Photon-photon dispersion of TeV gamma rays and its role for photon-ALP conversion
Abstract
The propagation of TeV gamma rays can be strongly modified by B -field induced conversion to axionlike particles (ALPs). We show that, at such high energies, photon dispersion is dominated by background photons—the only example where photon-photon dispersion is of practical relevance. We determine the refractive index for all energies and find that, for fixed energy density, background photons below the pair-production threshold dominate. The cosmic microwave background alone provides an "effective photon mass" of mγ2=-(1.01 neV ×ω /TeV )2 for ω ≲1000 TeV . The extragalactic background light is subdominant, but local radiation fields in the Galaxy or the source regions provide significant contributions. Photon-photon dispersion is small enough to leave typical scenarios of photon-ALP oscillations unscathed, but big enough to worry about it case by case.
- Publication:
-
Physical Review D
- Pub Date:
- April 2015
- DOI:
- 10.1103/PhysRevD.91.083003
- arXiv:
- arXiv:1412.4777
- Bibcode:
- 2015PhRvD..91h3003D
- Keywords:
-
- 95.85.Pw;
- 14.70.Bh;
- 14.80.Va;
- 98.70.Rz;
- gamma-ray;
- Photons;
- gamma-ray sources;
- gamma-ray bursts;
- Astrophysics - High Energy Astrophysical Phenomena;
- High Energy Physics - Phenomenology
- E-Print:
- v1 - 5 pages, 3 figures. v2 - title expanded, text improved for clarity, identical to published version. v3 - Typographical corrections explained in footnotes 1 and 2. v4 - Correction of Eq.(11) as explained in footnote 4, no change of conclusions