Variations on Non‐Supersymmetric Strings

We discuss two different themes in non‐supersymmetric strings. First we analyze the backreaction of dilaton tadpoles on the background in a prototype example with 8‐branes. Our analysis of the solutions for the warped metric and the dilaton profile confirms a process of spontaneous compactification in non‐supersymmetric strings. Secondly we consider the construction of non‐supersymmetric closed strings in various dimensions using orbifolds. We partially classify tachyon‐free heterotic models and compute the spectrum of several tachyonic type II and heterotic examples. We also discuss the relation to compactification on K3 and Calabi‐Yau manifolds.