A conformally invariant generalization of string theory to   higher-dimensional objects. Hierarchy of coupling constants
  We suggest a conformally invariant generalization of string theory to higher-dimensional objects. As such a model, we consider a conformally invariant $\sigma$ model. For this theory, the Hamiltonian formalism is constructed, and the full set of constraints is found. The equations obtained are studied under a fixed gauge. It is shown that special cases of the model are string theory and Einstein's theory of gravity. Cosmological application of the suggested theory are studied. It is shown that Friedmann-like models can be described in this framework. Our models make it possible to interpret the Universe evolution as evolution of three-dimensional objects embedded in a higher-dimensional flat space-time. 
F. Zaripov