D-branes in string theory Melvin backgrounds

We determine the consistent D-brane configurations in type-II nonsupersymmetric Melvin background. The D-branes are analyzed from three complementary points of view: the effective Born-Infeld action, the open-string partition function and the boundary-state approach. We show the agreement of the results obtained by the three different approaches. Among the surprising features is the existence of supersymmetric branes, some of them having a quasiperiodic direction. We also discuss the generalization to backgrounds with several magnetic fields, some of them preserving in the closed and the open spectra some amount of supersymmetry. The case of rational magnetic flux, equivalent to freely-acting noncompact orbifolds, is also studied. It allows more possibilities of consistent D-brane configurations.