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The basic hypothesis is that if what looks like a geometric continuum actually arose from myriad nongeometric entities then there will be DEFECTS (on which light can scatter.)

Traveling over cosmological distances a photon may SCATTER on such imperfections with a certain cross-section probability. Hossenfelder finds that it can be knocked this and that in such a way that effects cancel and on average there is

**no Lorentz violation**---no dispersion on average.

Besides Lorentz violation, she identifies other observable effects depending parameters that are constrained by CMB data already collected. She plots the portions of parameter space which are still open, not having been ruled out so far.

The work is in two parts.

http://arxiv.org/abs/1309.0311

**Phenomenology of Space-time Imperfection I: Nonlocal Defects**

Sabine Hossenfelder

(Submitted on 2 Sep 2013)

If space-time is emergent from a fundamentally non-geometric theory it will generically be left with defects. Such defects need not respect the locality that emerges with the background. Here, we develop a phenomenological model that parameterizes the effects of nonlocal defects on the propagation of particles. In this model, Lorentz-invariance is preserved on the average. We derive constraints on the density of defects from various experiments.

25 pages, 7 figures

http://arxiv.org/abs/1309.0314

**Phenomenology of Space-time Imperfection II: Local Defects**

Sabine Hossenfelder

(Submitted on 2 Sep 2013)

We propose a phenomenological model for the scattering of particles on space-time defects in a treatment that maintains Lorentz-invariance on the average. The local defects considered here cause a stochastic violation of momentum conservation. The scattering probability is parameterized in the density of defects and the distribution of the momentum that a particle can obtain when scattering on the defect. We identify the most promising observable consequences and derive constraints from existing data.

18 pages, 5 figures