1,226 research outputs found
SMEFiT: a flexible toolbox for global interpretations of particle physics data with effective field theories
The Standard Model Effective Field Theory (SMEFT) provides a robust framework
to interpret experimental measurements in the context of new physics scenarios
while minimising assumptions on the nature of the underlying UV-complete
theory. We present the Python open source SMEFiT framework, designed to carry
out parameter inference in the SMEFT within a global analysis of particle
physics data. SMEFiT is suitable for inference problems involving a large
number of EFT degrees of freedom, without restrictions on their functional
dependence in the fitted observables, can include UV-inspired restrictions in
the parameter space, and implements arbitrary rotations between operator bases.
Posterior distributions are determined from two complementary approaches,
Nested Sampling and Monte Carlo optimisation. SMEFiT is released together with
documentation, tutorials, and post-analysis reporting tools, and can be used to
carry out state-of-the-art EFT fits of Higgs, top quark, and electroweak
production data. To illustrate its functionalities, we reproduce the results of
the recent ATLAS EFT interpretation of Higgs and electroweak data from Run II
and demonstrate how equivalent results are obtained in two different operator
bases.Comment: 19 pages, 5 figures. The smefit framework is available from
https://github.com/LHCfitNikhef/smefit_releas
Bayesian Approach to Inverse Problems: an Application to NNPDF Closure Testing
We discuss the Bayesian approach to the solution of inverse problems and
apply the formalism to analyse the closure tests performed by the NNPDF
collaboration. Starting from a comparison with the approach that is currently
used for the determination of parton distributions (PDFs) by the NNPDF
collaboration, we discuss some analytical results that can be obtained for
linear problems and use these results as a guidance for the more complicated
non-linear problems. We show that, in the case of Gaussian distributions, the
posterior probability density of the parametrized PDFs is fully determined by
the results of the NNPDF fitting procedure. In the particular case that we
consider, the fitting procedure and the Bayesian analysis yield exactly the
same result. Building on the insight that we obtain from the analytical
results, we introduce new estimators to assess the statistical faithfulness of
the fit results in closure tests. These estimators are defined in data space,
and can be studied analytically using the Bayesian formalism in a linear model
in order to clarify their meaning. Finally we present numerical results from a
number of closure tests performed with current NNPDF methodologies. These
further tests allow us to validate the NNPDF4.0 methodology and provide a
quantitative comparison of the NNPDF4.0 and NNPDF3.1 methodologies. As PDFs
determinations move into precision territory, the need for a careful validation
of the methodology becomes increasingly important: the error bar has become the
focal point of contemporary PDFs determinations. In this perspective,
theoretical assumptions and other sources of error are best formulated and
analysed in the Bayesian framework, which provides an ideal language to address
the precision and the accuracy of current fits
Notes on lattice observables for parton distributions:nongauge theories
We review recent theoretical developments concerning the definition and the
renormalization of equal-time correlators that can be computed on the lattice
and related to Parton Distribution Functions (PDFs) through a factorization
formula. We show how these objects can be studied and analyzed within the
framework of a nongauge theory, gaining insight through a one-loop computation.
We use scalar field theory as a playground to revise, analyze and present the
main features of these ideas, to explore their potential, and to understand
their limitations for extracting PDFs. We then propose a framework that would
allow to include the available lattice QCD data in a global analysis to extract
PDFs.Comment: 20 pages, 2 figure
On the positivity of MSbar parton distributions
We revisit our argument that shows that parton distribution Functions (PDFs)
in the MSbar{ scheme are non-negative in the perturbative region, with the main
goals of elucidating its domain of validity and clarifying its theoretical
underpinnings. We specifically discuss recent results proving that PDFs can
turn negative at sufficiently low scale, we clarify quantitatively various
aspects of our derivation of positivity in the perturbative region, and we
provide an estimate for the scale above which PDF positivity holds
Parton distributions from lattice data:the nonsinglet case
We revise the relation between Parton Distribution Functions (PDFs) and
matrix elements computable from lattice QCD, focusing on the quasi-Parton
Distribution Functions (qPDFs) approach. We exploit the relation between PDFs
and qPDFs in the case of the unpolarized isovector parton distribution to
obtain a factorization formula relating the real and imaginary part of qPDFs
matrix elements to specific nonsinglet distributions, and we propose a general
framework to extract PDFs from the available lattice data, treating them on the
same footing as experimental data. We implement the proposed approach within
the NNPDF framework, and we study the potentiality of such lattice data in
constraining PDFs, assuming some plausible scenarios to assess the unknown
systematic uncertainties. We finally extract the two nonsinglet distributions
involved in our analysis from a selection of the available lattice data.Comment: 26 pages, 7 figures; added references, corrected typo
In vivo emergence of colistin resistance in Klebsiella pneumoniae producing KPC-type carbapenemases mediated by insertional inactivation of the PhoQ/PhoP mgrB regulator
Colistin is one of the few agents that retain activity against extensively drug-resistant strains of Klebsiella pneumoniae producing KPC-type carbapenemases (KPC-KP). However, resistance to colistin is increasingly reported among KPC-KP. Comparative genomic analysis of a pair of sequential KPC-KP isolates from the same patient including a colistin-susceptible isolate (KKBO-1) and a colistin-resistant isolate (KKBO-4) selected after colistin exposure revealed that insertional inactivation of the mgrB gene, encoding a negative regulator of the PhoQ/PhoP signaling system, is a genetic mechanism for acquired colistin resistance. The role of mgrB inactivation in acquired colistin resistance was confirmed by complementation experiments with wild-type mgrB, which restored colistin susceptibility in KKBO-4, and by construction of an mgrB deletion mutant from KKBO-1, which exhibited a colistin-resistant phenotype. Insertional mgrB inactivation was also detected in 60% of colistin-resistant mutants selected from KKBO-1 in vitro, following plating on colistin-containing medium, confirming the role (although not unique) of this mechanism in the emergence of acquired colistin resistance. In colistin-resistant mutants carrying insertional inactivation or deletion of the mgrB gene, upregulated transcription of phoP, phoQ, and pmrK (which is part of the pmrHFIJKLM operon) was detected. These findings confirmed the MgrB regulatory role in K. pneumoniae and were in agreement with the known association between upregulation of the PhoQ/PhoP system and activation of the pmrHFIJKLM operon, which eventually leads to resistance to polymyxins by modification of the lipopolysaccharide target
Draft genome sequence of Proteus mirabilis NO-051/ 03, representative of a multidrug-resistant clone spreading in Europe and expressing the CMY-16 AmpC-type β-lactamase
Proteus mirabilis NO-051/03, representative of a multidrug-resistant clone expressing the CMY-16 AmpC-type β-lactamase and circulating in Europe since 2003, was sequenced by a MiSeq platform using a paired-end approach. The genome was assembled in 100 scaffolds with a total length of 4,197,318 bp. Analysis of the draft genome sequence revealed the presence of several acquired resistance determinants to β-lactams, aminoglycosides, phenicols, tetracyclines, trimethoprim, and sulfonamides, of one plasmid replicon, and of a type I-E clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein (Cas) adaptive immune system
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