Different kind of four-dimensional brane for string theory

We present a generalization of the string's Polyakov action that describes a conformally invariant four-dimensional brane. The new extended object is very different from the traditional D-branes of string theory, but, nevertheless, shares some structural similarities with the string, especially when it comes to the low-energy limit of small tension. We introduce a rather rich structure of tensors that can play a role at low energies. In analogy with the bosonic string, we initiate the quantization of the new brane discussing the extent in which it produces a critical dimension of spacetime and Einstein's equations coupled to a scalar dilaton under some approximations.