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- Biblioteca Digital da Unicamp
- National Academy of Sciences
- Universidade Federal de Uberlândia
- Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto
- Springer Berlin Heidelberg
- Genetics Society of America
- Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
- Universidade Cornell
- Institute of Physics
- Nature Preceedings
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Resultados filtrados por Publicador: Universidade Cornell

## LHAPDF: PDF Use from the Tevatron to the LHC

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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Parton Density Functions (PDFs) and their uncertainties are extremely
important topics for both the Tevatron and the LHC. Experiments at the Tevatron
can enhance this knowledge not only by constraining the PDF fits, but also by
developing and refining the available PDF tools through feed-back from the
experiments that are currently analyzing the highest energy hadron collider
data available. It is important that the community has standardized tools and
methods at its disposal. In this note we summarize briefly the most recent
developments of the The Les Houches Accord PDF (LHAPDF), which is the modern
replacement for PDFLIB. We also outline and compare the methods of quantifying
the impact of PDF uncertainties on physical observables. The PDF weighting
method for propagating errors from PDFs to event generator observables is
outlined in detail, and example code for using this method with PYTHIA is also
included.; Comment: 8 pages, 2 figures, 2 tables; prepared for the TeV4LHC workshop; v2 -
reference added

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## ManeParse: Mathematica Toolbox for PDF Uncertainties and Application to New Physics Searches

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/10/2015
Português

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As the LHC begins Run 2 at an even higher energy, one of the top priorities
will be to search for new particles (possibly from SUSY) at the highest energy
scales. In addition to direct production of new particles, they can mix with
Standard Model (SM) particles to yield discrepancies from the usual
predictions. To distinguish this new physics from old uncertainties, we need
tools to precisely quantify the uncertainties of the SM predictions. Here we
present a versatile set of utility functions built with Mathematica that is
capable of working with a variety of PDF formats including the recent LHAPDF6
format.
This software can perform PDF calculations within the Mathematica framework
and compare results from different PDF collaborations. The package includes
both the central PDF value as well as the full error sets needed for PDF
uncertainty analysis; a variety of sample error definitions are implemented. We
demonstrate this package for the case of a new heavy scalar particle production
at the LHC.; Comment: 5 pages, 11 figures, Presentation at the DPF 2015 Meeting of the
American Physical Society Division of Particles and Fields, Ann Arbor,
Michigan, August 4-8, 2015

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## The Atacama Cosmology Telescope: A Measurement of the Thermal Sunyaev-Zel'dovich One-Point PDF

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/11/2014
Português

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We present a measurement of the one-point probability distribution function
(PDF) of the thermal Sunyaev-Zel'dovich (tSZ) decrement in the pixel
temperature histogram of filtered 148 GHz sky maps from the Atacama Cosmology
Telescope (ACT). The PDF includes the signal from all galaxy clusters in the
map, including objects below the signal-to-noise threshold for individual
detection, making it a particularly sensitive probe of the amplitude of matter
density perturbations, $\sigma_8$. We use a combination of analytic halo model
calculations and numerical simulations to compute the theoretical tSZ PDF and
its covariance matrix, accounting for all noise sources and including
relativistic corrections. From the measured ACT 148 GHz PDF alone, we find
$\sigma_8 = 0.793 \pm 0.018$, with additional systematic errors of $\pm 0.017$
due to uncertainty in intracluster medium gas physics and $\pm 0.006$ due to
uncertainty in infrared point source contamination. Using effectively the same
data set, the statistical error here is a factor of two lower than that found
in ACT's previous $\sigma_8$ determination based solely on the skewness of the
tSZ signal. In future temperature maps with higher sensitivity, the tSZ PDF
will break the degeneracy between intracluster medium gas physics and
cosmological parameters.; Comment: 29 pages...

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## Theory of the 1-point PDF for incompressible Navier-Stokes fluids

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 01/10/2009
Português

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Fundamental aspects of fluid dynamics are related to construction of
statistical models for incompressible Navier-Stokes fluids. The latter can be
considered either \textit{deterministic} or \textit{stochastic,} respectively
for \textit{regular} or \textit{turbulent flows.} In this work we claim that a
possible statistical formulation of this type can be achieved by means of the
1-point (local) velocity-space probability density function (PDF, $f_{1}$) to
be determined in the framework of the so-called inverse kinetic theory (IKT).
There are several important consequences of the theory. These include, in
particular, the characterization of the initial PDF [for the statistical model
${f_{1},\Gamma} ]$ . This is found to be generally non-Gaussian PDF, even in
the case of flows which are regular at the initial time. Moreover, both for
regular and turbulent flows, its time evolution is provided by a Liouville
equation, while the corresponding Liouville operator is found to depend only on
a finite number of velocity moments of the same PDF. Hence, its time evolution
depends (functionally) solely on the same PDF. In addition, the statistical
model here developed determines uniquely both the initial condition and the
time evolution of $f_{1}.$ As a basic implication...

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## A non-hybrid method for the PDF equations of turbulent flows on unstructured grids

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/06/2010
Português

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In probability density function (PDF) methods of turbulent flows, the joint
PDF of several flow variables is computed by numerically integrating a system
of stochastic differential equations for Lagrangian particles. A set of
parallel algorithms is proposed to provide an efficient solution of the PDF
transport equation, modeling the joint PDF of turbulent velocity, frequency and
concentration of a passive scalar in geometrically complex configurations. An
unstructured Eulerian grid is employed to extract Eulerian statistics, to solve
for quantities represented at fixed locations of the domain (e.g. the mean
pressure) and to track particles. All three aspects regarding the grid make use
of the finite element method (FEM) employing the simplest linear FEM shape
functions. To model the small-scale mixing of the transported scalar, the
interaction by exchange with the conditional mean model is adopted. An adaptive
algorithm that computes the velocity-conditioned scalar mean is proposed that
homogenizes the statistical error over the sample space with no assumption on
the shape of the underlying velocity PDF. Compared to other hybrid
particle-in-cell approaches for the PDF equations, the current methodology is
consistent without the need for consistency conditions. The algorithm is tested
by computing the dispersion of passive scalars released from concentrated
sources in two different turbulent flows: the fully developed turbulent channel
flow and a street canyon (or cavity) flow. Algorithmic details on estimating
conditional and unconditional statistics...

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## PDF/A-3u as an archival format for Accessible mathematics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 23/06/2014
Português

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Including LaTeX source of mathematical expressions, within the PDF document
of a text-book or research paper, has definite benefits regarding
`Accessibility' considerations. Here we describe three ways in which this can
be done, fully compatibly with international standards ISO 32000, ISO 19005-3,
and the forthcoming ISO 32000-2 (PDF 2.0). Two methods use embedded files, also
known as `attachments', holding information in either LaTeX or MathML formats,
but use different PDF structures to relate these attachments to regions of the
document window. One uses structure, so is applicable to a fully `Tagged PDF'
context, while the other uses /AF tagging of the relevant content. The third
method requires no tagging at all, instead including the source coding as the
/ActualText replacement of a so-called `fake space'. Information provided this
way is extracted via simple Select/Copy/Paste actions, and is available to
existing screen-reading software and assistive technologies.; Comment: This is a post-print version of original in volume: S.M. Watt et al.
(Eds.): CICM 2014, LNAI 8543, pp.184-199, 2014; available at
http://link.springer.com/search?query=LNAI+8543, along with supplementary
PDF. This version, with supplement as attachment...

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## On the evolution of the density pdf in strongly self-gravitating systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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The time evolution of the probability density function (PDF) of the mass
density is formulated and solved for systems in free-fall using a simple
appoximate function for the collapse of a sphere. We demonstrate that a
pressure-free collapse results in a power-law tail on the high-density side of
the PDF. The slope quickly asymptotes to the functional form
$\mathrm{P}_v(\rho)\propto\rho^{-1.54}$ for the (volume-weighted) PDF and
$\mathrm{P}_m(\rho)\propto\rho^{-0.54}$ for the corresponding mass-weighted
distribution. From the simple approximation of the PDF we derive analytic
descriptions for mass accretion, finding that dynamically quiet systems with
narrow density PDFs lead to retarded star formation and low star formation
rates. Conversely, strong turbulent motions that broaden the PDF accelerate the
collapse causing a bursting mode of star formation. Finally, we compare our
theoretical work with observations. The measured star formation rates are
consistent with our model during the early phases of the collapse. Comparison
of observed column density PDFs with those derived from our model suggests that
observed star-forming cores are roughly in free-fall.; Comment: accepted for publication, 13 pages

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## An Upper Bound to the Marginal PDF of the Ordered Eigenvalues of Wishart Matrices

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/12/2011
Português

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Diversity analysis of a number of Multiple-Input Multiple-Output (MIMO)
applications requires the calculation of the expectation of a function whose
variables are the ordered multiple eigenvalues of a Wishart matrix. In order to
carry out this calculation, we need the marginal pdf of an arbitrary subset of
the ordered eigenvalues. In this letter, we derive an upper bound to the
marginal pdf of the eigenvalues. The derivation is based on the multiple
integration of the well-known joint pdf, which is very complicated due to the
exponential factors of the joint pdf. We suggest an alternative function that
provides simpler calculation of the multiple integration. As a result, the
marginal pdf is shown to be bounded by a multivariate polynomial with a given
degree. After a standard bounding procedure in a Pairwise Error Probability
(PEP) analysis, by applying the marginal pdf to the calculation of the
expectation, the diversity order for a number of MIMO systems can be obtained
in a simple manner. Simulation results that support the analysis are presented.; Comment: 6 pages, 2 figures

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## Constraints on the gluon PDF from top quark pair production at hadron colliders

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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Using the recently derived NNLO cross sections \cite{Czakon:2013goa}, we
provide NNLO+NNLL theoretical predictions for top quark pair production based
on all the available NNLO PDF sets, and compare them with the most precise LHC
and Tevatron data. In this comparison we study in detail the PDF uncertainty
and the scale, $m_t$ and $\alpha_s$ dependence of the theoretical predictions
for each PDF set. Next, we observe that top quark pair production provides a
powerful direct constraint on the gluon PDF at large $x$, and include Tevatron
and LHC top pair data consistently into a global NNLO PDF fit. We then explore
the phenomenological consequences of the reduced gluon PDF uncertainties, by
showing how they can improve predictions for Beyond the Standard Model
processes at the LHC. Finally, we update to full NNLO+NNLL the theoretical
predictions for the ratio of top quark cross sections between different LHC
center of mass energies, as well as the cross sections for hypothetical heavy
fourth-generation quark production at the LHC.; Comment: 29 pages, 13 figures, accepted for publication in JHEP

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