12,125 research outputs found
Recurrent Acceleration in Dilaton-Axion Cosmology
A class of Einstein-dilaton-axion models is found for which almost all flat
expanding homogeneous and isotropic universes undergo recurrent periods of
acceleration. We also extend recent results on eternally accelerating open
universes.Comment: 8 pages, 7 figures. minor changes. Version 4 corrects a figure
captio
Surprises with angular momentum
The physics of angular momentum in even space dimensions can be surprisingly
counter-intuitive. Three such suprises, all associated with the properties of
supersymmetric rotating objects, are examined: (i) 5D black holes, (ii) Dyonic
instantons and (iii) Supertubes.Comment: 11 pp. Contribution to proceedings of TH-2002; revised to include
typographical corrections and further reference
p-Brane Democracy
The ten or eleven dimensional origin of central charges in the N=4 or N=8
supersymmetry algebra in four dimensions is reviewed: while some have a
standard Kaluza-Klein interpretation as momenta in compact dimensions, most
arise from -form charges in the higher-dimensional supersymmetry algebra
that are carried by -brane `solitons'. Although is singled out by
superstring perturbation theory, U-duality of N=8 superstring compactifications
implies a complete `-brane democracy' of the full non-perturbative theory.
An `optimally democratic' perturbation theory is defined to be one in which the
perturbative spectrum includes all particles with zero magnetic charge. Whereas
the heterotic string is optimally democratic in this sense, the type II
superstrings are not, although the 11-dimensional supermembrane might be.Comment: Some typos, and typographical problems, of previous revised version
corrected. 15 pp. Latex. This paper will appear in the proceedings of the
March 95 PASCOS/Johns Hopkins conferenc
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