X-ray edge singularity in integrable lattice models of correlated electrons

We study the singularities in x-ray absorption spectra of one-dimensional Hubbard and t-J models. We use boundary conformal field theory and the Bethe ansatz solutions of these models with both periodic and open boundary conditions to calculate the exponents describing the power-law decay near the edges of x-ray absorption spectra in the case where the core-hole potential has bound states