Origin of cosmic gamma ray background

In summary, the authors propose that the gamma-ray background at 1-20 MeV is explained by the annihilation of 20 MeV dark matter particles. This model satisfies all of the current observational constraints, and provides a natural explanation for "missing" gamma-ray background at 1-20 MeV and 511 keV line emission from the Galactic center.
  • #1
wolram
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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.
 
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  • #2
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?
 
  • #3
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?
 
  • #4
hellfire said:
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?
 
  • #5
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.
 
  • #6
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
 
  • #7
Nereid said:
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.
 

1. What is the cosmic gamma ray background?

The cosmic gamma ray background (CGB) is a diffuse glow of high-energy photons that permeates the entire universe. These photons have wavelengths shorter than 0.1 nanometers and are the most energetic form of light. The CGB is believed to be a remnant of the early universe and is an important source of information about the history of our universe.

2. How was the cosmic gamma ray background discovered?

The CGB was first detected in the 1960s by scientists studying the cosmic microwave background (CMB). They noticed that the CMB was not completely uniform and that there were small fluctuations in its intensity. Further investigations revealed that these fluctuations were caused by the presence of the CGB.

3. What is the origin of the cosmic gamma ray background?

The exact origin of the CGB is still a subject of research and debate among scientists. Some theories suggest that it is produced by the interactions of high-energy particles with radiation in the early universe. Others propose that it is the result of the emission of gamma rays from distant objects such as active galactic nuclei and supernovae.

4. How does the cosmic gamma ray background affect our understanding of the universe?

Studying the CGB allows us to better understand the processes that occurred in the early universe, such as the formation of stars and galaxies. It also provides insights into the distribution of matter and energy in the universe and the evolution of these structures over time. Additionally, the CGB can reveal information about the properties of high-energy particles and the nature of dark matter.

5. How do scientists study the cosmic gamma ray background?

Scientists use a variety of instruments, such as telescopes and satellites, to study the CGB. These instruments detect and measure the intensity and energy of gamma rays coming from different regions of the sky. By analyzing this data, scientists can create maps of the CGB, identify its sources, and understand its properties and evolution.

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