Exchange Effects and the Dynamics of $^3$He

Abstract = {{The ground state of strongly interacting Fermi fluids, specifically $^3$He, is well understood, using either simulation or correlated basis function techniques. However, the manifestly microscopic determination of the dynamics of such systems still poses a number of open problems. One of these is the importance of exchange effects in the density channel. The subject of this work is to clarify this question. We demonstrate here that exchange effects are, even in the density channel, not negligible. The main consequence is a lowering of the collective mode toward the particle-hole continuum in agreement with recent measurements on $^3$He. In the experiment also a strong damping of the collective mode is observed. Our results show that we should, by including self-energy corrections and multipair-fluctuations, be able to determine conclusively the many-particle aspects of that effect.}}