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- Lorentz symmetry: Broken, intact or deformed?

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12100108

* 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.

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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 Lorentz-invariance in this scenario.

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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.

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* in Horava-Lifshiftz gravity*Horava-Lifshitz 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.

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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 scale-invariant sprectrum of fluctuation may arise, even without inflation. Distinct observational imprints may be left.

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*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

©2012 Perimeter Institute for Theoretical Physics