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@INPROCEEDINGS{Horns:408336,
      author       = {Horns, D. and Meyer, M.},
      title        = {{P}air-production opacity at high and very-high gamma-ray
                      energies},
      address      = {Hamburg},
      publisher    = {Verlag Deutsches Elektronen-Synchrotron},
      reportid     = {PUBDB-2018-02789, DESY-PROC-2013-04},
      isbn         = {978-3-935702-83-6},
      series       = {DESY-PROC},
      pages        = {77-80},
      year         = {2013},
      comment      = {Horns, D. "Pair-production opacity at high and very-high
                      gamma-ray energies" in Proceedings, 9th Patras Workshop on
                      Axions, WIMPs and WISPs (AXION-WIMP 2013) / Oberlack, Uwe,
                      Sissol, Pierre (eds.), 2013 ; AXION-WIMP 2013 : 9th Patras
                      Workshop on Axions, WIMPs and WISPs , 2013-06-23 -
                      2013-06-28, Mainz},
      booktitle     = {Horns, D. "Pair-production opacity at
                       high and very-high gamma-ray energies"
                       in Proceedings, 9th Patras Workshop on
                       Axions, WIMPs and WISPs (AXION-WIMP
                       2013) / Oberlack, Uwe, Sissol, Pierre
                       (eds.), 2013 ; AXION-WIMP 2013 : 9th
                       Patras Workshop on Axions, WIMPs and
                       WISPs , 2013-06-23 - 2013-06-28, Mainz},
      abstract     = {The propagation of high energy (HE,E$_γ >$ 100 MeV) and
                      very high-energy gammarays (VHE, E$_γ >$ 100 GeV) in the
                      extra-galactic photon field leads to pair- production and
                      consequently energy-and distance-dependent attenuation of
                      the primary intensity. The spectroscopy of an increasing
                      number of extra-galactic objects at HE and VHE energies has
                      demonstrated indeed the presence of such an attenuation
                      which in turn has been used to constrain the photon density
                      in the medium. At large optical depth $(\tau\gtrsim 2)$
                      potential modifications of pair-production due to competing
                      but rare processes (as, e.g., the presence of sub-neV axion-
                      like particle) may be found. Indications for a
                      pair-production anomaly have previously been found with
                      VHE-spectra. Here, we present further indications (at the
                      level of 3.68 $σ$) for a reduced optical depth at high
                      energies from an analysis of Fermi-LAT data.},
      month         = {Jun},
      date          = {2013-06-24},
      organization  = {9th Patras Workshop on Axions, WIMPs
                       and WISPs, Mainz (Germany), 24 Jun 2013
                       - 28 Jun 2013},
      keywords     = {Hypothetisches Teilchen (gnd)},
      cin          = {L},
      cid          = {I:(DE-H253)L-20120731},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      experiment   = {EXP:(DE-MLZ)NOSPEC-20140101},
      typ          = {PUB:(DE-HGF)29 / PUB:(DE-HGF)8 / PUB:(DE-HGF)7},
      doi          = {10.3204/DESY-PROC-2013-04/horns_dieter},
      url          = {https://bib-pubdb1.desy.de/record/408336},
}