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The recently discovered phenomenon of the Universe's accelerated expansion is a rare window of opportunity into the **fundamental nature of gravitational physics**.

The goal of this project is two-fold:

On one hand, the project aims at maximally exploiting the above window to understand the implications of the accelerated stage and its agent, **dark energy**, for the fundamental nature of gravitational interactions at the **largest observable distances**.

On the other hand, the set of consistent theories leading to large distance deformations of gravity will be investigated, by combining principles of mathematical elegance (e.g. general covariance) and simplicity with powerful field-theoretical criteria, such as, **unitarity**, **causality**, **t'Hooft naturalness** and the well-understood properties of **classical black hole physics**.

In particular interesting are theories in which the dimensionality of space-time
effectively changes on cosmological scales. There are strong indications from previous studies that consistent theories with **deformed graviton dynamics** in the far infrared belong to this class of models.

With the advent of more and more powerful cosmological large-scale probes, **experimentally testable predictions** will confront the **theoretical model building**.

[1] F.Berkhahn, S.Hofmann, F.Kuhnel, P.Moyassari and D.Dietrich,
**Island of Stability for Consistent Deformations of Einstein's Gravity**,
arXiv:1106.3566 [hep-th], **accepted for publication in Phys. Rev. Lett.**

[2] F.Berkhahn, D.D.Dietrich and S.Hofmann,
**Consistency of Relevant Cosmological Deformations on all Scales**,
arXiv:1104.2534 [hep-th], **JCAP 1109 (2011) 024**

[3] G.Dvali, C.Gomez and A.Kehagias,
**Classicalization of Gravitons and Goldstones**,
arXiv:1103.5963 [hep-th], **JHEP 1111 (2011) 070**

[4] F.Berkhahn, D.D.Dietrich and S.Hofmann,
**Cosmological Classicalization: Maintaining Unitarity under Relevant Deformations**
**of the Einstein-Hilbert Action**,
arXiv:1102.0313 [hep-th],
**Phys. Rev. Lett. 106 (2011) 191102**

[5] G.Dvali, C.Gomez and S.Mukhanov,
**Probing Quantum Geometry at LHC**,
arXiv:1006.2466 [hep-th], **JHEP 1102 (2011) 012**

[6] M.Kopp, S.Hofmann and J.Weller,
**Separate Universes Do Not Constrain Primordial Black Hole Formation**,
arXiv:1012.4369 [astro-ph.CO], **Phys. Rev. D 83, 124025 (2011)**

[7] F.Berkhahn, D.D.Dietrich and S.Hofmann,
**Self-Protection of Massive Cosmological Gravitons**,
arXiv:1008.0644 [hep-th], **JCAP 1011 (2010) 018**

[1] G.Dvali and C.Gomez,
**Black Hole's Quantum N-Portrait**,
arXiv:1112.3359 [hep-th]

[2] G.Dvali, C.Gomez and S.Mukhanov,
**Black Hole Masses are Quantized**,
arXiv:1106.5894 [hep-ph]

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