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Gamma ray Astrophysics, the Extragalactic Background Light, and New Physics.

DE2008938459

Publication Date	2008
Personal Author	Serpico, P. D.
Page Count	6
Abstract	Very high energy gamma-rays are expected to be absorbed by the extragalactic background light over cosmological distances via the process of electron-positron pair production. However, recent observations of cosmologically distant emitters by ground based gamma-ray telescopes might be indicative of a higher-than-expected degree of transparency of the universe. One mechanism to explain this observation is the oscillation between photons and axion-like-particles (ALPs). Here we explore this possibility, focusing on photon-ALP conversion in the magnetic fields in and around gamma-ray sources and in the magnetic field of the Milky Way, where some fraction of the ALP flux is converted back into photons. We show that this mechanism can be efficient in allowed regions of the ALP parameter space, as well as in typical configurations of the Galactic Magnetic Field. As case example, we consider the spectrum observed from a HESS source. We also discuss features of this scenario which could be used to distinguish it from standard or other exotic models.
Keywords	Gamma rays Astrophysics Background radiation Light(Visible radiation) Axions Cosmology Telescopes Magnetic fields Photons Universe Oscillations
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Fermi National Accelerator Lab., Batavia, IL.; Department of Energy, Washington, DC.
Supplemental Notes	Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200907

Gamma ray Astrophysics, the Extragalactic Background Light, and New Physics.

Gamma ray Astrophysics, the Extragalactic Background Light, and New Physics.
DE2008938459

Publication Date	2008
Personal Author	Serpico, P. D.
Page Count	6
Abstract	Very high energy gamma-rays are expected to be absorbed by the extragalactic background light over cosmological distances via the process of electron-positron pair production. However, recent observations of cosmologically distant emitters by ground based gamma-ray telescopes might be indicative of a higher-than-expected degree of transparency of the universe. One mechanism to explain this observation is the oscillation between photons and axion-like-particles (ALPs). Here we explore this possibility, focusing on photon-ALP conversion in the magnetic fields in and around gamma-ray sources and in the magnetic field of the Milky Way, where some fraction of the ALP flux is converted back into photons. We show that this mechanism can be efficient in allowed regions of the ALP parameter space, as well as in typical configurations of the Galactic Magnetic Field. As case example, we consider the spectrum observed from a HESS source. We also discuss features of this scenario which could be used to distinguish it from standard or other exotic models.
Keywords	Gamma rays Astrophysics Background radiation Light(Visible radiation) Axions Cosmology Telescopes Magnetic fields Photons Universe Oscillations
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Fermi National Accelerator Lab., Batavia, IL.; Department of Energy, Washington, DC.
Supplemental Notes	Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200907