11 research outputs found
On amplitudes in self-dual sector of Yang-Mills theory
Self-dual perturbiner in the Yang-Mills theory is constructed by the twistor
methods both in topologically trivial and topologically nontrivial cases.
Maximally helicity violating amplitudes and their instanton induced analogies
are briefly discussed.Comment: 9 pages, Latex, a misguided reference is corrected, ps is also
available at http://wwwtheor.itep.ru/preprints/1996
From Yang-Mills Lagrangian to MHV Diagrams
We prove the equivalence of a recently suggested MHV-formalism to the
standard Yang-Mills theory. This is achieved by a formally non-local change of
variables. In this note we present the explicit formulas while the detailed
proofs are postponed to a future publication.Comment: Latex,11 pages, minor changes, reference added, version to appear in
JHE
On Five-dimensional Superspaces
Recent one-loop calculations of certain supergravity-mediated quantum
corrections in supersymmetric brane-world models employ either the component
formulation (hep-th/0305184) or the superfield formalism with only half of the
bulk supersymmetry manifestly realized (hep-th/0305169 and hep-th/0411216).
There are reasons to expect, however, that 5D supergraphs provide a more
efficient setup to deal with these and more involved (in particular,
higher-loop) calculations. As a first step toward elaborating such supergraph
techniques, we develop in this letter a manifestly supersymmetric formulation
for 5D globally supersymmetric theories with eight supercharges. Simple rules
are given to reduce 5D superspace actions to a hybrid form which keeps manifest
only the 4D, N=1 Poincare supersymmetry. (Previously, such hybrid actions were
carefully worked out by rewriting the component actions in terms of simple
superfields). To demonstrate the power of this formalism for model building
applications, two families of off-shell supersymmetric nonlinear sigma-models
in five dimensions are presented (including those with cotangent bundles of
Kahler manifolds as target spaces). We elaborate, trying to make our
presentation maximally clear and self-contained, on the techniques of 5D
harmonic and projective superspaces used at some stages in this letter.Comment: 46 pages, 3 figures. V5: version published in JHE
On Superspace Chern-Simons-like Terms
We search for superspace Chern-Simons-like higher-derivative terms in the low
energy effective actions of supersymmetric theories in four dimensions.
Superspace Chern-Simons-like terms are those gauge-invariant terms which cannot
be written solely in terms of field strength superfields and covariant
derivatives, but in which a gauge potential superfield appears explicitly. We
find one class of such four-derivative terms with N=2 supersymmetry which,
though locally on the Coulomb branch can be written solely in terms of field
strengths, globally cannot be. These terms are classified by certain Dolbeault
cohomology classes on the moduli space. We include a discussion of other
examples of terms in the effective action involving global obstructions on the
Coulomb branch.Comment: 23 pages; a reference and an author email correcte
Higher-Derivative Terms in N=2 Supersymmetric Effective Actions
We show how to systematically construct higher-derivative terms in effective
actions in harmonic superspace despite the infinite redundancy in their
description due to the infinite number of auxiliary fields. Making an
assumption about the absence of certain superspace Chern-Simons-like terms
involving vector multiplets, we write all 3- and 4-derivative terms on Higgs,
Coulomb, and mixed branches. Among these terms are several with only
holomorphic dependence on fields, and at least one satisfies a
non-renormalization theorem. These holomorphic terms include a novel
3-derivative term on mixed branches given as an integral over 3/4 of
superspace. As an illustration of our method, we search for Wess-Zumino terms
in the low energy effective action of N=2 supersymmetric QCD. We show that such
terms occur only on mixed branches. We also present an argument showing that
the combination of space-time locality with supersymmetry implies locality in
the anticommuting superspace coordinates of for unconstrained superfields.Comment: 30 pages. Added references and simplified final form of WZ ter
Anomalous Magnetic Properties of Sr2YRuO6
Anomalous magnetic properties of the double perovskite ruthenates compound
Sr2YRuO6 are reported here. Magnetization measurements as a function of
temperature in low magnetic fields show clear evidence for two components of
magnetic order (TM1 ~ 32K and TM2 ~ 27K) aligned opposite to each other with
respect to the magnetic field direction even though only Ru5+moments can order
magnetically in this compound. The second component of the magnetic order at
TM2 ~ 27K results only in a magnetization reversal, and not in the negative
magnetization when the magnetization is measured in the field cooled (FC) mode.
Isothermal magnetization (M-H) measurements show hysteresis with maximum
coercivity (Hc) and remnant magnetization (Mr) at T ~ 27 K, corroborating the
presence of the two oppositely aligned magnetic moments, each with a
ferromagnetic component. The two components of magnetic ordering are further
confirmed by the double peak structure in the heat capacity measurements. These
anomalous properties have significance to some of the earlier results obtained
for the Cu-substituted superconducting Sr2YRu1-xCuxO6 compounds.Comment: 6 figur
Gravity, Twistors and the MHV Formalism
We give a self-contained derivation of the MHV amplitudes for gravity and use
the associated twistor generating function to define a twistor action for the
MHV diagram approach to gravity. Starting from a background field calculation
on a spacetime with anti self-dual curvature, we obtain a simple spacetime
formula for the scattering of a single, positive helicity linearized graviton
into one of negative helicity. Re-expressing our integral in terms of twistor
data allows us to consider a spacetime that is asymptotic to a superposition of
plane waves. Expanding these out perturbatively yields the gravitational MHV
amplitudes of Berends, Giele & Kuijf. We go on to take the twistor generating
function off-shell at the perturbative level. Combining this with a twistor
action for the anti self-dual background, we obtain a twistor action for the
MHV diagram approach to perturbative gravity. We finish by extending these
results to supergravity, in particular N=4 and N=8.Comment: 39 pages, 3 figures. Minor typos corrected, some clarification adde