  We investigate the non-Fermi-liquid behaviors of the 2D and 3D Dirac/Weyl
systems with low-order and higher order dispersion. The self-energy correction,
symmetry, free energy, optical conductivity, density of states, and spectral
function are studied. We found that, for Dirac/Weyl systems with higher order
dispersion, the non-Fermi-liquid features remain even at finite chemical
potential, and they are distinct from the ones in Fermi-liquid picture and the
conventional non-Fermi-liquid picture. The Landau damping of the longitudinal
excitations within random-phase-approximation (RPA) for the non-Fermi-liquid
case are also discussed.
