We discuss direct production of Regge excitations in the collisions of
massless four-dimensional superstring states, focusing on the first excited
level of open strings ending on D-branes extending into higher dimensions. We
construct covariant vertex operators and identify ``universal'' Regge states
with the internal parts either trivial or determined by the world-sheet SCFT
describing superstrings propagating on an arbitrary Calabi-Yau manifold. We
evaluate the amplitudes involving one such massive state and up to three
massless ones and express them in the helicity basis. The most important
phenomenological applications of our results are in the context of low-mass
string (and large extra dimensions) scenarios in which excited string states
are expected to be produced at the LHC as soon as the string mass threshold is
reached in the center-of-mass energies of the colliding partons. In order to
facilitate the use of partonic cross sections, we evaluate them and tabulate
for all production processes: gluon fusion, quark absorbing a gluon,
quark-antiquark annihilation and quark-quark scattering.Comment: 43 pages, RevTeX 4.
