27,921 research outputs found
Higher Spin BRS Cohomology of Supersymmetric Chiral Matter in D=4
We examine the BRS cohomology of chiral matter in , supersymmetry
to determine a general form of composite superfield operators which can suffer
from supersymmetry anomalies. Composite superfield operators \Y_{(a,b)} are
products of the elementary chiral superfields and \ov S and the
derivative operators D_\a, \ov D_{\dot \b} and \pa_{\a \dot \b}. Such
superfields \Y_{(a,b)} can be chosen to have `' symmetrized undotted
indices \a_i and `' symmetrized dotted indices \dot \b_j. The result
derived here is that each composite superfield \Y_{(a,b)} is subject to
potential supersymmetry anomalies if is an odd number, which means that
\Y_{(a,b)} is a fermionic superfield.Comment: 15 pages, CPT-TAMU-20/9
All-Orders Singular Emission in Gauge Theories
I present a class of functions unifying all singular limits for the emission
of soft or collinear gluons in gauge-theory amplitudes at any order in
perturbation theory. Each function is a generalization of the antenna functions
of ref. [1]. The helicity-summed interferences these functions are thereby also
generalizations to higher orders of the Catani--Seymour dipole factorization
function.Comment: 5 pages, 1 figur
On-Shell Methods in Perturbative QCD
We review on-shell methods for computing multi-parton scattering amplitudes
in perturbative QCD, utilizing their unitarity and factorization properties. We
focus on aspects which are useful for the construction of one-loop amplitudes
needed for phenomenological studies at the Large Hadron Collider.Comment: 49 pages, 15 figures. v2: minor typos correcte
The Last of the Finite Loop Amplitudes in QCD
We use on-shell recursion relations to determine the one-loop QCD scattering
amplitudes with a massless external quark pair and an arbitrary number (n-2) of
positive-helicity gluons. These amplitudes are the last of the unknown
infrared- and ultraviolet-finite loop amplitudes of QCD. The recursion
relations are similar to ones applied at tree level, but contain new
non-trivial features corresponding to poles present for complex momentum
arguments but absent for real momenta. We present the relations and the compact
solutions to them, valid for all n. We also present compact forms for the
previously-computed one-loop n-gluon amplitudes with a single negative helicity
and the rest positive helicity.Comment: 45 pages, revtex, 7 figures, v2 minor correction
Classical String in Curved Backgrounds
The Mathisson-Papapetrou method is originally used for derivation of the
particle world line equation from the covariant conservation of its
stress-energy tensor. We generalize this method to extended objects, such as a
string. Without specifying the type of matter the string is made of, we obtain
both the equations of motion and boundary conditions of the string. The world
sheet equations turn out to be more general than the familiar minimal surface
equations. In particular, they depend on the internal structure of the string.
The relevant cases are classified by examining canonical forms of the effective
2-dimensional stress-energy tensor. The case of homogeneously distributed
matter with the tension that equals its mass density is shown to define the
familiar Nambu-Goto dynamics. The other three cases include physically relevant
massive and massless strings, and unphysical tahyonic strings.Comment: 12 pages, REVTeX 4. Added a note and one referenc
BRS Cohomology of the Supertranslations in D=4
Supersymmetry transformations are a kind of square root of spacetime
translations. The corresponding Lie superalgebra always contains the
supertranslation operator . We find that the
cohomology of this operator depends on a spin-orbit coupling in an SU(2) group
and has a quite complicated structure. This spin-orbit type coupling will turn
out to be basic in the cohomology of supersymmetric field theories in general.Comment: 14 pages, CTP-TAMU-13/9
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