Quantum dynamics of relativistic massive strings

The string is defined here as a relativistic generalization of the classical massive inhomogeneous string. A covariant Hamiltonian method is used for quantization. It is shown that the orthonormal parametrization constraint can be used only when the string is homogeneous, while a special transverse gauge type of covariant constraint can be used always and it gives $a_n^0|m,\overrightarrow{\mathrm{p}}=0,s〉=0\mathrm{}$ in the rest frame of reference. This condition ensures the positivity of norms of states with $m^2>0\mathrm{}$ and $p^0>0\mathrm{}$. The origins of difficulties with present relativistic quantum theories of the string are pointed out and also resolved. In addition, we study quantum electrodynamics of the string.