I wrote: Just one point of detail -- I read Va'vra as saying that if you sum all of > the photon energies from a hydrogen atom going to DDL across a full solid > angle, this will add up to 511 keV. >
Looking at the 2013 paper again, that is just one of two possibilities. One possibility is that the DDL gives off a 511 keV emission (explaining the signal in the cosmic background) and the other is that the DDL emissions sum up over a solid angle (not explaining the signal, presumably) [1]. He does something similar with the capture cross section of DDL hydrogen -- it might or might not be all that high (p. 6). Eric [1] http://arxiv.org/pdf/1304.0833v3.pdf, p. 5
