Immersions and folds in string theories of gauge fields

A two-dimensional string model with dynamical cancellation of folds is considered. The action of the model contains the self-intersection number which is defined for surfaces immersed into 4D targets. The two additional variables are not dynamical and live on a compact manifold. In this sense the model is a compactification of a 4D theory. The cancellation forces the string $\th$ angle to be equal $\pi$. Candidates for string states are constructed. Some mathematical background is given.Comment: 22 pages, 3 Postscript figures, accepted for publication in Int.J.Mod.Phys.

Matrix description of D-branes on 3-spheres

We discuss a matrix model for D0-branes on S^3 \times M^7 based on quantum group symmetries. For finite radius of S^3 (i.e. for finite k), it gives results beyond the reach of the ordinary matrix model. For large k all known static properties of branes on S^3 are reproduced.Comment: 14 pages, LaTe

AdS_5 x S^5 Black Hole Metric at O(alpha'^3)

We compute $O(\alpha'^3)$ corrections to the $AdS_5\times S^5$ black hole metric. We find that the radius of the $S^5$ depends on the radial $AdS_5$ coordinate. This completes the computation of Gubser, Klebanov and Tseytlin (hep-th/9805156). The fact that the metric no longer factorizes should modify the value of the Wilson line at finite temperature and the glueball mass spectrum.Comment: 7 pages, TeX (harvmac