Because of the high energies and long distances to the sources, astrophysical observations provide a unique opportunity to test possible signatures of Lorentz invariance violation (LIV). Superluminal LIV enables the decay of photons at high energy. The high altitude water Cherenkov (HAWC) observatory is among the most sensitive gamma-ray instruments currently operating above 10 TeV. HAWC finds evidence of 100 TeV photon emission from at least four astrophysical sources. These observations exclude, for the strongest of the limits set, the LIV energy scale to $2.2\times {10}^{31}\mathrm{eV}$, over 1800 times the Planck energy and an improvement of 1 to 2 orders of magnitude over previous limits.

• Received 18 November 2019
• Revised 7 February 2020
• Accepted 4 March 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.131101