354 research outputs found
Pion and Kaon Production in and Collisions at Next-to-Leading Order
We present new sets of fragmentation functions for charged pions and kaons,
both at leading and next-to-leading order. They are fitted to data on inclusive
charged-hadron production in annihilation taken by TPC at PEP (~GeV) and to similar data by ALEPH at LEP, who discriminated between
events with charm, bottom, and light- flavour fragmentation in their
charged-hadron sample. We treat all partons independently and to properly
incorporate the charm and bottom thresholds. Due to the sizeable energy gap
between PEP and LEP, we are sensitive to the scaling violation in the
fragmentation process, which allows us to extract a value for the asymptotic
scale parameter of QCD, . Recent data on inclusive charged-hadron
production in tagged three-jet events by OPAL and similar data for longitudinal
electron polarization by ALEPH allow us to pin down the gluon fragmentation
functions. Our new fragmentation functions lead to an excellent description of
a multitude of other data on inclusive charged-hadron production,
ranging from ~GeV to LEP energy. In addition, they agree nicely
with the transverse-momentum spectra of single charged hadrons measured by H1
and ZEUS in photoproduction at the collider HERA, which represents a
nontrivial check of the factorization theorem of the QCD-improved parton model.Comment: 22 pages, latex, 13 compressed ps figures in separate fil
Influence of heavy modes on perturbations in multiple field inflation
We investigate linear cosmological perturbations in multiple field
inflationary models where some of the directions are light while others are
heavy (with respect to the Hubble parameter). By integrating out the massive
degrees of freedom, we determine the multi-dimensional effective theory for the
light degrees of freedom and give explicitly the propagation matrix that
replaces the effective sound speed of the one-dimensional case. We then examine
in detail the consequences of a sudden turn along the inflationary trajectory,
in particular the possible breakdown of the low energy effective theory in case
the heavy modes are excited. Resorting to a new basis in field space, instead
of the usual adiabatic/entropic basis, we study the evolution of the
perturbations during the turn. In particular, we compute the power spectrum and
compare with the result obtained from the low energy effective theory.Comment: 24 pages, 13 figures; v2 substantial changes in sec.V; v3 matching
the published version on JCA
On primordial trispectrum from exchanging scalar modes in general multiple field inflationary models
We make an complementary investigation of the primordial trispectrum from
exchanging intermediate scalar modes in multi-field inflation models with
generalized kinetic terms. Together with the calculation of irreducible
contributions to the primordial trispectrum in Ref.[103], we give the full
leading-order primordial trispectrum in generalized multi-field models.Comment: 15 pages, 1 figure; v2 references adde
Reassessing changes in diurnal temperature range: Intercomparison and evaluation of existing global data set estimates
Changes in diurnal temperature range (DTR) over global land areas are compared from a broad range of independent data sets. All data sets agree that global-mean DTR has decreased significantly since 1950, with most of that decrease occurring over 1960–1980. The since-1979 trends are not significant, with inter-data set disagreement even over the sign of global changes. Inter-data set spread becomes greater regionally and in particular at the grid box level. Despite this, there is general agreement that DTR decreased in North America, Europe, and Australia since 1951, with this decrease being partially reversed over Australia and Europe since the early 1980s. There is substantive disagreement between data sets prior to the middle of the twentieth century, particularly over Europe, which precludes making any meaningful conclusions about DTR changes prior to 1950, either globally or regionally. Several variants that undertake a broad range of approaches to postprocessing steps of gridding and interpolation were analyzed for two of the data sets. These choices have a substantial influence in data sparse regions or periods. The potential of further insights is therefore inextricably linked with the efficacy of data rescue and digitization for maximum and minimum temperature series prior to 1950 everywhere and in data sparse regions throughout the period of record. Over North America, station selection and homogeneity assessment is the primary determinant. Over Europe, where the basic station data are similar, the postprocessing choices are dominant. We assess that globally averaged DTR has decreased since the middle twentieth century but that this decrease has not been linear
Large slow-roll corrections to the bispectrum of noncanonical inflation
Nongaussian statistics are a powerful discriminant between inflationary
models, particularly those with noncanonical kinetic terms. Focusing on
theories where the Lagrangian is an arbitrary Lorentz-invariant function of a
scalar field and its first derivatives, we review and extend the calculation of
the observable three-point function. We compute the "next-order" slow-roll
corrections to the bispectrum in closed form, and obtain quantitative estimates
of their magnitude in DBI and power-law k-inflation. In the DBI case our
results enable us to estimate corrections from the shape of the potential and
the warp factor: these can be of order several tens of percent. We track the
possible sources of large logarithms which can spoil ordinary perturbation
theory, and use them to obtain a general formula for the scale dependence of
the bispectrum. Our result satisfies the next-order version of Maldacena's
consistency condition and an equivalent consistency condition for the scale
dependence. We identify a new bispectrum shape available at next-order, which
is similar to a shape encountered in Galileon models. If fNL is sufficiently
large this shape may be independently detectable.Comment: v1: 37 pages, plus tables, figures and appendices. v2: supersedes
version published in JCAP; some clarifications and more detailed comparison
with earlier literature. All results unchanged. v3:improvements to some
plots; text unchange
Observation of exclusive DVCS in polarized electron beam asymmetry measurements
We report the first results of the beam spin asymmetry measured in the
reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry
with a sin(phi) modulation is observed, as predicted for the interference term
of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The
amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and
leading-twist pQCD, the alpha is directly proportional to the imaginary part of
the DVCS amplitude.Comment: 6 pages, 5 figure
A Kinematically Complete Measurement of the Proton Structure Function F2 in the Resonance Region and Evaluation of Its Moments
We measured the inclusive electron-proton cross section in the nucleon
resonance region (W < 2.5 GeV) at momentum transfers Q**2 below 4.5 (GeV/c)**2
with the CLAS detector. The large acceptance of CLAS allowed for the first time
the measurement of the cross section in a large, contiguous two-dimensional
range of Q**2 and x, making it possible to perform an integration of the data
at fixed Q**2 over the whole significant x-interval. From these data we
extracted the structure function F2 and, by including other world data, we
studied the Q**2 evolution of its moments, Mn(Q**2), in order to estimate
higher twist contributions. The small statistical and systematic uncertainties
of the CLAS data allow a precise extraction of the higher twists and demand
significant improvements in theoretical predictions for a meaningful comparison
with new experimental results.Comment: revtex4 18 pp., 12 figure
Next-to-Leading Order Fragmentation Functions for Pions and Kaons
We present new sets of fragmentation functions for charged pions and kaons,
both at leading and next-to-leading order. They are fitted to TPC data taken at
energy ~GeV and describe excellently a wealth of other
data on charged-hadron production, ranging from ~GeV way up to
LEP~1 energy. They also agree with data on the production of neutral pions and
kaons, if one makes the natural assumption that the respective fragmentation
functions are related to the charged counterparts by SU(2) symmetry. We also
list simple parameterizations of the and dependence of our results,
which may be implemented conveniently in applications.Comment: 22 p. + 12 figures (1 compressed Ps-file), DESY 94-124 figure file
replaced by uuencoded fil
Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD
With the H1 detector at the ep collider HERA, D* meson production cross
sections have been measured in deep inelastic scattering with four-momentum
transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88
GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe
the differential cross sections within theoretical and experimental
uncertainties. Using these calculations, the NLO gluon momentum distribution in
the proton, x_g g(x_g), has been extracted in the momentum fraction range
7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon
momentum fraction x_g has been obtained from the measured kinematics of the
scattered electron and the D* meson in the final state. The results compare
well with the gluon distribution obtained from the analysis of scaling
violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
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