  We re-consider the self-energy of a nodal (Dirac) fermion in a 2D d-wave
superconductor. A conventional belief is that Im \Sigma (\omega, T) \sim max
(\omega^3, T^3). We show that \Sigma (\omega, k, T) for k along the nodal
direction is actually a complex function of \omega, T, and the deviation from
the mass shell. In particular, the second-order self-energy diverges at a
finite T when either \omega or k-k_F vanish. We show that the full summation of
infinite diagrammatic series recovers a finite result for \Sigma, but the full
ARPES spectral function is non-monotonic and has a kink whose location compared
to the mass shell differs qualitatively for spin-and charge-mediated
interactions.
