Lorentz symmetry: Broken, intact or deformed? Speaker(s): Niayesh Afshordi, David Mattingly, Rafael Sorkin, Sabine Hossenfelder, Jurek KowalskiGlikman, Stefano Liberati, Joao Magueijo, Daniel Sudarsky
Abstract: Is aether technically natural?
I will discuss whether higher energy Lorentz violation should be considered a natural expectation in theories of quantum gravity with a preferred frame. _____________________________ If spacetime is a causal set then Lorentz symmetry is unbroken _____________________________ Quantum superpositions of the speed of light If the metric is an operator, it can exist in superpositions. The simplest case one can look at is a superposition of flat spaces which differ only in the value of the speed of light. I will lay out how such superpositions can be incorporated into quantum field theory, and discuss the fate of Lorentzinvariance in this scenario. _________________________________ Relative locality and fate of Lorentz symmetry In my talk I will briefly introduce the idea of relative locality, being a particular regime of quantum gravity characterized by negligible Planck length and finite Planck mass. Then I will discuss possible scenarios concerning the fate of Lorentz symmetry in this regime. _________________________________ Observational constraints on scale hierarchy in HoravaLifshiftz gravity HoravaLifshitz gravity models contain higher order operators suppressed by a characteristic scale, which is required to be parametrically smaller than the Planck scale. We show that recomputed synchrotron radiation constraints from the Crab nebula suffice to exclude the possibility that this scale is of the same order of magnitude as the Lorentz breaking scale in the matter sector. This highlights the need for a mechanism that suppresses the percolation of Lorentz violation in the matter sector and is effective for higher order operators as well. __________________________________ Breaking Lorentz invariance: the Universe loves it! I show how the local Lorentz and / or diffeomorphism invariances may be broken by a varying speed of light, softly or harshly, depending on taste. Regardless of the fundamental implications of such dramas, these smmetry breakings may be of great practical use in cosmology. They may solve the horizon and flatness problesm. A near scaleinvariant sprectrum of fluctuation may arise, even without inflation. Distinct observational imprints may be left. _________________________________ Quantum Gravity Phenomenology without Lorentz Invariance Violation Is there hope to see quantum gravity effects if the underlying theory is strictly respecting of Lorentz invariance? I will discuss a novel class of possibilities, suggested by analogy with some simple solid state physics, including one that has lead to an actual experiment, which has placed the first relevant constraints on these kind of effects Date: 24/10/2012  3:30 pm
Collection: Experimental Search for Quantum Gravity 2012
