Edge Singularity for the Optically Induced Kondo Effect in a Quantum Dot

We analyze the optically induced Kondo effect in the absorption spectrum for a quantum dot with an even number of electrons, for which the Kondo effect does not occur in the ground state. The Kondo exchange couplings generated for photo-excited states can be either antiferromagnetic or ferromagnetic, which may result in different types of the edge singularities, depending on the microscopic parameters of the dot. We discuss critical properties in the spectrum by using low-energy effective field theory.