233 research outputs found
From correlation functions to scattering amplitudes
We study the correlators of half-BPS protected operators in N=4
super-Yang-Mills theory, in the limit where the positions of the adjacent
operators become light-like separated. We compute the loop corrections by means
of Lagrangian insertions. The divergences resulting from the light-cone limit
are regularized by changing the dimension of the integration measure over the
insertion points. Switching from coordinates to dual momenta, we show that the
logarithm of the correlator is identical with twice the logarithm of the
matching MHV gluon scattering amplitude. We present a number of examples of
this new relation, at one and two loops.Comment: typos corrected, references adde
OPE for Super Loops
We extend the Operator Product Expansion for Null Polygon Wilson loops to the
Mason-Skinner-Caron-Huot super loop, dual to non MHV gluon amplitudes. We
explain how the known tree level amplitudes can be promoted into an infinite
amount of data at any loop order in the OPE picture. As an application, we
re-derive all one loop NMHV six gluon amplitudes by promoting their tree level
expressions. We also present some new all loops predictions for these
amplitudes.Comment: 16 pages + appendices; 5 figure
On soft singularities at three loops and beyond
We report on further progress in understanding soft singularities of massless
gauge theory scattering amplitudes. Recently, a set of equations was derived
based on Sudakov factorization, constraining the soft anomalous dimension
matrix of multi-leg scattering amplitudes to any loop order, and relating it to
the cusp anomalous dimension. The minimal solution to these equations was shown
to be a sum over color dipoles. Here we explore potential contributions to the
soft anomalous dimension that go beyond the sum-over-dipoles formula. Such
contributions are constrained by factorization and invariance under rescaling
of parton momenta to be functions of conformally invariant cross ratios.
Therefore, they must correlate the color and kinematic degrees of freedom of at
least four hard partons, corresponding to gluon webs that connect four eikonal
lines, which first appear at three loops. We analyze potential contributions,
combining all available constraints, including Bose symmetry, the expected
degree of transcendentality, and the singularity structure in the limit where
two hard partons become collinear. We find that if the kinematic dependence is
solely through products of logarithms of cross ratios, then at three loops
there is a unique function that is consistent with all available constraints.
If polylogarithms are allowed to appear as well, then at least two additional
structures are consistent with the available constraints.Comment: v2: revised version published in JHEP (minor corrections in Sec. 4;
added discussion in Sec. 5.3; refs. added); v3: minor corrections (eqs. 5.11,
5.12 and 5.29); 38 pages, 3 figure
The cusp anomalous dimension at three loops and beyond
We derive an analytic formula at three loops for the cusp anomalous dimension
Gamma_cusp(phi) in N=4 super Yang-Mills. This is done by exploiting the
relation of the latter to the Regge limit of massive amplitudes. We comment on
the corresponding three loops quark anti-quark potential. Our result also
determines a considerable part of the three-loop cusp anomalous dimension in
QCD. Finally, we consider a limit in which only ladder diagrams contribute to
physical observables. In that limit, a precise agreement with strong coupling
is observed.Comment: 34 pages, 6 figures. v2: references added, typos correcte
Cultural robotics : The culture of robotics and robotics in culture
Copyright 2013 Samani et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedIn this paper, we have investigated the concept of "Cultural Robotics" with regard to the evolution o social into cultural robots in the 21st Century. By defining the concept of culture, the potential development of culture between humans and robots is explored. Based on the cultural values of the robotics developers, and the learning ability of current robots, cultural attributes in this regard are in the process of being formed, which would define the new concept of cultural robotics. According to the importance of the embodiment of robots in the sense of presence, the influence of robots in communication culture is anticipated. The sustainability of robotics culture based on diversity for cultural communities for various acceptance modalities is explored in order to anticipate the creation of different attributes of culture between robot and humans in the futurePeer reviewe
From correlation functions to Wilson loops
We start with an n-point correlation function in a conformal gauge theory. We
show that a special limit produces a polygonal Wilson loop with sides. The
limit takes the points towards the vertices of a null polygonal Wilson loop
such that successive distances . This produces a fast moving
particle that generates a "frame" for the Wilson loop. We explain in detail how
the limit is approached, including some subtle effects from the propagation of
a fast moving particle in the full interacting theory. We perform perturbative
checks by doing explicit computations in N=4 super-Yang-Mills.Comment: 37 pages, 10 figures; typos corrected, references adde
Post-Kala-azar Dermal Leishmaniasis in Nepal: A Retrospective Cohort Study (2000–2010)
Post-kala-azar dermal leishmaniasis (PKDL) is a skin disorder seen in patients treated for Leishmania donovani visceral leishmaniasis (VL), a neglected tropical disease that is fatal if left untreated. In the Indian subcontinent, PKDL is seen in 5–10% of all past VL cases and is also reported in some without history of VL. As persons with PKDL do not feel sick, the disease has only cosmetic significance for the individual and treatment is rarely sought. However, PKDL lesions harbour parasites and therefore could represent a source of transmission, through the bite of female sand flies. Our study shows that the occurrence of PKDL in patients with past treated VL is low in Nepal compared to neighboring countries. Treatment of the original VL episode with SSG (sodium stibogluconate), inadequate treatment and treatment on ambulatory basis were significantly associated with PKDL. Though SSG has since been replaced by other drugs, counseling and supervision of adherence to the prescribed VL treatment is of vital importance to reduce risk of treatment failure and relapse as well as later development of PKDL. Policy makers should include surveillance and case management of PKDL in the VL elimination program
M5-branes from gauge theories on the 5-sphere
We use the 5-sphere partition functions of supersymmetric Yang-Mills theories
to explore the (2,0) superconformal theory on S^5 x S^1. The 5d theories can be
regarded as Scherk-Schwarz reductions of the 6d theory along the circle. In a
special limit, the perturbative partition function takes the form of the
Chern-Simons partition function on S^3. With a simple non-perturbative
completion, it becomes a 6d index which captures the degeneracy of a sector of
BPS states as well as the index version of the vacuum Casimir energy. The
Casimir energy exhibits the N^3 scaling at large N. The large N index for U(N)
gauge group also completely agrees with the supergravity index on AdS_7 x S^4.Comment: 44 pages, 1 figure, v4: ref added, clarified weak/strong coupling
behaviors of large N free energy, minor improvements, version to be published
in JHE
Nitroheterocyclic drugs cure experimental <i>Trypanosoma cruzi</i> infections more effectively in the chronic stage than in the acute stage
The insect-transmitted protozoan parasite Trypanosoma cruzi is the causative agent of Chagas disease, and infects 5-8 million people in Latin America. Chagas disease is characterised by an acute phase, which is partially resolved by the immune system, but then develops as a chronic life-long infection. There is a consensus that the front-line drugs benznidazole and nifurtimox are more effective against the acute stage in both clinical and experimental settings. However, confirmative studies have been restricted by difficulties in demonstrating sterile parasitological cure. Here, we describe a systematic study of nitroheterocyclic drug efficacy using highly sensitive bioluminescence imaging of murine infections. Unexpectedly, we find both drugs are more effective at curing chronic infections, judged by treatment duration and therapeutic dose. This was not associated with factors that differentially influence plasma drug concentrations in the two disease stages. We also observed that fexinidazole and fexinidazole sulfone are more effective than benznidazole and nifurtimox as curative treatments, particularly for acute stage infections, most likely as a result of the higher and more prolonged exposure of the sulfone derivative. If these findings are translatable to human patients, they will have important implications for treatment strategies
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