MG14 - Talk detail

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Talk

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Abstract

The purpose of the talk is to discuss possible empirical consequences of the Causal Dynamical Triangulations (CDT) approach to quantum gravity. The analysis will be based on two characteristic features of CDT: the dimensional reduction and the non-trivial phase structure. In the first case, quantum modified dispersion relation for a test field will be reconstructed based on numerical analysis of a discrete diffusion process defined on simplicial geometry of CDT. The obtained dispersion relation allows to study impact of the quantum gravity effects on propagation of astrophysical photons and primordial cosmological perturbations. Both possibilities will be discussed in the talk. As we will show, Fermi satellite observations allow to rule out a possibility of "low-energy" (below around 10 EeV) dimensional reduction. In case of the primordial cosmological perturbations, it will be demonstrated that for a scenario when length scale of dimensional reduction exceeds the Hubble radius the nearly scale-invariant scalar perturbations might arise from the vacuum state. However, the predicted magnitude of deviation from the scale-invariance is in contradiction with the up to date Planck and BICEP2 results. Other scenarios, which are not in conflict with observations, are still possible. A yet different possibility is given by a higher-order gravitational phase transition, which has been observed in CDT. The phase transition interpolates between a non-geometric crumpled phase of gravity, and an extended phase with classical properties. We will discuss whether the phase transition might generate primordial perturbations which are consistent with cosmological observations.

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