  A Dirac metal is a doped (gated) Dirac material with the Fermi energy
($E_\text{F}$) lying either in the conduction or valence bands. In the
non-interacting picture, optical absorption in gapless Dirac metals occurs only
if the frequency of incident photons ($\Omega$) exceeds the direct (Pauli)
frequency threshold, equal to $2E_\text{F}$. In this work, we study, both
analytically and numerically, the role of electron-electron ($ee$) and
electron-hole ($eh$) interactions in optical absorption of two-dimensional (2D)
and three-dimensional (3D) Dirac metals in the entire interval of frequencies
below $2E_\text{F}$. We show that, for $\Omega\ll E_\text{F}$, the optical
conductivity, $\Re\sigma(\Omega)$, arising from the combination of $ee$ and
certain $eh$ scattering processes, scales as $\Omega^2\ln\Omega$ in 2D and as
$\Omega^2$ in 3D, respectively, both for short-range (Hubbard) and long-range
(screened Coulomb) interactions. Another type of $eh$ processes, similar to
Auger-Meitner (AM) processes in atomic physics, starts to contribute for
$\Omega$ above the direct threshold, equal to $E_\text{F}$. Similar to the case
of doped semiconductors with parabolic bands studied in prior literature, the
AM contribution to $\Re\sigma(\Omega)$ in Dirac metals is manifested by a
threshold singularity, $\Re\sigma(\Omega)\propto (\Omega-E_\text{F})^{d+2}$,
where $d$ is the spatial dimensionality and $0<\Omega-E_\text{F}\ll
E_\text{F}$. In contrast to doped semiconductors, however, the AM contribution
in Dirac metals is completely overshadowed by the $ee$ and other $eh$
contributions. Numerically, $\Re\sigma(\Omega)$ happens to be small in almost
the entire range of $\Omega<2E_\text{F}$. This finding may have important
consequences for collective modes in Dirac metals lying below $2E_\text{F}$.
