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In this note the open string partition function is analyzed carefully in a way to reveal the group-theoretical aspects. For the simple cases of ADE orbifolds with regular Chan-Paton action a prescription for consistent boundary states is given. In the process of outlining how they encode McKay correspondence, we argue that this results from a non-trivial conspiracy of numerical factors in the string amplitudes., Comment: Latex, 11 pages, no figures

Closed type 0 string theories and their D-branes are introduced. The full Wess-Zumino action of these D-branes is derived. The analogy with type II is emphasized throughout the argument., Comment: 4 pages, latex, uses cargese.cls, contribution to proceedings of NATO-ASI and TMR Summer School "Progress in String Theory and M-theory", Cargese, May 24 - June 5 1999 (talk by Ben Craps)

Non-BPS type II D-branes couple to R-R potentials via an action that, upon tachyon condensation, gives rise to the Wess-Zumino action of BPS D-branes., Comment: 4 pages, latex, uses cargese.cls, contribution to proceedings of NATO-ASI and TMR Summer School "Progress in String Theory and M-theory", Cargese, May 24 - June 5 1999 (talk by Frederik Roose)

The massless degrees of freedom of type 0 NS5-branes are derived. A non-chiral, purely bosonic spectrum is found in both type 0A and 0B. This non-chirality is confirmed by a one-loop computation in the bulk. Some puzzles concerning type 0B S-duality are pointed out in this context. An interpretation of the spectra in terms of ``type 0 little strings'' is proposed., Comment: LaTeX, 12 pages, no figures; v3: section on S-duality revised, references added, to be published in JHEP

We study how non-BPS type II D-branes couple to R-R potentials. Upon tachyon condensation the couplings we find give rise to the Wess-Zumino action of BPS D-branes., Comment: LaTeX, 8 pages, no figures; minor changes, reference added, to be published in JHEP

Using boundary states we derive the presence of (chiral) fermions on the intersection of type 0 D-branes. The corresponding anomalous couplings on the branes are then computed. Furthermore, we discuss systems of branes sitting at $A_n$ singularities. In particular, the massless spectrum on the branes is derived, and a boundary state description is given., Comment: 13 pages, LaTeX2e, 1 figure; v2: presentation made more self-contained, version to be published in Phys. Lett. B

The direct string computation of anomalous D-brane and orientifold plane couplings is extended to include the curvature of the normal bundle. The normalization of these terms is fixed unambiguously. New, non-anomalous gravitational couplings are found., Comment: 6 pages, latex, no figures; version accepted for publication in Phys. Lett. B

We compute scattering amplitudes involving both R-R and NS-NS fields in the presence of a D-brane or orientifold plane. These provide direct evidence for the anomalous couplings in the D-brane and orientifold actions. The D9-brane and O9-plane are found to couple to the first Pontrjagin class with the expected relative strength., Comment: 13 pages, latex, no figures, proposal to fix factor of 2 added, minor corrections, reference added, version to be published in Phys. Lett. B

The scalars in vector multiplets of N=2 supersymmetric theories in 4 dimensions exhibit `special Kaehler geometry', related to duality symmetries, due to their coupling to the vectors. In the literature there is some confusion on the definition of special geometry, which we want to clear up, for rigid as well as for local N=2., Comment: 6 pages Latex using sprocl.sty, no figures