ABSTRACT
The quasiparticle description makes sense only if the relaxation rate of the quasiparticles is much smaller than their energy. The relaxation of quasiparticle excitations is due to their mutual collisions and consequent decay into several others. Physically, the effect of the Pauli exclusion principle is felt only when the occupation probability of a given quantum state is of the order of unity. In the Maxwell-Boltzmann case, the probability of occupation of any quantum state is always small and hence Pauli's principle is not important. A natural question arises as to how the properties of a degenerate Fermi gas would change if the fermions interacted mutually. In the excited state, the momentum distribution of the particles will be different. The properties of a degenerate Fermi gas were first studied by Wilson-Sommerfeld in 1927. They turn out to be very different from a classical ideal gas.
