The Fermi edge singularity and boundary condition changing operators

Abstract
The boundary conformal field theory approach to quantum impurity problems is used to study the Fermi edge singularity, occurring in the X-ray adsorption probability. The deep-hole creation operator, in the effective low-energy theory, changes the boundary condition on the conduction electrons. By a conformal mapping, the dimension of such an operator is related to the ground-state energy for a finite system with different boundary conditions at the two ends. The Fermi edge singularity is solved, using this method, for the Luttinger liquid including backscattering and for the multi-channel Kondo problem.
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