Weakness of accelerator bounds on electron superluminality without a preferred frame

TL;DR

This paper critically examines the bounds on electron superluminality derived from laboratory experiments, highlighting their dependence on a preferred frame and showing that in theories with deformed Lorentz symmetry, these bounds are significantly weaker than previously assumed.

Contribution

It demonstrates that laboratory bounds on electron superluminality rely on assumptions of a preferred frame and are weaker in theories with deformed Lorentz symmetry, challenging their effectiveness.

Findings

In-vacuo Cherenkov processes are forbidden in theories with deformed Lorentz symmetry.

Synchrotron power measurements provide weak bounds on Lorentz symmetry deformation.

Laboratory bounds on electron superluminality are limited and less constraining than previously thought.

Abstract

The reference laboratory bounds on superluminality of the electron are obtained from the absence of in-vacuo Cherenkov processes and the determinations of synchrotron radiated power for LEP electrons. It is usually assumed that these analyses establish the validity of a standard special-relativistic description of the electron with accuracy of at least a few parts in $10^{14}$, and in particular this is used to exclude electron superluminality with such an accuracy. We observe that these bounds rely crucially on the availability of a preferred frame. In-vacuo-Cherenkov processes are automatically forbidden in any theory with "deformed Lorentz symmetry", relativistic theories that, while different from Special Relativity, preserve the relativity of inertial frames. Determinations of the synchrotron radiated power can be used to constrain the possibility of Lorentz-symmetry deformation, but provide rather weak bounds, which in particular for electron superluminality we establish to afford us no more constraining power than for an accuracy of a few parts in $10^4$. We argue that this observation can have only a limited role in the ongoing effort of analysis of the anomaly tentatively reported by the OPERA collaboration, but we stress that it could provide a valuable case study for assessing the limitations of "indirect" tests of fundamental laws of physics.