Neutron matter and pairing in finite nuclei

We calculate the energy per particle and pressure in neutron matter based on chirl nucleon-nucleon (NN) and three-nucleon (3N) interactions. For this we derive an effective density- dependent NN interaction from the leading order (NNLO) 3N interaction by averaging one particle over the Fermi sea. This effective forec can be incorporated in a straightforward way in existing many-body calculations. Furthermore we investigate pairing gaps based upon microoscopic NN interactions in finite nuclei in the framework of the density-functional theory. We find that pairing gaps obtained from low-momentum interactions depend only weakly on approximation schemes for the normal self-energy, required in present energy-desnity functional calculations, while pairing gaps from hard poentials are very sensitive to the effective-mass approximation scheme.