Lorentz invariance and quantum gravity: an additional fine-tuning problem?

TL;DR

This paper discusses the challenge of maintaining Lorentz invariance in quantum gravity theories, highlighting that without fine-tuning, violations could be significantly larger than previously thought, emphasizing the need for mechanisms that preserve Lorentz symmetry.

Contribution

It reveals that combining elementary particle interactions with a Planck-scale preferred frame leads to large Lorentz violations unless fine-tuned, stressing the importance of theoretical mechanisms to preserve invariance.

Findings

Lorentz violation could be 20 orders of magnitude higher than earlier estimates.

Fine-tuning of parameters is required to suppress Lorentz violation.

The search for mechanisms preserving Lorentz invariance is crucial.

Abstract

Trying to combine standard quantum field theories with gravity leads to a breakdown of the usual structure of space-time at around the Planck length, 1.6*10^{-35} m, with possible violations of Lorentz invariance. Calculations of preferred-frame effects in quantum gravity have further motivated high precision searches for Lorentz violation. Here, we explain that combining known elementary particle interactions with a Planck-scale preferred frame gives rise to Lorentz violation at the percent level, some 20 orders of magnitude higher than earlier estimates, unless the bare parameters of the theory are unnaturally strongly fine-tuned. Therefore an important task is not just the improvement of the precision of searches for violations of Lorentz invariance, but also the search for theoretical mechanisms for automatically preserving Lorentz invariance.