The Tevatron Higgs exclusion limits and theoretical uncertainties: a critical appraisal

We examine the exclusion limits set by the CDF and D0 experiments on the Standard Model Higgs boson mass from their searches at the Tevatron in the light of large theoretical uncertainties on the signal and background cross sections. We show that when these uncertainties are consistently taken into account, the sensitivity of the experiments becomes significantly lower and the currently excluded mass range $M_H=158$-175 GeV would be entirely reopened. The necessary luminosity required to recover the current sensitivity is found to be a factor of two higher than the present one.Comment: 11 pages, 5 Figures. Version published in Physics Letter B, including an erratu

The treatment of the infrared region in perturbative QCD

We discuss the contribution coming from the infrared region to NLO matrix elements and/or coefficient functions of hard QCD processes. Strictly speaking, this contribution is not known theoretically, since it is beyond perturbative QCD. For DGLAP evolution all the infrared contributions are collected in the phenomenological input parton distribution functions (PDFs), at some relatively low scale Q_0; functions which are obtained from a fit to the `global' data. However dimensional regularization sometimes produces a non-zero result coming from the infrared region. Instead of this conventional regularization treatment, we argue that the proper procedure is to first subtract from the NLO matrix element the contribution already generated at the same order in \alpha_s by the LO DGLAP splitting function convoluted with the LO matrix element. This prescription eliminates the logarithmic infrared divergence, giving a well-defined result which is consistent with the original idea that everything below Q_0 is collected in the PDF input. We quantify the difference between the proposed treatment and the conventional approach using low-mass Drell-Yan production and deep inelastic electron-proton scattering as examples; and discuss the potential impact on the `global' PDF analyses. We present arguments to show that the difference cannot be regarded as simply the use of an alternative factorization scheme.Comment: 15 pages, 5 figures, title changed, text considerably modified to improve presentation, and discussion section enlarge

Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon

There are two mechanisms for the generation of an asymmetry between the strange and anti-strange quark distributions in the nucleon: nonperturbative contributions originating from nucleons fluctuating into virtual baryon-meson pairs such as $\Lambda K$ and $\Sigma K$, and perturbative contributions arising from gluons splitting into strange and anti-strange quark pairs. While the nonperturbative contributions are dominant in the large-$x$ region, the perturbative contributions are more significant in the small-$x$ region. We calculate this asymmetry taking into account both nonperturbative and perturbative contributions, thus giving a more accurate evaluation of this asymmetry over the whole domain of $x$. We find that the perturbative contributions are generally a few times larger in magnitude than the nonperturbative contributions, which suggests that the best region to detect this asymmetry experimentally is in the region $0.02 < x < 0.03$. We find that the asymmetry may have more than one node, which is an effect that should be taken into account, e.g. for parameterizations of the strange and anti-strange quark distributions used in global analysis of parton distributions.Comment: 14 pages, 4 figures, figures comparing theoretical calculations with NNPDF global analysis added, accepted for publication in EPJ

Nuclear activity and massive star formation in the low luminosity AGN NGC4303: Chandra X-ray observations

We present evidence of the co-existence of either an AGN or an ultraluminous X-ray source (ULX), together with a young super stellar cluster in the 3 central parsecs of NGC4303. The galaxy contains a low luminosity AGN and hosts a number of starburst regions in a circumnuclear spiral, as well as in the nucleus itself. A high spatial resolution Chandra image of this source reveals that the soft X-ray emission traces the ultraviolet nuclear spiral down to a core, which is unresolved both in soft and hard X-rays. The astrometry of the X-ray core coincides with the UV core within the Chandra positioning accuracy. The total X-ray luminosity of the core, 1.5*10^{39} erg/s, is similar to that from some LINERs or from the weakest Seyferts detected so far. The soft X-rays in both the core and the extended structure surrounding it can be well reproduced by evolutionary synthesis models (which include the emission expected from single stars, the hot diffuse gas, supernova remnants and binary systems), consistent with the properties of the young stellar clusters identified in the UV. The hard X-ray tail detected in the core spectrum, however, most likely requires the presence of an additional source. This additional source could either be a weak active nucleus black hole or an ultraluminous X-ray object. The implications of these results are discussed.Comment: 37 pages, 7 figures, ApJ accepte

W boson production at hadron colliders: the lepton charge asymmetry in NNLO QCD

We consider the production of W bosons in hadron collisions, and the subsequent leptonic decay W->lnu_l. We study the asymmetry between the rapidity distributions of the charged leptons, and we present its computation up to the next-to-next-to-leading order (NNLO) in QCD perturbation theory. Our calculation includes the dependence on the lepton kinematical cuts that are necessarily applied to select W-> lnu_l events in actual experimental analyses at hadron colliders. We illustrate the main differences between the W and lepton charge asymmetry, and we discuss their physical origin and the effect of the QCD radiative corrections. We show detailed numerical results on the charge asymmetry in ppbar collisions at the Tevatron, and we discuss the comparison with some of the available data. Some illustrative results on the lepton charge asymmetry in pp collisions at LHC energies are presented.Comment: 37 pages, 21 figure

Magnetic moment of the pentaquark Θ+(1540)\Theta^+(1540) with light-cone QCD sum rules

In this article, we study the magnetic moment of the pentaquark state $\Theta^+(1540)$ as diquark-diquark-antiquark ($[ud][ud]\bar{s}$) state in the framework of the light-cone QCD sum rules approach. The numerical results indicate the magnetic moment of the pentaquark state $\Theta^+(1540)$ is about $\mu_{\Theta^+}=-(0.49\pm 0.06)\mu_N$.Comment: 10 pages, 1 figure. The main contents of this article is included in hep-ph/0503007, this article will not be submitted to a journal for publicatio

Inclusive top-pair production phenomenology with TOPIXS

We discuss various aspects of inclusive top-quark pair production based on TOPIXS, a new, flexible program that computes the production cross section at the Tevatron and LHC at next-to-next-to-leading logarithmic accuracy in soft and Coulomb resummation, including bound-state effects and the complete next-to-next-to-leading order result in the q-qbar channel, which has recently become available. We present the calculation of the top-pair cross section in pp collisions at 8 TeV centre-of-mass energy, as well as the cross sections for hypothetical heavy quarks in extensions of the standard model. The dependence on the parton distribution input is studied. Further we investigate the impact of LHC top cross section measurements at sqrt(s)=7 TeV on global fits of the gluon distribution using the NNPDF re-weighting method.Comment: 27 pages, 5 figures; v2: corrected typos in Eqs. (2.8) and (6.2) and the text, added footnote on page 4, matches published versio

QCD factorization for forward hadron scattering at high energies

We consider the QCD factorization of DIS structure functions at small x and amplitudes of 2->2 -hadronic forward scattering at high energy. We show that both collinear and k_T-factorization for these processes can be obtained approximately as reductions of a more general (totally unintegrated) form of the factorization. The requirement of ultraviolet and infrared stability of the factorization convolutions allows us to obtain restrictions on the fits for the parton distributions in k_T- and collinear factorization.Comment: 18 pages, 10 figures In the present version misprints found in the prevcious version are corrected and some more details are explaine

Advanced cell-based modeling of the royal disease: characterization of the mutated F9 mRNA

Essentials The Royal disease (RD) is a form of hemophilia B predicted to be caused by a splicing mutation. We generated an iPSC-based model of the disease allowing mechanistic studies at the RNA level. F9 mRNA analysis in iPSC-derived hepatocyte-like cells showed the predicted abnormal splicing. Mutated F9 mRNA level was very low but we also found traces of wild type transcripts. SUMMARY: Background The royal disease is a form of hemophilia B (HB) that affected many descendants of Queen Victoria in the 19th and 20th centuries. It was found to be caused by the mutation F9 c.278-3A>G. Objective To generate a physiological cell model of the disease and to study F9 expression at the RNA level. Methods Using fibroblasts from skin biopsies of a previously identified hemophilic patient bearing the F9 c.278-3A>G mutation and his mother, we generated induced pluripotent stem cells (iPSCs). Both the patient's and mother's iPSCs were differentiated into hepatocyte-like cells (HLCs) and their F9 mRNA was analyzed using next-generation sequencing (NGS). Results and Conclusion We demonstrated the previously predicted aberrant splicing of the F9 transcript as a result of an intronic nucleotide substitution leading to a frameshift and the generation of a premature termination codon (PTC). The F9 mRNA level in the patient's HLCs was significantly reduced compared with that of his mother, suggesting that mutated transcripts undergo nonsense-mediated decay (NMD), a cellular mechanism that degrades PTC-containing mRNAs. We also detected small proportions of correctly spliced transcripts in the patient's HLCs, which, combined with genetic variability in splicing and NMD machineries, could partially explain some clinical variability among affected members of the European royal families who had lifespans above the average. This work allowed the demonstration of the pathologic consequences of an intronic mutation in the F9 gene and represents the first bona fide cellular model of HB allowing the study of rare mutations at the RNA level