171 research outputs found
Gravity on a fuzzy sphere
We propose an action for gravity on a fuzzy sphere, based on a matrix model.
We find striking similarities with an analogous model of two dimensional
gravity on a noncommutative plane, i.e. the solution space of both models is
spanned by pure U(2) gauge transformations acting on the background solution of
the matrix model, and there exist deformations of the classical diffeomorphisms
which preserve the two-dimensional noncommutative gravity actions.Comment: 14 pages, no figures, LaTe
Hawking radiation for a scalar field conformally coupled to an AdS black hole
The decomposition in normal modes of a scalar field conformally coupled to an
AdS black hole leads to a Heun equation with simple coefficients thanks to
conformal invariance. By applying the Damour-Ruffini method we can relate the
critical exponent of the radial part at the horizon surface to the Hawking
radiation of scalar particles.Comment: 9 pages, no figure
Extended BRS symmetry in topological field theories
A class of topological field theories like the model and Chern-Simons
theory, when quantized in the Landau gauge, enjoys the property of invariance
under a vector supersymmetry, which is responsible for their finiteness. We
introduce a new type of gauge fixing which makes these theories invariant under
an extended symmetry, containing a new type of field, the ghost of
diffeomorphisms. The presence of such an extension is naturally related to the
vector supersymmetry discussed before.Comment: 6 pages, LaTeX, no figure
Non-abelian instantons on a fuzzy four-sphere
We study the compatibility between the instanton and the fuzzy
four-sphere algebra. By using the projective module point of view as an
intermediate step, we are able to identify a non-commutative solution of the
matrix model equations of motion which minimally extends the SU(2) instanton
solution on the classical sphere . We also propose to extend the
non-trivial second Chern class with the five-dimensional noncommutative
Chern-Simons term
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