Strings at the tachyonic vacuum

We study the world-volume effective action of Dp-brane at the tachyonic vacuum which is equivalent to the zero tension limit. Using the Hamiltonian formalism we discuss the algebra of constraints and show that there is a non-trivial ideal of the algebra which corresponds to Virasoro like constraints. The Lagrangian treatment of the model is also considered. For the gauge fixed theory we construct the important subset of classical solutions which is equivalent to the string theory solutions in conformal gauge. We speculate on a possible quantization of the system. At the end a brief discussion of different background fields and fluctuations around the tachyonic vacuum is presented. (author)