Limits on Neutron Lorentz Violation from the Stability of Primary Cosmic Ray Protons

TL;DR

This paper uses the stability of ultra-high-energy cosmic ray protons to set new bounds on neutron Lorentz violation coefficients, significantly improving constraints on hadron and pion Lorentz violations.

Contribution

It provides first-time bounds on six neutron Lorentz violation coefficients and improves constraints on neutral pion violations by eleven orders of magnitude.

Findings

Bound six neutron coefficients at 5 x 10^(-14) level.

Set the first constraints on spin-independent boost anisotropy for neutrons.

Achieved bounds on neutral pions at 4 x 10^(-21) level.

Abstract

Recent evidence appears to confirm that the ultra-high-energy primary cosmic ray spectrum consists mostly of protons. The fact that these protons can traverse large distances to reach Earth allows us to place bounds on Lorentz violations. The protons neither emit vacuum Cerenkov radiation nor $\beta$-decay into neutrons, and this constrains six previously unmeasured coefficients in the neutron sector at the 5 x 10^(-14) level. Among the coefficients bounded here for the first time are those that control spin-independent boost anisotropy for neutrons. This is a phenomenon which could have existed (in light of the preexisting bounds) without additional fine tuning. There are also similar bounds for others species of hadrons. The bounds on Lorentz violation for neutral pions are particularly strong, at the 4 x 10^(-21) level, eleven orders of magnitude better than previous constraints.