Three-Particle Correlation and the Off Energy-Shell Self-Energy of Excited Particles in a Fermion System of Hard Spheres

The energy shift in the ground state system of hard shoere fermions is studied with particular emphasis on the off energy-shell sefl energy effect of excited particled induced by three- aprticle correlation. The energy shift is known to diverge when one attenppts to analyze it in terms of K- or G-matrix which describes the two-particle coreelation successfully. Use is made of a new method which deals with the hard sphere interaction in terms of effective potential. The energy shift of tnterest is expressed as a convergent integral which varies as a^4log a for small values of the sphere radius a. The contribution to the integral of order a^4 is also identified