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This video is about two-photon (gamma-gamma) physics, and how photons can interact with each other - either mediated by a passing lepton, or gravitationally via lensing, or via vacuum fluctuation pair production of vertical particles (electron-positron pair, for example). This is the so-called "box diagram" feynman diagram.

REFERENCES

Water waves interact with each other (weakly nonlinear shallow water waves)
https://en.wikipedia.org/wiki/....Korteweg%E2%80%93deV
http://mathworld.wolfram.com/K....orteweg-deVriesEquat

Paper: Absorption of Very High Energy Gamma Rays in the Milky Way
https://arxiv.org/pdf/1608.01587.pdf

Paper: Observing light-by-light scattering at the Large Hadron Collider (LHC)
https://arxiv.org/pdf/1305.7142.pdf

Mass-Energy Scale
http://labs.minutelabs.io/Mass-Energy-Scale/

Optical Depth
https://en.wikipedia.org/wiki/Opticaldepth

The electromagnetic spectrum and photon energies
http://labman.phys.utk.edu/phy....s222core/modules/m6/

Gravitational Lensing
http://andybohn.com/research/lensing.html

Ask an Astrophysicist on gamma ray scattering and energies in cosmology
http://teacherlink.ed.usu.edu/....tlnasa/reference/ima

Measuring Vacuum Polarisation with High Power Lasers
https://arxiv.org/pdf/1510.08456.pdf

Detecting vacuum birefringence with X-ray free electron lasers and high-power optical lasers
https://indico.desy.de/indico/....event/12654/session/

Vacuum birefringence in the head-on collision of XFEL and optical high-intensity laser pulses
https://arxiv.org/pdf/1807.03302.pdf

ATLAS makes first direct detection of Light-by-light scattering at the LHC
https://atlas.cern/updates/pre....ss-statement/atlas-s

Two Photon Physics
http://www.hep.ucl.ac.uk/opal/....gammagamma/gg-tutori
https://en.wikipedia.org/wiki/Two-photonphysics

Thesis: The Opacity of the Universe for high and very high energy γ-rays
http://inspirehep.net/record/1....254304/files/desy-th



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