  We consider the effect of Coulomb interactions on the average density of
states (DOS) of disordered low-dimensional metals for temperatures T and
frequencies omega smaller than the inverse elastic life-time. Using the fact
that long-range Coulomb interactions in two dimensions (2d) generate
ln^2-singularities in the DOS nu (omega) but only ln-singularities in the
conductivity sigma(omega), we can re-sum the most singular contributions to the
average DOS via a simple gauge-transformation. If lim_{omega -> 0} sigma
(omega) > 0, then a metallic Coulomb gap nu(omega) propto |omega|/e^4 appears
in the DOS at T=0 for frequencies below a certain crossover frequency Omega_2
which depends on the value of the DC conductivity sigma(0). Here, -e is the
charge of the electron. Naively adopting the same procedure to calculate the
DOS in quasi 1d metals, we find nu(omega) propto (|omega|/Omega_1)^{1/2}
exp(-Omega_1/|omega|) at T = 0, where Omega_1 is some interaction-dependent
frequency scale. However, we argue that in quasi 1d the above
gauge-transformation method is on less firm grounds than in 2d. We also discuss
the behavior of the DOS at finite temperatures and give numerical results for
the expected tunneling conductance that can be compared with experiments.
