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 $p$-form charges in the higher-dimensional supersymmetry algebra that are carried by $p$-brane `solitons'. Although $p=1$ is singled out by superstring perturbation theory, U-duality of N=8 superstring compactifications implies a complete `$p$-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

The Manifestly Sl(2;Z)-covariant Superstring

We present a manifestly Sl(2;Z)-covariant action for the type IIB superstring, and prove kappa-symmetry for on-shell IIB supergravity backgrounds.Comment: 13 pages, plain tex. Two minor corrections. Reference adde

Super D-branes

We present a manifestly Lorentz invariant, spacetime supersymmetric, and `$\kappa$-invariant' worldvolume action for all type II Dirichlet p-branes, $p\le9$, in a general type II supergravity background, including massive backgrounds in the IIA case. The $p=0,2$ cases are rederived from D=11. The $p=9$ case provides a supersymmetrization of the D=10 Born-Infeld action.Comment: 27pp. Typos corrected. To appear in Nucl. Phys.

Solitons on the Supermembrane

Energy bounds are derived for planar and compactified M2-branes in a hyper-K\"ahler background. These bounds are saturated, respectively, by lump and Q-kink solitons, which are shown to preserve a half of the worldvolume supersymmetry. The Q-kinks have a dual IIB interpretation as strings that migrate between fivebranes.Comment: 18 pp. Latex; v2: minor corrections, version as published in JHE