365 research outputs found
Towards a four-loop form factor
The four-loop, two-point form factor contains the first non-planar correction
to the lightlike cusp anomalous dimension. This anomalous dimension is a
universal function which appears in many applications. Its planar part in N = 4
SYM is known, in principle, exactly from AdS/CFT and integrability while its
non-planar part has been conjectured to vanish. The integrand of the form
factor of the stress-tensor multiplet in N = 4 SYM including the non-planar
part was obtained in previous work. We parametrise the difficulty of
integrating this integrand. We have obtained a basis of master integrals for
all integrals in the four-loop, two-point class in two ways. First, we computed
an IBP reduction of the integrand of the N = 4 form factor using massive
computer algebra (Reduze). Second, we computed a list of master integrals based
on methods of the Mint package, suitably extended using Macaulay2 / Singular.
The master integrals obtained in both ways are consistent with some minor
exceptions. The second method indicates that the master integrals apply beyond
N = 4 SYM, in particular to QCD. The numerical integration of several of the
master integrals will be reported and remaining obstacles will be outlinedComment: 9 Pages, Radcor/Loopfest 2015 Proceeding
Master integrals for the four-loop Sudakov form factor
The light-like cusp anomalous dimension is a universal function in the
analysis of infrared divergences. In maximally () supersymmetric
Yang-Mills theory (SYM) in the planar limit, it is known, in principle, to all
loop orders. The non-planar corrections are not known in any theory, with the
first appearing at the four-loop order. The simplest quantity which contains
this correction is the four-loop two-point form factor of the stress tensor
multiplet. This form factor was largely obtained in integrand form in a
previous work for SYM, up to a free parameter. In this work, a
reduction of the appearing integrals obtained by solving integration-by-parts
(IBP) identities using a modified version of Reduze is reported. The form
factor is shown to be independent of the remaining parameter at integrand level
due to an intricate pattern of cancellations after IBP reduction. Moreover, two
of the integral topologies vanish after reduction. The appearing master
integrals are cross-checked using independent algebraic-geometry techniques
explored in the Mint package. The latter results provide the basis of master
integrals applicable to generic form factors, including those in Quantum
Chromodynamics. Discrepancies between explicitly solving the IBP relations and
the MINT approach are highlighted. Remaining bottlenecks to completing the
computation of the four-loop non-planar cusp anomalous dimension in
SYM and beyond are identified.Comment: 42 pages, 4 tables, 4 ancillary files, matches journal versio
On-shell supersymmetry for massive multiplets
The consequences of on-shell supersymmetry are studied for scattering
amplitudes with massive particles in four dimensions. Using the massive version
of the spinor helicity formalism the supersymmetry transformations relating
products of on-shell states are derived directly from the on-shell
supersymmetry algebra for any massive representation. Solutions to the
resulting Ward identities can be constructed as functions on the on-shell
superspaces that are obtained from the coherent state method. In simple cases
it is shown that these superspaces allow one to construct explicitly
supersymmetric scattering amplitudes. Supersymmetric on-shell recursion
relations for tree-level superamplitudes with massive particles are introduced.
As examples, simple supersymmetric amplitudes are constructed in SQCD, the
Abelian Higgs model, the Coulomb branch of N=4 super Yang-Mills, QCD with an
effective Higgs-gluon coupling and for massive vector boson currents.Comment: 49+9 pages, 4 figures, v2: references updated, typos corrected,
examples added, v3: final PRD versio
MHV, CSW and BCFW: field theory structures in string theory amplitudes
Motivated by recent progress in calculating field theory amplitudes, we study
applications of the basic ideas in these developments to the calculation of
amplitudes in string theory. We consider in particular both non-Abelian and
Abelian open superstring disk amplitudes in a flat space background, focusing
mainly on the four-dimensional case. The basic field theory ideas under
consideration split into three separate categories. In the first, we argue that
the calculation of alpha'-corrections to MHV open string disk amplitudes
reduces to the determination of certain classes of polynomials. This line of
reasoning is then used to determine the alpha'^3-correction to the MHV
amplitude for all multiplicities. A second line of attack concerns the
existence of an analog of CSW rules derived from the Abelian Dirac-Born-Infeld
action in four dimensions. We show explicitly that the CSW-like perturbation
series of this action is surprisingly trivial: only helicity conserving
amplitudes are non-zero. Last but not least, we initiate the study of BCFW
on-shell recursion relations in string theory. These should appear very
naturally as the UV properties of the string theory are excellent. We show that
all open four-point string amplitudes in a flat background at the disk level
obey BCFW recursion relations. Based on the naturalness of the proof and some
explicit results for the five-point gluon amplitude, it is expected that this
pattern persists for all higher point amplitudes and for the closed string.Comment: v3: corrected erroneous statement about Virasoro-Shapiro amplitude
and added referenc
Three particle superstring amplitudes with massive legs
On-shell superspaces and associated spinor helicity techniques give an
efficient formulation of the Ward identities of on-shell supersymmetry for
scattering amplitudes and supply tools to construct their solutions. Based on
these techniques in this paper the general solutions of the Ward identities are
presented for three particle scattering amplitudes with one, two or three
massive legs for simple supersymmetry in ten and eight dimensions. It is shown
in examples how these solutions may be used to obtain concrete amplitudes for
the closed (IIB) and open superstring in a flat background. Explicit results
include all three point amplitudes with one massive leg whose functional form
is shown to be dictated completely by super-Poincare symmetry. The resulting
surprisingly simple series only involves massive superfields labelled by
completely symmetric little group representations. The extension to more
general explicit three and higher point amplitudes in string theory is
initiated. In appendices the field content of the fundamental massive
superfields of the open and closed superstring are listed in terms of the
Dynkin labels of a variety of groups which may be of independent interest.Comment: 45 pages. v2: typos corrected, references adde
Tests immunochromatographiques : faux positifs à la méthadone et à la phencyclidine en relation avec une intoxication par tramadol et dextropropoxyphène
Date du colloque : 10/2009</p
Metformin overdose: A serious iatrogenic complication-Western France Poison Control Centre Data Analysis
INTRODUCTION: The prevalence of type 2 diabetes (T2D) continues to rise across the world. Metformin is still considered the "gold standard" and is, therefore, increasingly prescribed. Monitoring of metformin continues to be debated because of its association with lactic acidosis (MALA), a rare but life-threatening complication. The aim of this study was to identify the main individual characteristics associated with severe poisoning in self-poisonings and therapeutic accidents reported at the Western France Poison Control Centre (PCC).
METHODS: Retrospective study of metformin poisoning from September 1999 to September 2016 at the Western France PCC recorded in the French PCC\u27s database (SICAP). The end-point was clinically high severity (mortality and/or cardiovascular shock and/or GCS ≤ 7/15).
RESULTS: Of the 382 cases included, 197 concerned acute accidental exposures, 127 self-poisonings and 58 therapeutic accidents. MALA concerned 63 patients: 44 therapeutic accidents and 19 self-poisonings. High severity concerned 59 patients: 47 therapeutic accidents and 12 self-poisonings. T2D and age > 60 significantly increase the risk of high severity (OR 7.7, CI [1.54-38.41]; P = 0.013; OR 3.5, CI [1.60-7.84]; P = 0.002, respectively).
CONCLUSIONS: Metformin may lead to MALA and severe poisoning in therapeutic accidents but also in self-poisoning circumstances. Among reported cases, T2D history and age >60 increase the risk of serious poisoning. Monitoring of their treatment should be taken seriously especially in the event of digestive symptoms such as diarrhoea
Symmetries of the Self-Dual Sector of N=4 Super Yang-Mills on the Light Cone
A recent paper proposes a way of constructing infinite dimensional symmetries
of the non-supersymmetric self-dual Yang-Mills action using isometries of the
space-time. We review the Lagrangian formulation of N = 4 super Yang-Mills MHV
rules and extend the approach taken for the non-supersymmetric case to
construct infinite dimensional symmetries of self-dual N = 4 super Yang-Mills.Comment: 22 pages, 8 figures. V[2] Added references and minor typographical
correction
On correlation functions of Wilson loops, local and non-local operators
We discuss and extend recent conjectures relating partial null limits of
correlation functions of local gauge invariant operators and the expectation
value of null polygonal Wilson loops and local gauge invariant operators. We
point out that a particular partial null limit provides a strategy for the
calculation of the anomalous dimension of short twist-two operators at weak and
strong coupling.Comment: 29 pages, 8 figure
Supersymmetric Gauge Theories in Twistor Space
We construct a twistor space action for N=4 super Yang-Mills theory and show
that it is equivalent to its four dimensional spacetime counterpart at the
level of perturbation theory. We compare our partition function to the original
twistor-string proposal, showing that although our theory is closely related to
string theory, it is free from conformal supergravity. We also provide twistor
actions for gauge theories with N<4 supersymmetry, and show how matter
multiplets may be coupled to the gauge sector.Comment: 23 pages, no figure
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