283 research outputs found
Perturbative expansion of N<8 Supergravity
We characterise the one-loop amplitudes for N=6 and N=4 supergravity in four
dimensions. For N=6 we find that the one-loop n-point amplitudes can be
expanded in terms of scalar box and triangle functions only. This
simplification is consistent with a loop momentum power count of n-3, which we
would interpret as being n+4 for gravity with a further -7 from the N=6
superalgebra. For N=4 we find that the amplitude is consistent with a loop
momentum power count of n, which we would interpret as being n+4 for gravity
with a further -4 from the N=4 superalgebra. Specifically the N=4 amplitudes
contain non-cut-constructible rational terms.Comment: 13 pages. v2 adds analytic expression for rational parts of 5-pt
1-loop N=4 SUGRA amplitude; v3 normalisations clarifie
Obtaining One-loop Gravity Amplitudes Using Spurious Singularities
The decomposition of a one-loop scattering amplitude into elementary
functions with rational coefficients introduces spurious singularities which
afflict individual coefficients but cancel in the complete amplitude. These
cancellations create a web of interactions between the various terms. We
explore the extent to which entire one-loop amplitudes can be determined from
these relationships starting with a relatively small input of initial
information, typically the coefficients of the scalar integral functions as
these are readily determined. In the context of one-loop gravity amplitudes, of
which relatively little is known, we find that some amplitudes with a small
number of legs can be completely determined from their box coefficients. For
increasing numbers of legs, ambiguities appear which can be determined from the
physical singularity structure of the amplitude. We illustrate this with the
four-point and N=1,4 five-point (super)gravity one-loop amplitudes.Comment: Minor corrections. Appendix adde
The n-point MHV one-loop Amplitude in N=4 Supergravity
We present an explicit formula for the n-point MHV one-loop amplitude in a
N=4 supergravity theory. This formula is derived from the soft and collinear
factorisations of the amplitude.Comment: 8 pages; v2 References added. Minor changes to tex
Supersymmetric Ward Identities and NMHV Amplitudes involving Gluinos
We show how Supersymmetric Ward identities can be used to obtain amplitudes
involving gluinos or adjoint scalars from purely gluonic amplitudes. We obtain
results for all one-loop six-point NMHV amplitudes in \NeqFour Super
Yang-Mills theory which involve two gluinos or two scalar particles. More
general cases are also discussed.Comment: 32 pages, minor typos fixed; one reference adde
Stability of an electroweak string with a fermion condensate
A solution of the standard electroweak theory with a single lepton family is
constructed, consisting of a cosmic string and a fermion condensate within its
core. The stability of this system to small perturbations is examined, and it
is found that stability is not enhanced relative to the bare electroweak
string. The presence of quark zero modes is shown to violate the existence
criteria for embedded defects.Comment: 13 pages, preprint DAMTP 94-9, SWAT/2
Baryon Number Violating Transitions in String Backgrounds
We construct field configurations that interpolate between string background
states of differing baryon number. Using these configurations we estimate the
effect of the background fields on the energy barrier separating different
vacua. In the background of a superconducting GUT string the energy barrier is
increased, while in an electroweak string background or the electroweak layer
of a non-superconducting string the energy barrier is reduced. The energy
barrier depends sensitively on both the background gauge and scalar fields.Comment: 27 pages. Texing problems fixe
Analytic results for two-loop Yang-Mills
Recent Developments in computing very specific helicity amplitudes in two
loop QCD are presented. The techniques focus upon the singular structure of the
amplitude rather than on a diagramatic and integration approachComment: Talk presented at 13th International Symposium on Radiative
Corrections, 24-29 September, 2017,St. Gilgen, Austria, 9 page
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