41,578 research outputs found
Lsdiff M and the Einstein Equations
We give a formulation of the vacuum Einstein equations in terms of a set of
volume-preserving vector fields on a four-manifold . These vectors
satisfy a set of equations which are a generalisation of the Yang-Mills
equations for a constant connection on flat spacetime.Comment: 5 pages, no figures, Latex, uses amsfonts, amssym.def and amssym.tex.
Note added on more direct connection with Yang-Mills equation
The ADHM construction and non-local symmetries of the self-dual Yang-Mills equations
We consider the action on instanton moduli spaces of the non-local symmetries
of the self-dual Yang-Mills equations on discovered by Chau and
coauthors. Beginning with the ADHM construction, we show that a sub-algebra of
the symmetry algebra generates the tangent space to the instanton moduli space
at each point. We explicitly find the subgroup of the symmetry group that
preserves the one-instanton moduli space. This action simply corresponds to a
scaling of the moduli space.Comment: AMSLatex, 19 pages, no figures. Some discussions clarified, and
citations made more accurate. I am grateful to the referee for detailed
comments. Version to appear in Communications in Mathematical Physic
A Spinorial Hamiltonian Approach to Gravity
We give a spinorial set of Hamiltonian variables for General Relativity in
any dimension greater than 2. This approach involves a study of the algebraic
properties of spinors in higher dimension, and of the elimination of
second-class constraints from the Hamiltonian theory. In four dimensions, when
restricted to the positive spin-bundle, these variables reduce to the standard
Ashtekar variables. In higher dimensions, the theory can either be reduced to a
spinorial version of the ADM formalism, or can be left in a more general form
which seems useful for the investigation of some spinorial problems such as
Riemannian manifolds with reduced holonomy group. In dimensions ,
the theory may be recast solely in terms of structures on the positive
spin-bundle , but such a reduction does not seem possible in
dimensions , due to algebraic properties of spinors in these
dimensions.Comment: 20 pages, Latex 2e. Published versio
Cosmic Strings and Chronology Protection
A space consisting of two rapidly moving cosmic strings has recently been
constructed by Gott that contains closed timelike curves. The global structure
of this space is analysed and is found that, away from the strings, the space
is identical to a generalised Misner space. The vacuum expectation value of the
energy momentum tensor for a conformally coupled scalar field is calculated on
this generalised Misner space. It is found to diverge very weakly on the
Chronology horizon, but more strongly on the polarised hypersurfaces. The
divergence on the polarised hypersurfaces is strong enough that when the proper
geodesic interval around any polarised hypersurface is of order the Planck
length squared, the perturbation to the metric caused by the backreaction will
be of order one. Thus we expect the structure of the space will be radically
altered by the backreaction before quantum gravitational effects become
important. This suggests that Hawking's `Chronology Protection Conjecture'
holds for spaces with non-compactly generated Chronology horizon.Comment: 15 pages, plain TeX, 2 figures (not included), DAMTP-R92/3
The WTO and the Cartagena Protocol: International Policy Coordination or Conflict?
International policy coordination is a challenging exercise requiring policy rapprochement among sovereign nations that often have very different political economy situations. Successful efforts may even result in the creation of multilateral paradigms such as trade agreements or multilateral environmental agreements (MEAs). Typically, there is overlap between these independent paradigms; sometimes in the nexus there is policy coordination and other times there is conflict. An understanding of the factors that account for coordination and conflict is crucial in ensuring that any benefits from policy coordination that may be achieved in one paradigm are not eroded through conflicts with another paradigm. This article presents a case study of the implications of overlapping multilateral paradigms â the World Trade Organization and an MEA known as the Cartagena Protocol on Biosafety â for international market access of biotechnology-based agri-food products.Agricultural and Food Policy, International Relations/Trade,
Increasing the Openness of the Trade Policy Process: Challenges and Implications
Trade policy Ăâ once a subset of foreign policy far removed from domestic concern, focused squarely on border issues and subject to the rules of international diplomacy Ăâ is now a central concern on the public policy agenda as trade issues have become increasingly entwined with traditionally domestic policy issues. Consequently, demands have been made for more openness in trade policy formation and, in response, many governments have undertaken openness initiatives. Despite these developments there has been only a little research into the increased openness of trade policy processes in general and no research aimed at developing a consistent framework for categorizing various openness initiatives and permitting a meaningful comparison of initiatives between trading partners. In this paper, the general issue of increasing the openness of trade policy is examined, an openness framework is proposed and the implications for trade policy are assessed.openness, openness framework, trade policy, transparency, International Relations/Trade,
- âŠ