Electron addition spectrum in the supersymmetric t-J model with inverse-square interaction

The electron addition spectrum A(+)(k, omega) is obtained analytically for the one-dimensional (1D) supersymmetric t-J model with 1/r(2) interaction. The result is obtained first for a small-sized system and its validity is c hecked against the numerical calculation. Then the general expression is fo und which is valid for arbitrary size of the system. The thermodynamic limi t of A+(k, omega) has a simple analytic form with contributions from one sp inon, one holon, and one antiholon-all of which obey fractional statistics. The upper edge of A(+)(k, omega) in the (k, omega) plane includes a delta- function peak which reduces to that of the single-electron band in the low- density limit.