The Landau Parameter of the Cubic Dispersion Term of the Energy Spectrum of Liquid ⁴He

Abstract

The expression for the energy shift from the Feynman spectrum of liquid ⁴He is obtained up to the cubic term in the wave number p at very low wave numbers by expanding the coherent factors involved in the previous expression of the energy shift. The result obtained here gives rise to a shift of only the cubic dispersion term of the Feynman spectrum keeping the linear term of the wave number p unchanged. The Landau parameter of the energy spectrum denoted by γ remains negative, in other words the spectrum is concave at very low wave numbers.