Probe branes dynamics in nonconstant background fields

We consider probe p-branes dynamics in string theory backgrounds of general type. We use an action, which interpolates between Nambu-Goto and Polyakov type actions. This allows us to give a unified description for the tensile and tensionless branes. Firstly, we perform our analysis in the frequently used static gauge. Then, we obtain exact brane solutions in more general gauges. The same approach is used to study the Dirichlet p-brane dynamics and here exact solutions are also found. As an illustration, we apply our results to the brane world scenario in the framework of the mirage cosmology approach. (author)