding a very
good description. We also use the parton distribution reweighting procedure to
estimate the impact of these new data on the PDFs, finding that the combined
ATLAS 2.76 TeV and 7 TeV data, and CMS 7 TeV data have some significant impact.
We then also investigate the impact of ATLAS, CMS and D0 dijet data using the
same techniques. In this case we investigate the effect of using different
scale choices for the NLO cross section calculation. We find that the dijet
data is generally not completely compatible with the corresponding inclusive
jet data, often tending to pull PDFs, particularly the gluon distribution, away
from the default values. However, the effect depends on the dijet data set used
as well as the scale choice. We also note that conclusions may be affected by
limiting the pull on the data luminosity chosen by the best fit, which is
sometimes a number of standard deviations. Finally we include the inclusive jet
data in a new PDF fit explicitly. This enables us to check the consistency of
the exact result with that obtained from the reweighting procedure. There is
generally good, but not full quantitative agreement. Hence, the conclusion
remains that MSTW2008 PDFs already fit the published jet data well, but the
central values and uncertainties are altered and improved respectively by
significant, but not dramatic extent by inclusion of these data.Comment: 63 pages, 50 figures. Final version. Some added discussion and
improved figure
Deconstructing double-barred galaxies in 2D and 3D. II. Two distinct groups of inner bars
The intrinsic photometric properties of inner and outer stellar bars within
17 double-barred galaxies are thoroughly studied through a photometric analysis
consisting of: i) two-dimensional multi-component photometric decompositions,
and ii) three-dimensional statistical deprojections for measuring the
thickening of bars, thus retrieving their 3D shape. The results are compared
with previous measurements obtained with the widely used analysis of integrated
light. Large-scale bars in single- and double-barred systems show similar
sizes, and inner bars may be longer than outer bars in different galaxies. We
find two distinct groups of inner bars attending to their in-plane length and
ellipticity, resulting in a bimodal behaviour for the inner/outer bar length
ratio. Such bimodality is related neither to the properties of the host galaxy
nor the dominant bulge, and it does not show a counterpart in the dimension off
the disc plane. The group of long inner bars lays at the lower end of the outer
bar length vs. ellipticity correlation, whereas the short inner bars are out of
that relation. We suggest that this behaviour could be due to either a
different nature of the inner discs from which the inner bars are dynamically
formed, or a different assembly stage for the inner bars. This last possibility
would imply that the dynamical assembly of inner bars is a slow process taking
several Gyr to happen. We have also explored whether all large-scale bars are
prone to develop an inner bar at some stage of their lives, possibility we
cannot fully confirm or discard.Comment: 14 pages, 8 figures, 1 table. Accepted for publication in MNRA
Evidence-based factual error correction
This paper introduces the task of factual error correction: performing edits to a claim so that the generated rewrite is better supported by evidence. This extends the well-studied task of fact verification by providing a mechanism to correct written texts that are refuted or only partially supported by evidence. We demonstrate that it is feasible to train factual error correction systems from existing fact checking datasets which only contain labeled claims accompanied by evidence, but not the correction. We achieve this by employing a two-stage distant supervision approach that incorporates evidence into masked claims when generating corrections. Our approach, based on the T5 transformer and using retrieved evidence, achieved better results than existing work which used a pointer copy network and gold evidence, producing accurate factual error corrections for 5x more instances in human evaluation and a.125 increase in SARI score. The evaluation is conducted on a dataset of 65,000 instances based on a recent fact verification shared task and we release it to enable further work on the task
Recent Progress in Parton Distributions and Implications for LHC Physics
I outline some of the most recent developments on the global fit to parton
distributions performed by the MRST collaboration.Comment: 6 pages, 7 figures. To appear in proceedings of XIII International
Workshop on Deep Inelastic Scattering, April,27 - May,1, 2005, Madison,
Wisconsin, US
Waveless Approximation Theories of Gravity
The analysis of a general multibody physical system governed by Einstein's
equations in quite difficult, even if numerical methods (on a computer) are
used. Some of the difficulties -- many coupled degrees of freedom, dynamic
instability -- are associated with the presence of gravitational waves. We have
developed a number of ``waveless approximation theories'' (WAT) which repress
the gravitational radiation and thereby simplify the analysis. The matter,
according to these theories, evolves dynamically. The gravitational field,
however, is determined at each time step by a set of elliptic equations with
matter sources. There is reason to believe that for many physical systems, the
WAT-generated system evolution is a very accurate approximation to that
generated by the full Einstein theory
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