2,749 research outputs found
Nonperturbative contributions to a resummed leptonic angular distribution in inclusive neutral vector boson production
We present an analysis of nonperturbative contributions to the transverse
momentum distribution of bosons produced at hadron colliders. The
new data on the angular distribution of Drell-Yan pairs measured
at the Tevatron is shown to be in excellent agreement with a perturbative QCD
prediction based on the Collins-Soper-Sterman (CSS) resummation formalism at
NNLL accuracy. Using these data, we determine the nonperturbative component of
the CSS resummed cross section and estimate its dependence on arbitrary
resummation scales and other factors. With the scale dependence included at the
NNLL level, a significant nonperturbative component is needed to describe the
angular data.Comment: 36 pages, 10 figures, regular article. Revised version accepted for a
publication in Phys.Rev.
Superstring Relics, Supersymmetric Fragmentation and UHECR
Superstring theory predicts the existence of relic metastable particles whose
average lifetime is longer than the age of the universe and which could, in
principle, be good dark matter candidates. At the same time, these states would
be responsible for the Ultra High Energy Cosmic Rays (UHECR) events which will
be searched for by various experimental collaborations in the near future. We
describe a possible phenomenological path which could be followed in order to
search for new physics in their detection.Comment: 7 pages 4 Figs. Plenary Talk presented by Claudio Coriano' at the 1st
Intl. Conf. on String Phenomenology, Oxford, UK, July 6-11, 200
Double transverse-spin asymmetries in Drell--Yan and production from proton--antiproton collisions
We perform a NLO numerical study of the double transverse-spin asymmetries in
the resonance region for proton--antiproton collisions. We analyze the
large kinematic region, relevant for the proposed PAX experiment at GSI,
and discuss the implication of the results for the extraction of the
transversity densities.Comment: 8 pages, 6 figures, Talk given at "Transversity 2005" Como, Italy
7-10 Sep. 2005; eds. World Scientific in pres
Massive neutral gauge boson production as a probe of nuclear modifications of parton distributions at the LHC
We analyze the role of nuclear modifications of parton distributions,
notably, the nuclear shadowing and antishadowing corrections, in production of
lepton pairs from decays of neutral electroweak gauge bosons in proton-lead and
lead-collisions at the LHC. Using the Collins-Soper-Sterman resummation
formalism that we extended to the case of nuclear parton distributions, we
observed a direct correlation between the predicted behavior of the transverse
momentum and rapidity distributions of the produced vector bosons and the
pattern of quark and gluon nuclear modifications. This makes Drell-Yan pair
production in and collisions at the LHC a useful tool for
constraining nuclear PDFs in the small- shadowing and moderate-
antishadowing regions.Comment: 33 pages, 17 figure
Learning Ground Traversability from Simulations
Mobile ground robots operating on unstructured terrain must predict which
areas of the environment they are able to pass in order to plan feasible paths.
We address traversability estimation as a heightmap classification problem: we
build a convolutional neural network that, given an image representing the
heightmap of a terrain patch, predicts whether the robot will be able to
traverse such patch from left to right. The classifier is trained for a
specific robot model (wheeled, tracked, legged, snake-like) using simulation
data on procedurally generated training terrains; the trained classifier can be
applied to unseen large heightmaps to yield oriented traversability maps, and
then plan traversable paths. We extensively evaluate the approach in simulation
on six real-world elevation datasets, and run a real-robot validation in one
indoor and one outdoor environment.Comment: Webpage: http://romarcg.xyz/traversability_estimation
Spin and energy relaxation in germanium studied by spin-polarized direct-gap photoluminescence
Spin orientation of photoexcited carriers and their energy relaxation is
investigated in bulk Ge by studying spin-polarized recombination across the
direct band gap. The control over parameters such as doping and lattice
temperature is shown to yield high polarization degree, namely larger than 40%,
as well as a fine-tuning of the angular momentum of the emitted light with a
complete reversal between right- and left-handed circular polarization. By
combining the measurement of the optical polarization state of band-edge
luminescence and Monte Carlo simulations of carrier dynamics, we show that
these very rich and complex phenomena are the result of the electron
thermalization and cooling in the multi-valley conduction band of Ge. The
circular polarization of the direct-gap radiative recombination is indeed
affected by energy relaxation of hot electrons via the X valleys and the
Coulomb interaction with extrinsic carriers. Finally, thermal activation of
unpolarized L valley electrons accounts for the luminescence depolarization in
the high temperature regime
Investigating bias in semantic similarity measures for analysis of protein interactions
Protein interactions are fundamental blocks of almost all cellular processes, so the study of the set of protein interactions in a single organism (also referred to as Protein Interaction Networks - PIN) is an important step in the comprehension of mechanism at molecular level. Recently, the possibility to annotate such data using Gene Ontology and the consequent use of ontology-based analysis
has been exploited, e.g. the use of semantic similarity (SS) measures. Whereas, SS measures present many challenges and different issues that have to be faced. In particular SS measures are affected from three main biases: i) annotation length, ii) evidence codes, and iii) shallow annotation. The common cause of such biases are the structure of GO and the corpora of annotations (GOA). Consequently, the impact of this variability has to be considered when developing novel algorithms for protein interactions analysis. Although the criticality of these aspects, there is a lack in the systematic analysis of the bias. Few works dealt with the three sources of bias most affecting SS measures. This paper demonstrates the existence of the bias that affect main SS on a set of well-known yeast complexes. It also provides some evidences about the variability of the bias effects over the proteome
Searching for an axion-like particle at the Large Hadron Collider
Axion-like particles are an important part of the spectrum of anomalous gauge theories involving modified mechanisms of cancellation of the gauge anomalies. Among these are intersecting brane models, which are characterized by the presence of one physical axion. We overview a recent study of their supersymmetric construction and some LHC studies of the productions rates for a gauged axion
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