Marginal Fermi liquid behavior at the onset of 2k_F density wave order in two-dimensional metals with flat hot spots

We analyze quantum fluctuation effects at the onset of incommensurate 2k_F charge- or spin-density-wave

order in two-dimensional metals for a model in which the ordering wave vector Q connects a single pair of hot

spots on the Fermi surface with a vanishing Fermi surface curvature. The tangential momentum dependence of

the bare dispersion near the hot spots is proportional to |kt|^α with α > 2. We first compute the order parameter

susceptibility and the fermion self-energy in a random phase approximation (RPA). Logarithmic divergences are

subsequently treated by a renormalization-group analysis. The coupling between the order parameter fluctuations

and the fermions vanishes logarithmically in the low-energy limit. As a consequence, the logarithmic divergences

found in the RPA do not sum up to anomalous power laws. Instead, only logarithmic corrections to Fermi liquid

behavior are obtained. In particular, the quasiparticle weight and the Fermi velocity vanish logarithmically at the

hot spots.