Lorentz Invariance Violation and Space–Time Symmetry Breaking

Dear Colleagues,

Lorentz invariance is one of the fundamental principles of Einstein's relativity and quantum field theories. In most of the standard models of modern physics, it is assumed to be an exact symmetry that should be preserved at all scales. This idea is supported by a lot of remarkably precise Earth-based laboratory experiments, with no violations detected to date. However, there are many new models of physics beyond the standard model with various interesting mechanisms, some of which, especially quantum gravity (QG) theories, have provoked a violation of Lorentz invariance. In these models, the effects arising from the microscopic fabric of space–time are expected to appear at distances of the order of the Planck length. For more than 30 years, studies unraveling the nature of quantum gravity/space–time through violations of Lorentz (LV) and charge-parity-time symmetry (CPTV) have attracted significant attention from both theoretical and phenomenological perspectives, given that they can provide intriguing hints at physics beyond relativity, and may eventually allow a breakthrough paradigm shift from our current understanding of the fundamental structure of space–time. In terms of theoretical work, different types of effective theories of QG have been explored to investigate the origin and the consequence of these symmetry violations. These include low-energy effective field theory models, bottom-up scenarios, such as doubly special relativity, and top-down methods involving non-local stringy or membrane-like objects that naturally include the graviton as an ingredient, or a loop approach to canonical quantum gravity. Different theories yield quite distinct phenomenological predictions. Delays in the time of flight of massless particles, e.g.,  photons or ultrarelativistic neutrinos, can be a signature for almost all of them. However, other constraints, such as modification or appearance of reaction thresholds, or birefringence effects, do not apply in the same way. On the experimental side, this leads to the establishment of constraints for high-energy LVs in dispersion relations for different particles through astrophysical observations. From the phenomenological side, this leads to new possible theoretical interpretations regarding the potential of finding authentic signatures for quantum gravity from experiments.

This Special Issue is devoted to both the presentation of new results on the observational constraints on LV and CPTV (and, presumably, on the underlying QG), and the overview of theoretical and experimental aspects of space–time symmetry breaking and departures from CPT and Lorentz invariance, involving at least: quantum field theory and gravitation, particle (astro)physics, phenomenologies of theories beyond the standard model, origins and mechanisms of Lorentz and/or CPT violation, and Finsler geometry and its mathematical foundations.

Prof. Dr. Bo-Qiang Ma
Dr. Chengyi Li
Guest Editors

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• Lorentz invariance violation
• CPT symmetry violation
• spontaneous symmetry breaking
• space–time symmetries
• quantum gravity
• phenomenology of physics beyond the standard model
• astroparticle physics and cosmology
• test of Einstein's relativity