Limits on Lorentz violation from charged-pion decay

TL;DR

This paper investigates potential Lorentz violation effects in charged-pion decay using an effective field theory framework, deriving decay rate formulas and establishing bounds on quark sector parameters to guide future experimental tests.

Contribution

It introduces a method to relate quark sector Lorentz violation to lepton and W-boson sectors, enabling bounds on quark parameters for the first time.

Findings

Bounds of order 10^{-4} on first-generation quark Lorentz violation parameters.

Derived differential pion-decay rate including muon polarization effects.

Provided a formula to constrain Lorentz violation in future experiments.

Abstract

Charged-pion decay offers many opportunities to study Lorentz violation. Using an effective field theory approach, we study Lorentz violation in the lepton, W-boson, and quark sectors and derive the differential pion-decay rate, including muon polarization. Using coordinate redefinitions we are able to relate the first-generation quark sector, in which no bounds were previously reported, to the lepton and W-boson sector. This facilitates a tractable calculation, enabling us to place bounds on the level of $10^{-4}$ on first-generation quark parameters. Our expression for the pion-decay rate can be used to constrain Lorentz violation in future experiments.