  Using a unified approach employing a homogeneous Lippmann-Schwinger-type
equation satisfied by resonance functions and basic facts on Riesz potentials,
we discuss the absence of threshold resonances for Dirac and Schrodinger
operators with sufficiently short-range interactions in general space
dimensions.
  More specifically, assuming a sufficient power law decay of potentials, we
derive the absence of zero-energy resonances for massless Dirac operators in
space dimensions $n \geq 3$, the absence of resonances at $\pm m$ for massive
Dirac operators (with mass $m > 0$) in dimensions $n \geq 5$, and recall the
well-known case of absence of zero-energy resonances for Schr\"odinger
operators in dimension $n \geq 5$.
