389 research outputs found
Relentless increase of resistance to fluoroquinolones and expanded-spectrum cephalosporins in Escherichia coli: 20 years of surveillance in resource-limited settings from Latin America.
AbstractPrevious studies on commensal Escherichia coli from healthy children in the Bolivian Chaco have shown remarkable resistance rates to the old antibiotics since the early 1990s, and the emergence of resistance to newer drugs (fluoroquinolones and expanded-spectrum cephalosporins) in the 2000s. Here we report the results of a new survey conducted in 2011 in the same setting. Rectal swabs were obtained from 482 healthy children (aged 6â72 months) from three urban areas of the Bolivian Chaco. Screening for antibiotic-resistant E. coli was performed by a direct plating method, as in the previous studies. The blaCTX-M genes were investigated by PCR/sequencing, and CTX-M-producing isolates were subjected to genotyping and detection of several plasmid-mediated quinolone resistance mechanisms. Results showed high rates of resistance to nalidixic acid (76%), ciprofloxacin (44%) and expanded-spectrum cephalosporins (12.4%), demonstrating a relentless increase of resistance to those drugs over the past two decades. CTX-M-type extended-spectrum beta-lactamases were found to be widespread (12%, 97% of extended-spectrum beta-lactamase producers). Compared with the previous studies, CTX-M-producing E. coli underwent a dramatic dissemination (120-fold increase since early 2000s) and a radical change of dominant CTX-M groups (CTX-M-1 and CTX-M-9 groups versus CTX-M-2 group). Most CTX-M producers were not susceptible to quinolones (91%), and 55% carried plasmid-mediated quinolone resistance genes (different combinations of aac(6')-Ib-cr, qnrB and qepA). This study shows the rapid and remarkable increasing trend for resistance to fluoroquinolones and expanded-spectrum cephalosporins in one of the poorest regions of Latin America, and underscores the need for urgent control strategies aimed at preserving the efficacy of those drugs in similar settings
Massive Spin-2 States as the Origin of the Top Quark Forward-Backward Asymmetry
We show that the anomalously large top quark forward-backward asymmetry
observed by CDF and D\O\, can naturally be accommodated in models with
flavor-violating couplings of a new massive spin-2 state to quarks. Regardless
of its origin, the lowest-order couplings of a spin-2 boson to fermions are
analogous to the coupling of the graviton to energy/momentum, leading to strong
sensitivity of the effects associated with its virtual exchange to the energy
scales at hand. Precisely due to this fact, the observed dependence of the
asymmetry on the invariant mass fits nicely into the proposed
framework. In particular, we find a vast parameter space which can lead to the
central value for the observed forward-backward asymmetry in the high mass bin,
while being in accord with all of the existing experimental constraints.Comment: added discussion of differential observables at the LHC, matches
version accepted for publication in JHE
Chiral U(1) flavor models and flavored Higgs doublets: the top FB asymmetry and the Wjj
We present U(1) flavor models for leptophobic Z' with flavor dependent
couplings to the right-handed up-type quarks in the Standard Model, which can
accommodate the recent data on the top forward-backward (FB) asymmetry and the
dijet resonance associated with a W boson reported by CDF Collaboration. Such
flavor-dependent leptophobic charge assignments generally require extra chiral
fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor
symmetry calls for new U(1)'-charged Higgs doublets in order for the SM
fermions to have realistic renormalizable Yukawa couplings. The stringent
constraints from the top FB asymmetry at the Tevatron and the same sign top
pair production at the LHC can be evaded due to contributions of the extra
Higgs doublets. We also show that the extension could realize cold dark matter
candidates.Comment: 40 pages, 10 figures, added 1 figure and extended discussion,
accepted for publication in JHE
Covariant Description of Flavor Conversion in the LHC Era
A simple covariant formalism to describe flavor and CP violation in the
left-handed quark sector in a model independent way is provided. The
introduction of a covariant basis, which makes the standard model approximate
symmetry structure manifest, leads to a physical and transparent picture of
flavor conversion processes. Our method is particularly useful to derive robust
bounds on models with arbitrary mechanisms of alignment. Known constraints on
flavor violation in the K and D systems are reproduced in a straightforward
manner. Assumptions-free limits, based on top flavor violation at the LHC, are
then obtained. In the absence of signal, with 100 fb^{-1} of data, the LHC will
exclude weakly coupled (strongly coupled) new physics up to a scale of 0.6 TeV
(7.6 TeV), while at present no general constraint can be set related to Delta
t=1 processes. LHC data will constrain Delta F=2 contributions via same-sign
tops signal, with a model independent exclusion region of 0.08 TeV (1.0 TeV).
However, in this case, stronger bounds are found from the study of CP violation
in D-bar D mixing with a scale of 0.57 TeV (7.2 TeV). In addition, we apply our
analysis to models of supersymmetry and warped extra dimension. The minimal
flavor violation framework is also discussed, where the formalism allows to
distinguish between the linear and generic non-linear limits within this class
of models.Comment: 24 pages, 6 figures. Some corrections and clarifications; references
added. Matches published versio
LHC diphoton Higgs signal and top quark forward-backward asymmetry in quasi-inert Higgs doublet model
In the quasi-inert Higgs doublet model, we study the LHC diphoton rate for a
standard model-like Higgs boson and the top quark forward-backward asymmetry at
Tevatron. Taking into account the constraints from the vacuum stability,
unitarity, electroweak precision tests, flavor physics and the related
experimental data of top quark, we find that compared with the standard model
prediction, the diphoton rate of Higgs boson at LHC can be enhanced due to the
light charged Higgs contributions, while the measurement of the top quark
forward-backward asymmetry at Tevatron can be explained to within due
to the non-standard model neutral Higgs bosons contributions. Finally, the
correlations between the two observables are discussed.Comment: 14 pages, 5 figues. Version to appear in JHEP, some references adde
On the continuous CesĂ ro operator in certain function spaces
âThe final publication is available at Springer via http://dx.doi.org/10.1007/s11117-014-0321-5"Various properties of the (continuous) CesĂ ro operator C, acting on Banach
and Fréchet spaces of continuous functions and L p-spaces, are investigated. For
instance, the spectrum and point spectrum of C are completely determined and a
study of certain dynamics of C is undertaken (eg. hyper- and supercyclicity, chaotic
behaviour). In addition, the mean (and uniform mean) ergodic nature of C acting in
the various spaces is identified.The research of the first two authors was partially supported by the projects MTM2010-15200 and GVA Prometeo II/2013/013 (Spain). The second author gratefully acknowledges the support of the Alexander von Humboldt Foundation.Albanese, AA.; Bonet Solves, JA.; Ricker, WJ. (2015). On the continuous CesĂ ro operator in certain function spaces. Positivity. 19:659-679. https://doi.org/10.1007/s11117-014-0321-5S65967919Albanese, A.A.: Primary products of Banach spaces. Arch. Math. 66, 397â405 (1996)Albanese, A.A.: On subspaces of the spaces L loc p and of their strong duals. Math. Nachr. 197, 5â18 (1999)Albanese, A.A., Moscatelli, V.B.: Complemented subspaces of sums and products of copies of L 1 [ 0 , 1 ] . Rev. Mat. Univ. Complut. Madr. 9, 275â287 (1996)Albanese, A.A., Bonet, J., Ricker, W.J.: Mean ergodic operators in FrĂ©chet spaces. Ann. Acad. Sci. Fenn. Math. 34, 401â436 (2009)Albanese, A.A., Bonet, J., Ricker, W.J.: On mean ergodic operators. In: Curbera, G.P. (eds.) Vector Measures, Integration and Related Topics. Operator Theory: Advances and Applications, vol. 201, pp. 1â20. BirkhĂ€user, Basel (2010)Albanese, A.A., Bonet, J., Ricker, W.J.: C 0 -semigroups and mean ergodic operators in a class of FrĂ©chet spaces. J. Math. Anal. Appl. 365, 142â157 (2010)Albanese, A.A., Bonet, J., Ricker, W.J.: Convergence of arithmetic means of operators in FrĂ©chet spaces. J. Math. Anal. Appl. 401, 160â173 (2013)Bayart, F., Matheron, E.: Dynamics of linear operators. Cambridge Tracts in Mathematics, vol. 179. Cambridge University Press, Cambridge (2009)Bellenot, S.F., Dubinsky, E.: FrĂ©chet spaces with nuclear Köthe quotients. Trans. Am. Math. Soc. 273, 579â594 (1982)Bonet, J., Frerick, L., Peris, A., Wengenroth, J.: Transitive and hypercyclic operators on locally convex spaces. Bull. Lond. Math. Soc. 37, 254â264 (2005)Boyd, D.W.: The spectrum of the CesĂ ro operator. Acta Sci. Math. (Szeged) 29, 31â34 (1968)Brown, A., Halmos, P.R., Shields, A.L.: CesĂ ro operators. Acta Sci. Math. (Szeged) 26, 125â137 (1965)Dierolf, S., Zarnadze, D.N.: A note on strictly regular FrĂ©chet spaces. Arch. Math. 42, 549â556 (1984)Dunford, N., Schwartz, J.T.: Linear Operators I: General Theory (2nd Printing). Wiley-Interscience, New York (1964)Galaz Fontes, F., SolĂs, F.J.: Iterating the CesĂ ro operators. Proc. Am. Math. Soc. 136, 2147â2153 (2008)Galaz Fontes, F., Ruiz-Aguilar, R.W.: Grados de ciclicidad de los operadores de CesĂ roâHardy. Misc. Mat. 57, 103â117 (2013)GonzĂĄlez, M., LeĂłn-Saavedra, F.: Cyclic behaviour of the CesĂ ro operator on L 2 ( 0 , + â ) . Proc. Am. Math. Soc. 137, 2049â2055 (2009)Grosse-Erdmann, K.G., Peris Manguillot, A.: Linear chaos. In: Universitext. Springer, London (2011)Hardy, G.H., Littlewood, J.E., PĂłlya, G.: Inequalities. In: Reprint of the 1952 Edition. Cambridge Mathematical Library. Cambridge University Press, Cambridge (1988)Krengel, U.: Ergodic theorems. In: De Gruyter Studies in Mathematics, vol. 6. Walter de Gruyter Co., Berlin (1985)Leibowitz, G.M.: Spectra of finite range CesĂ ro operators. Acta Sci. Math. (Szeged) 35, 27â28 (1973)Leibowitz, G.M.: The CesĂ ro operators and their generalizations: examples in infinite-dimensional linear analysis. Am. Math. Mon. 80, 654â661 (1973)LeĂłn-Saavedra, F., Piqueras-Lerena, A., Seoane-SepĂșlveda, J.B.: Orbits of CesĂ ro type operators. Math. Nachr. 282, 764â773 (2009)Lin, M.: On the uniform ergodic theorem. Proc. Am. Math. Soc. 43, 337â340 (1974)Meise, R., Vogt, D.: Introduction to functional analysis. In: Oxford Graduate Texts in Mathematics, vol. 2. The Clarendon Press; Oxford University Press, New York (1997)Metafune, G., Moscatelli, V.B.: Quojections and prequojections. In: TerzioÄlu, T. (ed.) Advances in the Theory of FrĂ©chet spaces. NATO ASI Series, vol. 287, pp. 235â254. Kluwer Academic Publishers, Dordrecht (1989)Moscatelli, V.B.: FrĂ©chet spaces without norms and without bases. Bull. Lond. Math. Soc. 12, 63â66 (1980)Piszczek, K.: Quasi-reflexive FrĂ©chet spaces and mean ergodicity. J. Math. Anal. Appl. 361, 224â233 (2010)Piszczek, K.: Barrelled spaces and mean ergodicity. Rev R. Acad. Cienc. Exactas Fis. Nat. Ser. A Math. RACSAM 104, 5â11 (2010)Yosida, K.: Functional Analysis, 6th edn. Springer, Berlin (1980
Discerning New Physics in Top-Antitop Production using Top Spin Observables at Hadron Colliders
Copious production of top-antitop quark pairs at hadron colliders has enabled
various probes into the properties and interactions of top quarks. Among the
various presently measured observables, the forward-backward asymmetry (FBA) in
t tbar production measured at the Tevatron significantly deviates from the
standard model predictions, and many models of new physics have been invented
to explain the puzzle. We consider the consistency of the simplified
single-resonance models containing a color octet axial-vector ("axigluon"),
color triplet or sextet weak singlet scalars, weak isodoublet scalar,
flavor-changing neutral Z', or charged W' vector boson with existing t tbar
production measurements. Among the considered models only an axigluon can
reproduce all Tevatron observables, without being in severe tension with the
recent LHC results on t tbar production cross section, charge asymmetry and
top-spin correlations. The LHC charge asymmetry measurements exclude the W' and
Z' explanations of the Tevatron FBA anomaly. On the other hand, all scalar
models predict notable deviations in several top spin observables, and the
recent top spin correlation measurement using the "helicity" spin quantization
axis by ATLAS already provides a significant constraint on possible
explanations of the Tevatron FBA anomaly. Future precise measurements of top
spin correlations and especially top polarization could differentiate between
scalar t(u)-channel models, while they are less sensitive to pure axigluon
contributions.Comment: 22 pages, 8 figures, published versio
Field redefinitions in effective theories at higher orders
The invariance of physical observables under redefinitions of the quantum fields
is a well-known and important property of quantum field theory. We study perturbative field redefinitions in effective theories, paying special attention to higher-order effects and
their impact on matching to an ultraviolet theory at the classical and quantum levels.Our
work has been supported by the Spanish MINECO project FPA2016-78220-C3-1-P (Fondos
FEDER) and the Junta de AndalucĂa grant FQM101. The work of J.C.C. has also been
supported by the Spanish MECD grant FPU14
Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV
The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of âs = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pTâ„20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60â€pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2â€{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
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