Interference and interaction effects in multilevel quantum dots

Using renormalization group techniques, we study spectral and transport properties of a spinless interacting quantum dot consisting of two levels coupled to metallic reservoirs. For strong Coulomb repulsion U and an applied Aharonov-Bohm phase $\phi ,$ we find a large direct tunnel splitting $|\Delta |\sim (\Gamma /\pi )|\cos (\phi /2)|\ln (U/{\omega }_c)$ between the levels of the order of the level broadening $\Gamma .$ As a consequence we discover a many-body resonance in the spectral density that can be measured via the absorption power. Furthermore, for $\phi =\pi ,$ we show that the system can be tuned into an effective Anderson model with spin-dependent tunneling.