Tunneling into Extra Dimension and High-Energy Violation of Lorentz Invariance

TL;DR

This paper explores models with infinite extra dimensions where Lorentz invariance emerges at low energies, revealing that particles are resonances with energy-dependent widths and maximum speeds are generally less than the bulk speed.

Contribution

It introduces a class of models with infinite extra dimensions where Lorentz invariance is approximate and discusses the properties of particles as resonances with finite widths.

Findings

Maximum speeds of particles are equal and below the bulk speed.

Particles are resonances with widths depending on energy.

Lorentz invariance emerges as an approximate symmetry at low energies.

Abstract

We consider a class of models with infinite extra dimension, where bulk space does not possess SO(1,3) invariance, but Lorentz invariance emerges as an approximate symmetry of the low-energy effective theory. In these models, the maximum attainable speeds of the graviton, gauge bosons and scalar particles are automatically equal to each other and smaller than the maximum speed in the bulk. Additional fine-tuning is needed in order to assure that the maximum attainable speed of fermions takes the same value. A peculiar feature of our scenario is that there are no truly localized modes. All four-dimensional particles are resonances with finite widths. The latter depends on the energy of the particle and is naturally small at low energies.