Origin of cosmic gamma ray background

[wolram]

http://arxiv.org/abs/astro-ph/0506520

Title: Dark Matter Annihilation: the origin of cosmic gamma-ray background at 1-20 MeV
Authors: Kyungjin Ahn Eiichiro Komatsu
Comments: 5 pages, 3 figurs; submitted to PRD, Rapid Communication

The origin of the cosmic gamma-ray background at 1-20 MeV remains a mystery. We show that gamma-ray emission accompanying annihilation of 20 MeV dark matter particles explains most of the observed signal. Our model satisfies all of the current observational constraints, and naturally provides the origin of "missing" gamma-ray background at 1-20 MeV and 511 keV line emission from the Galactic center. We conclude that gamma-ray observations support the existence of 20 MeV dark matter particles. Improved measurements of the gamma-ray background in this energy band undoubtedly test our proposal.

 

[Nereid]

Good one wolfram!

I think this is the key phrase:

Our model satisfies all of the current observational constraints

Unfortunately, the present observational constraints are pretty mild indeed.

File this in the 'worth watching, review again when a lot more data becomes available' file?

 

[hellfire]

If annihilation events of dark matter particles with antiparticles take place in the present universe, then annihilation events should have been more frequent in past (due to higher density). This implies a background of radiation with wavelengths down to 1/z times (lets say 0.001, since recombination) the wavelength of the current gamma ray background. Shouldn't this be observable?

 

[Nereid]

If annihilation events of dark matter particles with antiparticles take place in the present universe, then annihilation events should have been more frequent in past (due to higher density). This implies a background of radiation with wavelengths down to 1/z times (lets say 0.001, since recombination) the wavelength of the current gamma ray background. Shouldn't this be observable?

Not necessarily.

First, if it's a 'line', then what line?

Second, the ancient 'space density' of DM recombination radiation has no strong constraints (unless the DM annihilation cross sections, densities, etc are well-constrained), so a lack of detection would put only the mildest limits on the parameter space (OK, I've not done the calculations; I'm working off the top of my head).

Finally, what do we know about the evolution of DM - particles, clumps, etc? I mean, for example, hasn't DM become more clumped (through self-gravity and baryonic clumping) through time than less?

 

[Chronos]

I'm sort of fond of the dark matter annihilation explanation. It is so convenient, I worry it might be too good to be true. Will report back after doing some homework.

 

[Garth]

May the gamma-ray background be modeled by a background of GRB's? The most likely model for those, based on the SWIFT observation, is that of a binary neutron star fusion into a BH.

Garth

 

[wolram]

Good one wolfram

.File this in the 'worth watching, review again when a lot more data becomes available' file?

Yes this seems to swing the swingometer to i am wrong, but as you say it is
to soon to be sure.