  We study a method by which realistic nucleon-nucleon potentials V_NN can be
reduced, in a physically equivalent way, to an effective low-momentum potential
V-low-k confined within a cut-off momentum k-cut. Our effective potential is
obtained using the folded-diagram method of Kuo, Lee and Ratcliff, and it is
shown to preserve the half-on-shell T-matrix. Both the Andreozzi-Lee-Suzuki and
the Andreozzi-Krenciglowa-Kuo iteration methods have been employed in carrying
out the reduction. Calculations have been performed for the Bonn A and Paris NN
potentials, using various choices for k-cut such as 2 fm-1. The deuteron
binding energy, low-energy NN phase shifts, and the low-momentum half-on-shell
T-matrix given by V_NN are all accurately reproduced by V-low-k. Possible
applications of V-low-k directly to nuclear matter and nuclear structure
calculations are discussed.
