54 research outputs found
Double Parton Scattering Singularity in One-Loop Integrals
We present a detailed study of the double parton scattering (DPS)
singularity, which is a specific type of Landau singularity that can occur in
certain one-loop graphs in theories with massless particles. A simple formula
for the DPS singular part of a four-point diagram with arbitrary
internal/external particles is derived in terms of the transverse momentum
integral of a product of light cone wavefunctions with tree-level matrix
elements. This is used to reproduce and explain some results for DPS
singularities in box integrals that have been obtained using traditional loop
integration techniques. The formula can be straightforwardly generalised to
calculate the DPS singularity in loops with an arbitrary number of external
particles. We use the generalised version to explain why the specific MHV and
NMHV six-photon amplitudes often studied by the NLO multileg community are not
divergent at the DPS singular point, and point out that whilst all NMHV
amplitudes are always finite, certain MHV amplitudes do contain a DPS
divergence. It is shown that our framework for calculating DPS divergences in
loop diagrams is entirely consistent with the `two-parton GPD' framework of
Diehl and Schafer for calculating proton-proton DPS cross sections, but is
inconsistent with the `double PDF' framework of Snigirev.Comment: 29 pages, 8 figures. Minor corrections and clarifications added.
Version accepted for publication in JHE
Higgs production in gluon fusion at next-to-next-to-leading order QCD for finite top mass
The inclusive Higgs production cross section from gluon fusion is calculated
through NNLO QCD, including its top quark mass dependence. This is achieved
through a matching of the 1/mtop expansion of the partonic cross sections to
the exact large s-hat limits which are derived from k_T-factorization. The
accuracy of this procedure is estimated to be better than 1% for the hadronic
cross section. The final result is shown to be within 1% of the commonly used
effective theory approach, thus confirming earlier findings.Comment: 28 pages, 14 figure
From Trees to Loops and Back
We argue that generic one-loop scattering amplitudes in supersymmetric
Yang-Mills theories can be computed equivalently with MHV diagrams or with
Feynman diagrams. We first present a general proof of the covariance of
one-loop non-MHV amplitudes obtained from MHV diagrams. This proof relies only
on the local character in Minkowski space of MHV vertices and on an application
of the Feynman Tree Theorem. We then show that the discontinuities of one-loop
scattering amplitudes computed with MHV diagrams are precisely the same as
those computed with standard methods. Furthermore, we analyse collinear limits
and soft limits of generic non-MHV amplitudes in supersymmetric Yang-Mills
theories with one-loop MHV diagrams. In particular, we find a simple explicit
derivation of the universal one-loop splitting functions in supersymmetric
Yang-Mills theories to all orders in the dimensional regularisation parameter,
which is in complete agreement with known results. Finally, we present concrete
and illustrative applications of Feynman's Tree Theorem to one-loop MHV
diagrams as well as to one-loop Feynman diagrams.Comment: 52 pages, 17 figures. Some typos in Appendix A correcte
Top-mass effects in differential Higgs production through gluon fusion at order \alpha_s^4
Effects from a finite top quark mass on differential distributions in the
Higgs+jet production cross section through gluon fusion are studied at
next-to-leading order in the strong coupling, i.e. . Terms
formally subleading in are calculated, and their influence on the
transverse momentum and rapidity distribution of the Higgs boson are evaluated.
We find that, for the differential K-factor, the heavy-top limit is valid at
the 2-3% level as long as the transverse momentum of the Higgs remains below
about 150 GeV.Comment: 21 pages, 12 figure
Asymptomatic giant coronary aneurysm in an adolescent with Behcet's syndrome
<p>Abstract</p> <p>Objective</p> <p>Behcet's is an idiopathic multi-organ syndrome, which may have onset during childhood. Vascular involvement is uncommon, with rarely reported coronary aneurysm formation. We present a case report of a teenager girl who developed recalcitrant life-threatening Behcet's vasculitis, involving both small and large venous and arterial systems including a giant coronary aneurysm.</p> <p>Case report</p> <p>De-identified data were collected retrospectively in case report format. Although our sixteen year old female with Behcet's vasculitis had resolution of many arterial aneurysms, she had persistent venous thrombosis of large vessels, as well as persistent, giant arterial aneurysms requiring intra-arterial coiling of a lumbar artery and coronary bypass grafting despite intensive immunosuppression including glucocorticoids, cyclophosphamide, infliximab, methotrexate, azathioprine and intravenous immunoglobulin.</p> <p>Conclusions</p> <p>Vascular manifestations may be seen in Behcet's syndrome, including asymptomatic coronary aneurysm, which may be refractory to immunosuppression and ultimately require surgical intervention. Increased awareness is essential for prompt diagnosis and management.</p
Tree-Level Formalism
We review two novel techniques used to calculate tree-level scattering
amplitudes efficiently: MHV diagrams, and on-shell recursion relations. For the
MHV diagrams, we consider applications to tree-level amplitudes and focus in
particular on the N=4 supersymmetric formulation. We also briefly describe the
derivation of loop amplitudes using MHV diagrams. For the recursion relations,
after presenting their general proof, we discuss several applications to
massless theories with and without supersymmetry, to theories with massive
particles, and to graviton amplitudes in General Relativity. This article is an
invited review for a special issue of Journal of Physics A devoted to
"Scattering Amplitudes in Gauge Theories".Comment: 40 pages, 8 figures, invited review for a special issue of Journal of
Physics A devoted to "Scattering Amplitudes in Gauge Theories", R.
Roiban(ed), M. Spradlin(ed), A. Volovich(ed); v2: minor corrections,
references adde
European research priorities for intracerebral haemorrhage
Over 2 million people are affected by intracerebral haemorrhage (ICH) worldwide every year, one third of them dying within 1 month, and many survivors being left with permanent disability. Unlike most other stroke types, the incidence, morbidity and mortality of ICH have not declined over time. No standardised diagnostic workup for the detection of the various underlying causes of ICH currently exists, and the evidence for medical or surgical therapeutic interventions remains limited. A dedicated European research programme for ICH is needed to identify ways to reduce the burden of ICH-related death and disability. The European Research Network on Intracerebral Haemorrhage EURONICH is a multidisciplinary academic research collaboration that has been established to define current research priorities and to conduct large clinical studies on all aspects of ICH. Copyright (C) 2011 S. Karger AG, Base
THALAMIC APHASIA SYNDROME
Fall Meeting of the Belgian-Society-of-Clinical-Neurophysiology -- 34293 -- COLONSTER, BELGIUMWOS: A1994PP95800014PubMed ID: 7526590Eighteen patients (11 male, 7 female) with left thalamic haemorrhage confirmed by CT-scan of the brain were investigated for their language function. Aphasia Test for Turkish Citizens modified from Mayo Clinic Aphasia Test and Boston Diagnostic Aphasia Examination were given for evaluating the language modalities. Fluent aphasia was observed in 16 subjects (with paraphasia in 8 and hypophonia in 3). Dysarthric speech output was seen in 2 cases. Repetition and naming were well preserved while comprehension was moderately affected. This type of aphasia differs considerably from the classical aphasias and its rapid recovery is a very prominent feature.BELGIAN SOC CLIN NEUROPHYSIO
Thalamic aphasia syndrome.
PubMedID: 7526590Eighteen patients (11 male, 7 female) with left thalamic haemorrhage confirmed by CT-scan of the brain were investigated for their language function. Aphasia Test for Turkish Citizens modified from Mayo Clinic Aphasia Test and Boston Diagnostic Aphasia Examination were given for evaluating the language modalities. Fluent aphasia was observed in 16 subjects (with paraphasia in 8 and hypophonia in 3). Dysarthric speech output was seen in 2 cases. Repetition and naming were well preserved while comprehension was moderately affected. This type of aphasia differs considerably from the classical aphasias and its rapid recovery is a very prominent feature
Medial medullary infarct: Presentation of a case and terminological considerations
A case with nystagmus to ipsilateral gaze, ipsilateral tongue paralysis and contralateral corticospinal tract involvement due to medial medullary infarct on the right side is presented. This clinical picture can either be called as hypoglossal hemiplegia alternans or Jackson syndrome or, with respect to the anatomical localization of the infarct, medial medullary syndrome. The clinical application of the old and new classification is discussed
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