Astrophysical Limits on Lorentz Violation for Pions

TL;DR

This paper uses astrophysical observations of high-energy photons and pion decay to establish the first two-sided bounds on Lorentz violation for pions, constraining deviations in their maximum velocities at extremely small levels.

Contribution

It provides the first two-sided astrophysical bounds on Lorentz violation for pions, improving constraints on fundamental physics beyond previous nucleon-based limits.

Findings

Pions' maximum velocities are constrained to be within 1.5 x 10^(-11) of the speed of light.

High-energy photon observations limit pion velocity to be less than or equal to the speed of light at 2 x 10^(-9) level.

First two-sided bounds on Lorentz violation for pions derived from astrophysical data.

Abstract

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 --> pi^(+) + pi^(-) for up to 50 TeV photons constrains the possibility that pions' maximum achievable velocities are less than 1 at the 1.5 x 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 x 10^(-9) level. This provides the first two-sided bounds on Lorentz violation for pions.