We describe an approach to the theory of the Fermi surface based on the renormalization group. A notion of the quasiparticle appears naturally in the theory. The \ensuremath{\beta} function is finite to all orders of the perturbation theory and we compute and discuss it to second order. The normality of the Fermi surface is linked to the repulsivity of the quasiparticle potential; the remarkable cancellations that occur in the \ensuremath{\beta} function lead one to think that a normal Fermi surface can perhaps occur, but only when the interaction between the quasiparticles is repulsive. The approach was first proposed in an earlier paper and we give an improved version of it here referring to the earlier work only to make use of technical estimates derived there.
Two-loop renormalization-group (RG) analysis for a two-dimensional electron system with a partially flat Fermi surface has been carried out. We found that the RG flow of the quasiparticle weight depends on the location of the electron wave number
k on the Fermi surface due to the kinematical restriction to the logarithmically divergent processes in the flat regions of the Fermi surface.
We study equilibrium and nonequilibrium aspects of the normal state of cold and dense QCD and QED. The exchange of dynamically screened magnetic gluons (photons) leads to infrared singularities in the fermion propagator for excitations near the Fermi surface and the breakdown of the Fermi liquid description. We implement a resummation of these infrared divergences via the Euclidean renormalization group to obtain the spectral density, dispersion relation, widths, and wave function renormalization for single quasiparticles near the Fermi surface. We find that all features scale with anomalous dimensions: ${\ensuremath{\omega}}_{p}(k)\ensuremath{\propto}|k\ensuremath{-}{k}_{F}{|}^{1/(1\ensuremath{-}2\ensuremath{\lambda})},$ $\ensuremath{\Gamma}(k)\ensuremath{\propto}|k\ensuremath{-}{k}_{F}{|}^{1/(1\ensuremath{-}2\ensuremath{\lambda})};$ ${Z}_{p}(k)\ensuremath{\propto}|k\ensuremath{-}{k}_{F}{|}^{2\ensuremath{\lambda}/(1\ensuremath{-}2\ensuremath{\lambda})}$ with $\ensuremath{\lambda}=\ensuremath{\alpha}/6\ensuremath{\pi}$ for QED, $({\ensuremath{\alpha}}_{s}/6\ensuremath{\pi}{)(N}_{c}^{2}\ensuremath{-}{1)/2N}_{c}$ for QCD with
Nc colors and
NF flavors. The discontinuity of the quasiparticle distribution at the Fermi surface vanishes. For $k\ensuremath{\approx}{k}_{F}$ we find ${n}_{k\ensuremath{\approx}{k}_{F}}=\mathrm{sin}[\ensuremath{\pi}\ensuremath{\lambda}]/2\ensuremath{\pi}\ensuremath{\lambda}\ensuremath{-}(k\ensuremath{-}{k}_{F})/\ensuremath{\pi}M(1\ensuremath{-}4\ensuremath{\lambda})+\mathcal{O}(k\ensuremath{-}{k}_{F}{)}^{2}$ with
M the dynamical screening scale of magnetic gluons (photons). The dynamical renormalization group is implemented to study nonequilibrium relaxation. The amplitude of single quasiparticle states with momentum near the Fermi surface falls off as $|{\ensuremath{\Psi}}_{k\ensuremath{\approx}{k}_{F}}(t)|\ensuremath{\approx}|{\ensuremath{\Psi}}_{k\ensuremath{\approx}{k}_{F}}{(t}_{0})|{e}^{\ensuremath{-}\ensuremath{\Gamma}(k)(t\ensuremath{-}{t}_{0})}[{t}_{0}/t{]}^{2\ensuremath{\lambda}}.$ Thus quasiparticle states with Fermi momentum have zero group velocity and relax with a power law with a coupling-dependent anomalous dimension.