2,735 research outputs found
Integrability and maximally helicity violating diagrams in n=4 supersymmetric yang-mills theory.
We apply maximally helicity violating (MHV) diagrams to the derivation of the one-loop dilatation operator of N=4 supersymmetric Yang-Mills theory in the SO(6) sector. We find that in this approach the calculation reduces to the evaluation of a single MHV diagram in dimensional regularization. This provides the first application of MHV diagrams to an off-shell quantity. We also discuss other applications of the method and future directions
Multi - instantons, supersymmetry and topological field theories
In this letter we argue that instanton-dominated Green's functions in N=2 Super Yang-Mills theories can be equivalently computed either using the so-called constrained instanton method or making reference to the topological twisted version of the theory. Defining an appropriate BRST operator (as a supersymmetry plus a gauge variation), we also show that the expansion coefficients of the Seiberg-Witten effective action for the low-energy degrees of freedom can be written as integrals of total derivatives over the moduli space of self-dual gauge connections
Quantum MHV diagrams
Over the past two years, the use of on-shell techniques has deepened our understanding of the S-matrix of gauge theories and led to the calculation of many new scattering amplitudes. In these notes we review a particular on-shell method developed recently, the quantum MHV diagrams, and discuss applications to one-loop amplitudes. Furthermore, we briefly discuss the application of D-dimensional generalised unitarity to the calculation of scattering amplitudes in non-supersymmetric Yang-Mills
On higher-derivative effects on the gravitational potential and particle bending
Using modern amplitude techniques we compute the leading classical and
quantum corrections to the classical gravitational potential between two
massive scalars induced by adding an term to Einstein gravity. We then
study the scattering of massless scalars, photons and gravitons off a heavy
scalar in the presence of the same deformation, and determine the bending
angle in the three cases from the non-analytic component of the scattering
amplitude. Similarly to the Einstein-Hilbert case, we find that the classical
contribution to the bending angle is universal, but unlike that case,
universality is preserved also by the first quantum correction. Finally we
extend our analysis to include a deformation of the form , where
is the dilaton, which arises in the low-energy effective action of the
bosonic string in addition to the term, and compute its effect on the
graviton bending.Comment: 23 pages, 4 figures. v2: typos corrected, one reference added,
several comments and clarifications added in Section 2. v3: JHEP version. v4:
typos correcte
Ambrosia Artemisiifolia L. a Roma: una presenza non più controversa
Among the alien species reported in Latium Ambrosia artemisiifolia L. deserves special consideration because of its potential danger for allergy subjects. The spread of the species in the area is relatively recent, and it’s among those normally moni- tored by the monitoring centres in Italy and Europe. More than ten years of observations aerobiological in the city of Rome have confirmed its presence. Its concentration seems to vary in relation to precipitation occurring before the summer
Problems Affecting Labor
Much experimental work has been devoted in comparing the folding behavior of proteins sharing the same fold but different sequence. The recent design of proteins displaying very high sequence identities but different 3D structure allows the unique opportunity to address the protein-folding problem from a complementary perspective. Here we explored by ℙ-value analysis the pathways of folding of three different heteromorphic pairs, displaying increasingly high-sequence identity (namely, 30%, 77%, and 88%), but different structures called G A (a 3-α helix fold) and G B (an α/β fold). The analysis, based on 132 site-directed mutants, is fully consistent with the idea that protein topology is committed very early along the pathway of folding. Furthermore, data reveals that when folding approaches a perfect two-state scenario, as in the case of the G A domains, the structural features of the transition state appear very robust to changes in sequence composition. On the other hand, when folding is more complex and multistate, as for the G Bs, there are alternative nuclei or accessible pathways that can be alternatively stabilized by altering the primary structure. The implications of our results in the light of previous work on the folding of different members belonging to the same protein family are discussed
The SAGEX review on scattering amplitudes Chapter 1: Modern fundamentals of amplitudes
This chapter introduces the foundational elements of scattering amplitudes.
It is meant to be accessible to readers with only a basic understanding of
quantum field theory. Topics covered include: the four-dimensional
spinor-helicity formalism and the colour decomposition of Yang-Mills scattering
amplitudes; the study of soft and collinear limits of Yang-Mills and gravity
amplitudes; the BCFW recursion relation and generalised unitarity, also in the
superamplitudes formalism of supersymmetric Yang-Mills; an
overview of standard and hidden symmetries of the -matrix of
supersymmetric Yang-Mills, such as the conformal, dual
conformal and Yangian symmetries; and a brief excursus on form factors of
protected and non-protected operators in Yang-Mills theory. Several examples
and explicit calculations are also provided.Comment: 56 pages, see also the overview article arXiv:2203.1301
Structural investigation of nucleophosmin interaction with the tumor suppressor Fbw7γ
Nucleophosmin (NPM1) is a multifunctional nucleolar protein implicated in ribogenesis, centrosome duplication, cell cycle control, regulation of DNA repair and apoptotic response to stress stimuli. The majority of these functions are played through the interactions with a variety of protein partners. NPM1 is frequently overexpressed in solid tumors of different histological origin. Furthermore NPM1 is the most frequently mutated protein in acute myeloid leukemia (AML) patients. Mutations map to the C-terminal domain and lead to the aberrant and stable localization of the protein in the cytoplasm of leukemic blasts. Among NPM1 protein partners, a pivotal role is played by the tumor suppressor Fbw7γ, an E3-ubiquitin ligase that degrades oncoproteins like c-MYC, cyclin E, Notch and c-jun. In AML with NPM1 mutations, Fbw7γ is degraded following its abnormal cytosolic delocalization by mutated NPM1. This mechanism also applies to other tumor suppressors and it has been suggested that it may play a key role in leukemogenesis. Here we analyse the interaction between NPM1 and Fbw7γ, by identifying the protein surfaces implicated in recognition and key aminoacids involved. Based on the results of computational methods, we propose a structural model for the interaction, which is substantiated by experimental findings on several site-directed mutants. We also extend the analysis to two other NPM1 partners (HIV Tat and CENP-W) and conclude that NPM1 uses the same molecular surface as a platform for recognizing different protein partners. We suggest that this region of NPM1 may be targeted for cancer treatment
Integrability and unitarity
This article is distributed under the terms of the Creative Commons
Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in
any medium, provided the original author(s) and source are credited.This work was supported by the Science and Technology Facilities Council Consolidated Grant ST/L000415/1
“String theory, gauge theory & duality”
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