8,029 research outputs found
Spacetime Emergence and General Covariance Transmutation
Spacetime emergence refers to the notion that classical spacetime "emerges"
as an approximate macroscopic entity from a non-spatio-temporal structure
present in a more complete theory of interacting fundamental constituents. In
this article, we propose a novel mechanism involving the "soldering" of
internal and external spaces for the emergence of spacetime and the twin
transmutation of general covariance. In the context of string theory, this
mechanism points to a critical four dimensional spacetime background.Comment: 11 pages, v2: version to appear in MPL
General covariance, and supersymmetry without supersymmetry
An unusual four-dimensional generally covariant and supersymmetric SU(2)
gauge theory is described. The theory has propagating degrees of freedom, and
is invariant under a local (left-handed) chiral supersymmetry, which is half
the supersymmetry of supergravity. The Hamiltonian 3+1 decomposition of the
theory reveals the remarkable feature that the local supersymmetry is a
consequence of Yang-Mills symmetry, in a manner reminiscent of how general
coordinate invariance in Chern-Simons theory is a consequence of Yang-Mills
symmetry. It is possible to write down an infinite number of conserved
currents, which strongly suggests that the theory is classically integrable. A
possible scheme for non-perturbative quantization is outlined. This utilizes
ideas that have been developed and applied recently to the problem of
quantizing gravity.Comment: 17 pages, RevTeX, two minor errors correcte
Quantum Determinism from Quantum General Covariance
The requirement of general covariance of quantum field theory (QFT) naturally
leads to quantization based on the manifestly covariant De Donder-Weyl
formalism. To recover the standard noncovariant formalism without violating
covariance, fields need to depend on time in a specific deterministic manner.
This deterministic evolution of quantum fields is recognized as a covariant
version of the Bohmian hidden-variable interpretation of QFT.Comment: 6 pages, revised, new references, Honorable Mention of the Gravity
Research Foundation 2006 Essay Competition, version to appear in Int. J. Mod.
Phys.
Extending general covariance: Moyal-type noncommutative manifolds
In the Hamiltonian formulation of general relativity, Einstein's equation is
replaced by a set of four constraints. Classically, the constraints can be
identified with the generators of the hypersurface-deformation Lie algebroid
(HDA) that belongs to the groupoid of finite evolutions in space-time. Taken
over to deformed general relativity, this connection allows one to study
possible Drinfeld twists of space-time diffeomorphisms with Hopf-algebra
techniques. After a review of noncommutative differential structures, two cases
--- twisted diffeomorphisms with standard action and deformed (or -)
diffeomorphisms with deformed action --- are considered in this paper. The HDA
of twisted diffeomorphisms agrees with the classical one, while the HDA
obtained from deformed diffeomorphisms is modified due to the explicit presence
of -products in the brackets. The results allow one to distinguish
between twisted and deformed symmetries, and they indicate that the latter
should be regarded as the relevant symmetry transformations for noncommutative
manifolds. The algebroid brackets maintain the same general structure
regardless of space-time noncommutativity, but they still show important
consequences of non-locality
Two dimensional general covariance from three dimensions
A 3d generally covariant field theory having some unusual properties is
described. The theory has a degenerate 3-metric which effectively makes it a 2d
field theory in disguise. For 2-manifolds without boundary, it has an infinite
number of conserved charges that are associated with graphs in two dimensions
and the Poisson algebra of the charges is closed. For 2-manifolds with boundary
there are additional observables that have a Kac-Moody Poisson algebra. It is
further shown that the theory is classically integrable and the general
solution of the equations of motion is given. The quantum theory is described
using Dirac quantization, and it is shown that there are quantum states
associated with graphs in two dimensions.Comment: 10 pages (Latex), Alberta-Thy-19-9
General Covariance in Algebraic Quantum Field Theory
In this review we report on how the problem of general covariance is treated
within the algebraic approach to quantum field theory by use of concepts from
category theory. Some new results on net cohomology and superselection
structure attained in this framework are included.Comment: 61 pages, 3 figures, LaTe
General covariance of the non-abelian DBI-action
In this paper we study the action for N D0-branes in a curved background. In
particular, we focus on the meaning of space-time diffeomorphism invariance.
For a single D-brane, diffeomorphism invariance acts in a naive way on the
world-volume fields, but for multiple D-branes, the meaning of diffeomorphism
invariance is much more obscure. The problem goes beyond the determination of
an ordering of the U(N)-valued fields, because one can show that there is no
lift of ordinary diffeomorphisms to matrix-valued diffeomorphisms. On the other
hand, the action can presumably be constructed from perturbative string theory
calculations. Based on the general characteristics of such calculations we
determine a set of constraints on the action for N D0-branes, that ensure
space-time covariance. These constraints can be solved order by order, but they
are insufficient to determine the action completely. All solutions to the
constraints obey the axioms of D-geometry. Moreover the action must contain new
terms. This exhibits clearly that the answer is more than a suitable ordering
of the action of a single D0 brane.Comment: latex, 38 page
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