Astrophysical limits on Lorentz violation for pions

Pions, like nucleons, are composed primarily of up and down quarks and gluons. Constraints on spin-independent Lorentz violation in the proton, neutron, and pion sectors translate into bounds on Lorentz violation for the fundamental fields. The best bounds on pion Lorentz violation come from astrophysical measurements. The absence of the absorption process $\gamma \to {\pi }^{+}+{\pi }^{-}$ for up to 50 TeV photons constrains the possibility that pions’ maximum achievable velocities are less than 1 at the $1.5\times {10}^{-11}$ level. The fact that pions with energies up to 30 TeV are observed to decay into photons rather than hadrons bounds the possibility of a maximum velocity greater than 1 at the $2\times {10}^{-9}$ level. This provides the first two-sided bounds on Lorentz violation for pions.