1,435 research outputs found
Next-to-Maximal Helicity Violating Amplitudes in Gauge Theory
Using the novel diagrammatic rules recently proposed by Cachazo, Svrcek, and
Witten, I give a compact, manifestly Lorentz-invariant form for tree-level
gauge-theory amplitudes with three opposite helicities.Comment: 12 pages, 1 figur
Two-Loop Four-Gluon Amplitudes in N=4 Super-Yang-Mills
Using cutting techniques we obtain the two-loop N=4 super-Yang-Mills helicity
amplitudes for four-gluon scattering in terms of scalar integral functions. The
N=4 amplitudes are considerably simpler than corresponding QCD amplitudes and
therefore provide a testing ground for exploring two-loop amplitudes. The
amplitudes are constructed directly in terms of gauge invariant quantities and
therefore remain relatively compact throughout the calculation. We also present
a conjecture for the leading color four-gluon amplitudes to all orders in the
perturbative expansion.Comment: Latex, 13 pages, 9 figures, minor changes to signs in eq.(14
Twistor Space Structure of the Box Coefficients of N=1 One-loop Amplitudes
We examine the coefficients of the box functions in N=1 supersymmetric
one-loop amplitudes. We present the box coefficients for all six point N=1
amplitudes and certain all example coefficients. We find for ``next-to
MHV'' amplitudes that these box coefficients have coplanar support in twistor
space.Comment: 14 pages, minor typos correcte
All Non-Maximally-Helicity-Violating One-Loop Seven-Gluon Amplitudes in N=4 Super-Yang-Mills Theory
We compute the non-MHV one-loop seven-gluon amplitudes in N=4
super-Yang-Mills theory, which contain three negative-helicity gluons and four
positive-helicity gluons. There are four independent color-ordered amplitudes,
(- - - + + + +), (- - + - + + +), (- - + + -+ +) and (- + - + - + +). The MHV
amplitudes containing two negative-helicity and five positive-helicity gluons
were computed previously, so all independent one-loop seven-gluon helicity
amplitudes are now known for this theory. We present partial information about
an infinite sequence of next-to-MHV one-loop helicity amplitudes, with three
negative-helicity and n-3 positive-helicity gluons, and the color ordering (- -
- + + ... + +); we give a new coefficient of one class of integral functions
entering this amplitude. We discuss the twistor-space properties of the
box-integral-function coefficients in the amplitudes, which are quite simple
and suggestive.Comment: 54 pages, v3 minor correction
Perturbative Relations between Gravity and Gauge Theory
We review the relations that have been found between multi-loop scattering
amplitudes in gauge theory and gravity, and their implications for ultraviolet
divergences in supergravity.Comment: LaTex with package axodraw.sty. 10 pages. Presented by L.D. at
Strings 99. Cosmetic changes onl
Loops in Twistor Space
We elucidate the one-loop twistor-space structure corresponding to
momentum-space MHV diagrams. We also discuss the infrared divergences, and
argue that only a limited set of MHV diagrams contain them. We show how to
introduce a twistor-space regulator corresponding to dimensional regularization
for the infrared-divergent diagrams. We also evaluate explicitly the
`holomorphic anomaly' pointed out by Cachazo, Svrcek, and Witten, and use the
result to define modified differential operators which can be used to probe the
twistor-space structure of one-loop amplitudes.Comment: 21 pages, TeX. v3. missing citations added. v4. subtlety with the i
\epsilon prescription clarifie
A technique for loop calculations in non-Abelian gauge theories - with application to five gluon amplitude
A powerful tool for calculations in non-Abelian gauge theories is obtained by
combining the background field gauge, the helicity basis and the color
decomposition methods. It has reproduced the one-loop calculation of the
five-gluon amplitudes in QCD, is applicable to electroweak processes and
extendable to two-loop calculations.Comment: Latex 22 pages, 3 figure
One-Loop NMHV Amplitudes involving Gluinos and Scalars in N=4 Gauge Theory
We use Supersymmetric Ward Identities and quadruple cuts to generate n-pt
NMHV amplitudes involving gluinos and adjoint scalars from purely gluonic
amplitudes. We present a set of factors that can be used to generate one-loop
NMHV amplitudes involving gluinos or adjoint scalars in N=4 Super Yang-Mills
from the corresponding purely gluonic amplitude.Comment: 16 pages, JHEP versio
Fluorescence Correlation Spectroscopy analysis of segmental dynamics in Actin filaments
We adapt Fluorescence Correlation spectroscopy (FCS) formalism to the studies
of the dynamics of semi-flexible polymers and derive expressions relating FCS
correlation function to the longitudinal and transverse mean square
displacements of polymer segments. We use the derived expressions to measure
the dynamics of actin filaments in two experimental situations: filaments
labeled at distinct positions and homogeneously labeled filaments. Both
approaches give consistent results and allow to measure the temporal dependence
of the segmental mean-square displacement (MSD) over almost five decades in
time, from ~0.04ms to 2s. These noninvasive measurements allow for a detailed
quantitative comparison of the experimental data to the current theories of
semi-flexible polymer dynamics. Good quantitative agreement is found between
the experimental results and theories explicitly accounting for the
hydrodynamic interactions between polymer segments
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