15,761 research outputs found
T-Duality and Non-Local Realizations of Supersymmetry in String Theory
We study non-local realizations of extended worldsheet supersymmetries and
the associated space-time supersymmetries which arise under a T-duality
transformation. These non-local effects appear when the supersymmetries do not
commute with the isometry with respect to which T-duality is performed.Comment: 6 pages, Latex, Talk presented at the Workshop on Strings, Gravity
and Related Topics, Trieste, 29-30 June 199
Particular Solutions in Bimetric Theory and Their Implications
Ghost-free bimetric theory can describe gravity in the presence of an extra
spin-2 field. We study certain aspects of dynamics in this theory: (1) It is
shown that if either of the metrics is an Einstein solution then the other is
always forced to be Einstein, too. For a class of bimetric models this
constraint is stronger and as soon as one metric is Einstein, the other metric
is forced to be proportional to it. As a consequence, the models in this class
avoid a branch of pathological solutions that exhibit determinant singularities
or nonlinear ghosts. These constraints persists in a generalized form when
sources are included, but are destroyed in the massive gravity limit of the
theory. (2) For another class of bimetric models, we show the existence of
solutions that do not admit a massive gravity limit. A bimetric model that
could exhibit a nonlinear version of "partially massless" symmetry belongs to
both these classes. It is argued that if such a model exits, its symmetry will
not survive in the massive gravity limit.Comment: Latex, 18 pages. Published versio
Extended Weyl Invariance in a Bimetric Model and Partial Masslessness
We revisit a particular ghost-free bimetric model which is related to both
partial masslessness (PM) and conformal gravity. Linearly, the model propagates
six instead of seven degrees of freedom not only around de Sitter but also
around flat spacetime. Nonlinearly, the equations of motion can be recast in
the form of expansions in powers of curvatures, and exhibit a remarkable amount
of structure. In this form, the equations are shown to be invariant under
scalar gauge transformations, at least up to six orders in derivatives, the
lowest order term being a Weyl scaling of the metrics. The terms at
two-derivative order reproduce the usual PM gauge transformations on de Sitter
backgrounds. At the four-derivative order, a potential obstruction that could
destroy the symmetry is shown to vanish. This in turn guarantees the gauge
invariance to at least six-orders in derivatives. This is equivalent to adding
up to 10-derivative corrections to conformal gravity. More generally, we
outline a procedure for constructing the gauge transformations order by order
as an expansion in derivatives and comment on the validity and limitations of
the procedure. We also discuss recent arguments against the existence of a PM
gauge symmetry in bimetric theory and show that, at least in their present
form, they are evaded by the model considered here. Finally, we argue that a
bimetric approach to PM theory is more promising than one based on the
existence of a fundamental PM field.Comment: Latex, 35 pages. Matches published versio
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