245 research outputs found
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
New relations for scattering amplitudes in Yang-Mills theory at loop level
The calculation of scattering amplitudes in Yang-Mills theory at loop level
is important for the analysis of background processes at particle colliders as
well as our understanding of perturbation theory at the quantum level. We
present tools to derive relations for especially one loop amplitudes, as well
as several explicit examples for gauge theory coupled to a wide variety of
matter. These tools originate in certain scaling behavior of permutation and
cyclic sums of Yang-Mills tree amplitudes and loop integrands. In the latter
case evidence exists for relations at all loop orders.Comment: 12 pages, 4 figures. v3: typos corrected, figures and clarifications
adde
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
Physical soil degradation in the Netherlands
Soils used in agriculture are subjected to a wide variety of human activities. Soil tillage and soil impravement operations may loose the soil, while soil wetting due to rainfall, and farming operations as sowing, spraying, weed control and harvesting but also grazing cattle may compact the soil. Compaction may also he caused by land levelling, grading and heavy loading from earthmoving machinery in land consolidation schemes
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
On BCFW shifts of integrands and integrals
In this article a first step is made towards the extension of
Britto-Cachazo-Feng-Witten (BCFW) tree level on-shell recursion relations to
integrands and integrals of scattering amplitudes to arbitrary loop order.
Surprisingly, it is shown that the large BCFW shift limit of the integrands has
the same structure as the corresponding tree level amplitude in any minimally
coupled Yang-Mills theory in four or more dimensions. This implies that these
integrands can be reconstructed from a subset of their `single cuts'. The main
tool is powercounting Feynman graphs in a special lightcone gauge choice
employed earlier at tree level by Arkani-Hamed and Kaplan. The relation between
shifts of integrands and shifts of its integrals is investigated explicitly at
one loop. Two particular sources of discrepancy between the integral and
integrand are identified related to UV and IR divergences. This is
cross-checked with known results for helicity equal amplitudes at one loop. The
nature of the on-shell residue at each of the single-cut singularities of the
integrand is commented upon. Several natural conjectures and opportunities for
further research present themselves.Comment: 43 pages, 6 figures, v2: minor improvement in exposition, typos
fixed, bibliography update
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National audienc
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
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