Identification of 3.55 KeV line in the framework of standard physics
  Identification of the X-ray 3.55 KeV line as a recombination line of $\pi^-$ tritium mesoatom is proposed. It has been shown that in principle it is possible to form such an atom under standard laboratory conditions, without bringing in new physics. 
V.K. Dubrovich
astro-ph.HE nucl-th